diff --git a/.storybook/preview.tsx b/.storybook/preview.tsx
index 757c1f8a7..5b841b829 100644
--- a/.storybook/preview.tsx
+++ b/.storybook/preview.tsx
@@ -7,14 +7,16 @@ Please see LICENSE in the repository root for full details.
 
 import type { Preview } from "@storybook/react-vite";
 import { TooltipProvider } from "@vector-im/compound-web";
-import i18n from "i18next";
 import { logger } from "matrix-js-sdk/lib/logger";
 
 import EN from "../locales/en/app.json";
 import { initReactI18next } from "react-i18next";
+import { i18n } from "../src/utils/i18n";
 import "../src/index.css";
 
-// Bare-minimum i18n config
+// Bare-minimum i18n config.
+// Unlike the app, stories register the instance as react-i18next's default
+// rather than wrapping every story in an <I18nextProvider>.
 i18n
   .use(initReactI18next)
   .init({
diff --git a/README.md b/README.md
index ecbabcf2c..84910ed57 100644
--- a/README.md
+++ b/README.md
@@ -36,8 +36,9 @@ You can find the latest development version continuously deployed to
 ✅ **Decentralized & Federated** – No central authority; works across Matrix
 homeservers.  
 ✅ **End-to-End Encrypted** – Secure and private calls.  
-✅ **Standalone & Widget Mode** – Use as an independent app or embed in Matrix
-clients.  
+✅ **Standalone, Widget & Component Mode** – Use as an independent app, embed
+in Matrix clients as a widget, or (experimentally) mount it as a React component
+inside your own application.  
 ✅ **WebRTC-based** – No additional software required.  
 ✅ **Scalable with LiveKit** – Supports large meetings via SFU
 ([MSC4195: MatrixRTC using LiveKit backend](https://github.com/hughns/matrix-spec-proposals/blob/hughns/matrixrtc-livekit/proposals/4195-matrixrtc-livekit.md)).  
@@ -90,7 +91,9 @@ and voice calls within Matrix rooms.
 
 Element Call offers two packaging options: one for standalone or widget
 deployment, and another for seamless widget-based integration into messenger
-apps. Below is an overview of each option.
+apps. A third, experimental option builds it as a React component library for
+applications that want to render a call inside their own page rather than in an
+iframe. Below is an overview of each option.
 
 **Full Package** – Supports both **Standalone** and **Widget** mode. It is
 hosted as a static web page and can be accessed via a URL when used as a widget.
@@ -107,6 +110,11 @@ recommended method for embedding Element Call.
   <img src="./docs/embedded_package.drawio.png" alt="Element Call Embedded Package">
 </p>
 
+**Component Package (experimental)** – A library build of Element Call as a
+React component, consumed as a dependency by a host application that already
+has a Matrix client. See
+[Element Call as a component](#element-call-as-a-component-experimental) below.
+
 For more details on the packages, see the
 [Embedded vs. Standalone Guide](./docs/embedded_standalone.md).
 
@@ -213,6 +221,94 @@ See also:
 
 - [Developing with linked packages](./docs/linking.md)
 
+#### Element Call as a component (experimental)
+
+Element Call can also be embedded directly into another React application
+rather than being loaded in an iframe as a widget. `pnpm build:component`
+builds it as a library into `component/dist` (the bundle, its stylesheet and
+type declarations), and
+
+```sh
+pnpm dev:component
+```
+
+serves a harness on port 3001 that stands in for such an application: it signs
+in twice against the development backend and shows two calls side by side, in
+resizable boxes, with page furniture of its own around them. Use it to see how
+Element Call behaves when it does not own the page — the size it is given,
+whether it stays inside its container, and what it says to its host, which is
+logged along the bottom. The harness is served with the same development
+certificate as the app, so unless the development CA is trusted, the browser
+needs a certificate exception for `https://localhost:3001` as well (see the
+note under [Backend](#backend)). It reads the same `public/config.json` as
+`pnpm dev` if one exists, and runs with Element Call's defaults otherwise.
+
+The call lays itself out for the size of the element it is mounted in, not the
+window: a host that shrinks the container to a corner of its page gets the
+picture-in-picture layout, just as a host that shrank the whole iframe used to.
+The breakpoints in the stylesheets the component uses are
+`@container element-call` queries against its root element for the same reason;
+for the standalone app the root is the page, so they mean what the media queries
+they replaced did. (The standalone-only views, such as the home and login pages,
+still use plain media queries, since the component never shows them.)
+
+The component's stylesheet is confined to the element it is mounted in: the
+build rewrites every selector so that it matches only Element Call's root or
+what is inside it, with `html`, `body` and `:root` standing for that root (see
+`component/build/scopeStylesToRoot.ts`). A host's own page keeps its styles,
+and Element Call brings its own fonts and design tokens along.
+
+The component speaks every language the app does. English is bundled in; the
+other locales are split into chunks the host's bundler loads the first time
+they are needed. It starts in the browser's language, and follows the host's
+own language setting through the `language` prop (`supportedLanguages` lists
+the tags it accepts, and anything else falls back to its base language or to
+English). The `theme` prop works the same way and takes the same values as the
+widget's `theme` URL parameter: `light`, `dark`, `light-high-contrast` or
+`dark-high-contrast`. Both can change while a call is running without
+disturbing it.
+
+A host must call and await `initializeElementCall(config)` once before
+rendering the component: it loads the `Intl` polyfills, applies the
+deployment-wide `config.json`-style configuration and sets up translations.
+The component itself takes the host's `client` and the `roomId` to call in, an
+`intent` saying what the user asked for (which decides whether to show the
+lobby, ring, and so on), an optional `config` overriding what the intent
+implies, and an optional `hostBridge` through which Element Call tells the host
+that the user has joined or hung up, that it wants to stay on screen, and so
+on. The host makes its own requests (`join`, `hangUp`, `setDeviceMute`) through
+the handle exposed on `ref`. The full API is documented in the type declarations
+(`component/index.tsx` and `component/host.ts`).
+
+A few things differ from the widget on purpose: the component draws a solid
+background rather than a gradient unless told otherwise, never offers to edit
+the user's profile (the account is the host's), scopes its keyboard shortcuts to
+its own root element so that several instances can share a page, and only shows
+its own post-call and error screens when the host has not supplied a `close()`
+callback; with one, it asks the host to unmount it instead. The
+[global JS controls](./docs/controls.md) on `window` are unchanged and remain
+page-wide, so with several instances on one page they apply to all of them.
+
+The package is not published yet. A host installs it as a git dependency on the
+`component` directory of this repository,
+
+```json
+"@element-hq/element-call-component": "github:element-hq/element-call#main&path:/component"
+```
+
+whose `prepare` script runs the build on install. That build needs pnpm (via
+Corepack) on the host's machine, runs a full `pnpm install` of this repository
+and is memory-hungry, since it inherits the `--max-old-space-size` setting of
+the app build; the host's pnpm also has to allow it to run at all
+(`allowBuilds` in its `pnpm-workspace.yaml`). Note that `component/` is a pnpm
+project of its own for this reason, so pnpm commands run from inside that
+directory target it rather than the repository; run them from the repository
+root. The host imports the component from
+`@element-hq/element-call-component` and the stylesheet from
+`@element-hq/element-call-component/style.css`, and has to provide `react`,
+`react-dom`, `matrix-js-sdk` and `livekit-client` itself, since the bundle leaves
+them external.
+
 ### Backend
 
 A docker compose file `docker-compose-dev.yml` is provided to start the
@@ -274,7 +370,10 @@ running Playwright by following
 
 However the Playwright tests are run, an element-call instance must be running
 on https://localhost:3000 (this is configured in `playwright.config.ts`) - this
-is what will be tested.
+is what will be tested. The tests under `playwright/component` instead drive
+the component harness (`pnpm dev:component`) on https://localhost:3001, which
+Playwright starts as a second web server; it is always a Vite dev server, even
+when the app itself is served from Docker with `USE_DOCKER`.
 
 The local backend environment should be running for the test to work:
 `pnpm backend`
@@ -373,7 +472,7 @@ We do this so that we can reuse the labels between repositories.
 
 ## 📝 Copyright & License
 
-Copyright 2021-2025 New Vector Ltd
+Copyright 2021-2026 New Vector Ltd
 
 This software is dual-licensed by New Vector Ltd (Element). It can be used
 either:
diff --git a/component/ElementCall.module.css b/component/ElementCall.module.css
new file mode 100644
index 000000000..91213e422
--- /dev/null
+++ b/component/ElementCall.module.css
@@ -0,0 +1,43 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/* The container a host mounts us into. It fills whatever space the host gives
+it, and nothing we draw may leave it.
+
+That takes two separate things, which are easy to mistake for one. `isolation`
+gives us a stacking context, so nothing inside can be layered above the host's
+own interface. Containment makes us the containing block for `position: fixed`
+descendants, and clips what we paint to our own box: without it, the modal
+scrim and dialog — which are positioned `fixed` and centred, since in the app
+they are meant to cover the page — resolve against the viewport and appear in
+the middle of the host's window rather than in the middle of the call.
+
+The clipping cuts both ways: a menu near the edge of a small container is
+trimmed rather than overflowing into the host. That is the trade being a
+component rather than a page makes. */
+.root {
+  display: flex;
+  flex-direction: column;
+  inline-size: 100%;
+  block-size: 100%;
+  isolation: isolate;
+  contain: layout paint;
+  position: relative;
+  background-color: var(--cpd-color-bg-canvas-default);
+  color: var(--cpd-color-text-primary);
+  -webkit-font-smoothing: antialiased;
+  -moz-osx-font-smoothing: grayscale;
+  -webkit-tap-highlight-color: transparent;
+}
+
+/* Compound's overlay container, which holds tooltips and popovers, has to fill
+the container for the elements inside it to be positioned against it. The
+standalone page does the same for the container under `#root`. */
+.root > [data-overlay-container] {
+  position: relative;
+  block-size: 100%;
+}
diff --git a/component/build/scopeStylesToRoot.test.ts b/component/build/scopeStylesToRoot.test.ts
new file mode 100644
index 000000000..ae42062c3
--- /dev/null
+++ b/component/build/scopeStylesToRoot.test.ts
@@ -0,0 +1,112 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, it } from "vitest";
+import postcss from "postcss";
+
+import { ROOT_SELECTOR, scopeStylesToRoot } from "./scopeStylesToRoot";
+
+const inRoot = `:where(${ROOT_SELECTOR}, ${ROOT_SELECTOR} *)`;
+const isRoot = `:where(${ROOT_SELECTOR})`;
+
+async function scope(css: string, file = "base.css"): Promise<string> {
+  const result = await postcss([scopeStylesToRoot()]).process(css, {
+    from: file,
+  });
+  return result.css;
+}
+
+describe("scopeStylesToRoot", () => {
+  it("makes the root stand in for the document", async () => {
+    expect(await scope("html { line-height: 1.15 }")).toBe(
+      `${isRoot} { line-height: 1.15 }`,
+    );
+    expect(await scope("body { margin: 0 }")).toBe(`${isRoot} { margin: 0 }`);
+    expect(await scope(":root { --a: 1 }")).toBe(`${isRoot} { --a: 1 }`);
+    expect(await scope("body.no-scroll-body { position: fixed }")).toBe(
+      `${isRoot}.no-scroll-body { position: fixed }`,
+    );
+    expect(await scope("body .x { color: red }")).toBe(
+      `${isRoot} .x { color: red }`,
+    );
+  });
+
+  it("collapses selectors that all became the root", async () => {
+    expect(await scope("html, body, input { font: inherit }")).toBe(
+      `${isRoot},input${inRoot} { font: inherit }`,
+    );
+  });
+
+  it("confines everything else to the root and what is inside it", async () => {
+    expect(await scope("h1 { margin: 0 }")).toBe(`h1${inRoot} { margin: 0 }`);
+    expect(await scope(".cpd-theme-dark { --a: 1 }")).toBe(
+      `.cpd-theme-dark${inRoot} { --a: 1 }`,
+    );
+    expect(await scope("* { box-sizing: border-box }")).toBe(
+      `*${inRoot} { box-sizing: border-box }`,
+    );
+    expect(await scope(".a > .b + .c { color: red }")).toBe(
+      `.a>.b+.c${inRoot} { color: red }`,
+    );
+  });
+
+  it("keeps pseudo-elements last", async () => {
+    expect(await scope("button::-moz-focus-inner { border: 0 }")).toBe(
+      `button${inRoot}::-moz-focus-inner { border: 0 }`,
+    );
+    expect(await scope(".a .b:hover::after { content: '' }")).toBe(
+      `.a .b:hover${inRoot}::after { content: '' }`,
+    );
+    expect(await scope("p:first-letter { color: red }")).toBe(
+      `p${inRoot}:first-letter { color: red }`,
+    );
+  });
+
+  it("leaves alone what already names the root", async () => {
+    const css = `${ROOT_SELECTOR}[data-platform="ios"] { --a: 1 }`;
+    expect(await scope(css)).toBe(css);
+  });
+
+  it("reaches into layers and media queries", async () => {
+    expect(
+      await scope(
+        "@layer normalize { h1 { margin: 0 } } @media (min-width: 1px) { p { margin: 0 } }",
+      ),
+    ).toBe(
+      `@layer normalize { h1${inRoot} { margin: 0 } } @media (min-width: 1px) { p${inRoot} { margin: 0 } }`,
+    );
+  });
+
+  it("does not touch keyframes or nested rules", async () => {
+    expect(
+      await scope("@keyframes spin { from { opacity: 0 } to { opacity: 1 } }"),
+    ).toBe("@keyframes spin { from { opacity: 0 } to { opacity: 1 } }");
+    expect(
+      await scope(
+        ".a { color: red; &:hover { color: blue } .b { color: green } }",
+      ),
+    ).toBe(
+      `.a${inRoot} { color: red; &:hover { color: blue } .b { color: green } }`,
+    );
+  });
+
+  it("only touches the bare selectors of a CSS module", async () => {
+    const file = "Settings.module.css";
+    expect(await scope("pre { font-size: 1px }", file)).toBe(
+      `pre${inRoot} { font-size: 1px }`,
+    );
+    expect(await scope(".modal pre { font-size: 1px }", file)).toBe(
+      `.modal pre${inRoot} { font-size: 1px }`,
+    );
+    expect(await scope(".box_abc12 { border: 0 }", file)).toBe(
+      ".box_abc12 { border: 0 }",
+    );
+    expect(await scope(".a .b_abc12:hover { border: 0 }", file)).toBe(
+      ".a .b_abc12:hover { border: 0 }",
+    );
+  });
+});
diff --git a/component/build/scopeStylesToRoot.ts b/component/build/scopeStylesToRoot.ts
new file mode 100644
index 000000000..9e7e80376
--- /dev/null
+++ b/component/build/scopeStylesToRoot.ts
@@ -0,0 +1,161 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  type AtRule,
+  type Container,
+  type Document,
+  type Plugin,
+  type Rule,
+} from "postcss";
+import selectorParser, {
+  type Node,
+  type Pseudo,
+  type Selector,
+} from "postcss-selector-parser";
+
+/**
+ * How the stylesheets find Element Call's root element. The attribute is put
+ * there by `useTheme`, on the container the host gives the component.
+ */
+export const ROOT_SELECTOR = "[data-element-call-root]";
+
+// Both are `:where()`, which has no specificity of its own, so the rules keep
+// exactly the weight they had before being scoped and nothing in Element Call's
+// cascade changes — only where it applies.
+//
+// The root, or anything inside it. Appended to the element a rule is about,
+// rather than prepended to the whole selector, so that a rule about the root
+// itself (its theme class, say) still matches.
+const IN_ROOT = `:where(${ROOT_SELECTOR}, ${ROOT_SELECTOR} *)`;
+// The root itself, standing in for the document.
+const IS_ROOT = `:where(${ROOT_SELECTOR})`;
+
+/**
+ * Confines a stylesheet to Element Call's root element, for the build of
+ * Element Call as a component.
+ *
+ * As a page of its own, Element Call can style the document: normalize.css and
+ * Compound speak of `html`, `body` and bare elements, and the design tokens are
+ * declared on `:root`. As a component, all of that would land on the host's
+ * document too. This rewrites every selector so that it matches only the root
+ * or its descendants:
+ *
+ * - `html`, `body` and `:root` become the root element, which is what stands in
+ *   for the document inside a host.
+ * - Everything else keeps its selector and gains `:where([data-element-call-root],
+ *   [data-element-call-root] *)` on the element it styles.
+ * - Selectors that already name the root are left alone, as are keyframe
+ *   selectors and rules nested inside another rule, which are relative to it.
+ *
+ * CSS modules are scoped by their class names already, so only their selectors
+ * that would match by element alone — `pre` rather than `.pre` — are touched.
+ *
+ * The root's fonts and design tokens are still inherited by everything inside
+ * it, the way they were from `body` and `:root`, and `@font-face` declarations
+ * stay global, which they are by nature.
+ */
+export function scopeStylesToRoot(): Plugin {
+  return {
+    postcssPlugin: "element-call-scope-styles-to-root",
+    Once(root) {
+      const isModule =
+        root.source?.input.file?.endsWith(".module.css") ?? false;
+      root.walkRules((rule) => {
+        if (isRelative(rule)) return;
+        rule.selector = (isModule ? scopeBare : scopeAll).processSync(
+          rule.selector,
+          { lossless: false },
+        );
+      });
+    },
+  };
+}
+
+/** Whether a rule's selectors are relative to something other than the document. */
+function isRelative(rule: Rule): boolean {
+  let parent: Container | Document | undefined = rule.parent;
+  while (parent !== undefined) {
+    if (parent.type === "rule") return true;
+    if (parent.type === "atrule") {
+      const { name } = parent as AtRule;
+      if (name.endsWith("keyframes") || name === "page") return true;
+    }
+    parent = parent.parent;
+  }
+  return false;
+}
+
+const processor = (isModule: boolean): ReturnType<typeof selectorParser> =>
+  selectorParser((selectors) => {
+    selectors.each((selector) => {
+      scopeSelector(selector, isModule);
+    });
+    // Mapping `html, body` onto the root leaves the same selector twice
+    const seen = new Set<string>();
+    selectors.each((selector) => {
+      const text = String(selector).trim();
+      if (seen.has(text)) selector.remove();
+      else seen.add(text);
+    });
+  });
+
+// Everything, for stylesheets that speak of the document; only what a class
+// does not already confine, for CSS modules
+const scopeAll = processor(false);
+const scopeBare = processor(true);
+
+function scopeSelector(selector: Selector, isModule: boolean): void {
+  if (String(selector).includes(ROOT_SELECTOR)) return;
+
+  const compounds = splitCompounds(selector);
+  if (compounds.length === 0) return;
+
+  // Something said of the document is said of the root instead
+  const document = compounds[0].find(isDocumentSelector);
+  if (document !== undefined) {
+    document.replaceWith(pseudo(IS_ROOT));
+    return;
+  }
+
+  const subject = compounds.at(-1)!;
+  if (isModule && subject.some((node) => node.type === "class")) return;
+
+  // Pseudo-elements have to come last in a compound selector
+  const pseudoElement = subject.find(isPseudoElement);
+  if (pseudoElement === undefined) selector.append(pseudo(IN_ROOT));
+  else selector.insertBefore(pseudoElement, pseudo(IN_ROOT));
+}
+
+/** The compound selectors making up a complex selector, in order. */
+function splitCompounds(selector: Selector): Node[][] {
+  const compounds: Node[][] = [[]];
+  for (const node of selector.nodes) {
+    if (node.type === "combinator") compounds.push([]);
+    else if (node.type !== "comment") compounds.at(-1)!.push(node);
+  }
+  return compounds.filter((compound) => compound.length > 0);
+}
+
+function isDocumentSelector(node: Node): boolean {
+  return (
+    (node.type === "tag" && (node.value === "html" || node.value === "body")) ||
+    (node.type === "pseudo" && node.value === ":root")
+  );
+}
+
+function isPseudoElement(node: Node): node is Pseudo {
+  if (node.type !== "pseudo") return false;
+  return (
+    node.value.startsWith("::") ||
+    [":before", ":after", ":first-line", ":first-letter"].includes(node.value)
+  );
+}
+
+function pseudo(text: string): Pseudo {
+  return selectorParser().astSync(text).nodes[0].nodes[0].clone() as Pseudo;
+}
diff --git a/component/dev/DevHostBridge.ts b/component/dev/DevHostBridge.ts
new file mode 100644
index 000000000..b69779a94
--- /dev/null
+++ b/component/dev/DevHostBridge.ts
@@ -0,0 +1,46 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type ElementCallHostBridge } from "../index";
+
+/**
+ * A host bridge that reports everything it is told, so that the harness can
+ * watch what Element Call says to its host. (What the host says to Element
+ * Call goes through the component's handle, and is logged by the pane.)
+ */
+export function createDevHostBridge(
+  log: (message: string) => void,
+  /** What the host does when Element Call asks to be closed. */
+  onClose: () => void,
+): ElementCallHostBridge {
+  /**
+   * Records something Element Call told the host. Nothing is sent anywhere, so
+   * this is only asynchronous because a real host's answer would have to be.
+   */
+  const told = async (message: string): Promise<void> => {
+    log(`→ ${message}`);
+    await Promise.resolve();
+  };
+
+  return {
+    setAlwaysOnScreen: async (alwaysOnScreen): Promise<void> =>
+      await told(`setAlwaysOnScreen(${alwaysOnScreen})`),
+    contentLoaded: async (): Promise<void> => await told("contentLoaded"),
+    notifyJoined: async (): Promise<void> => await told("notifyJoined"),
+    notifyHungUp: async (): Promise<void> => await told("notifyHungUp"),
+    notifyDeviceMute: async (state): Promise<void> =>
+      await told(
+        `notifyDeviceMute(audio: ${state.audio_enabled}, video: ${state.video_enabled})`,
+      ),
+    // Present because this host really can dismiss Element Call, which is what
+    // makes it offer a close affordance at all
+    close: async (): Promise<void> => {
+      await told("close");
+      onClose();
+    },
+  };
+}
diff --git a/component/dev/Harness.module.css b/component/dev/Harness.module.css
new file mode 100644
index 000000000..0b116a242
--- /dev/null
+++ b/component/dev/Harness.module.css
@@ -0,0 +1,140 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+.credentials {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  max-inline-size: 420px;
+  margin: 48px auto;
+  padding: 24px;
+  background-color: #ffffff;
+  border: 1px solid #d4d4d8;
+  border-radius: 8px;
+}
+
+.field {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+}
+
+.error {
+  color: #b91c1c;
+}
+
+.harness {
+  display: grid;
+  grid-template-rows: auto 1fr auto;
+  block-size: 100%;
+}
+
+.header,
+.paneBar {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  padding: 8px 12px;
+  border-block-end: 1px solid #d4d4d8;
+  background-color: #ffffff;
+}
+
+.header h1 {
+  font-size: 16px;
+  margin: 0;
+}
+
+.middle {
+  display: flex;
+  min-block-size: 0;
+}
+
+.sidebar {
+  flex: 0 0 220px;
+  padding: 12px;
+  border-inline-end: 1px solid #d4d4d8;
+  background-color: #ffffff;
+  overflow-y: auto;
+}
+
+.panes {
+  display: flex;
+  flex-wrap: wrap;
+  /* So that a pane is the size it was dragged to, rather than being stretched
+  to fill the row */
+  align-items: flex-start;
+  align-content: flex-start;
+  gap: 16px;
+  padding: 16px;
+  flex: 1;
+  min-inline-size: 0;
+  overflow: auto;
+}
+
+.pane {
+  display: flex;
+  flex-direction: column;
+  border: 1px solid #d4d4d8;
+  border-radius: 8px;
+  overflow: hidden;
+  background-color: #ffffff;
+}
+
+.paneBar {
+  flex-wrap: wrap;
+  gap: 6px;
+  border-block-end: none;
+}
+
+/* The space the host gives Element Call. Resizable so that the sizes it has to
+cope with can be found by dragging rather than by rebuilding, and `overflow:
+hidden` both to enable the resize handle and to show up anything inside Element
+Call that does not fit the box it was given. */
+.paneCall {
+  inline-size: 560px;
+  block-size: 420px;
+  min-inline-size: 180px;
+  min-block-size: 180px;
+  resize: both;
+  overflow: hidden;
+}
+
+.log {
+  max-block-size: 180px;
+  overflow-y: auto;
+  padding: 8px 12px;
+  border-block-start: 1px solid #d4d4d8;
+  background-color: #ffffff;
+  font-size: 12px;
+}
+
+.log h2 {
+  font-size: 13px;
+  margin: 0 0 4px;
+}
+
+.log ol {
+  margin: 0;
+  padding: 0;
+  list-style: none;
+}
+
+/* A host overlay, which Element Call must not be able to draw over */
+.dialogScrim {
+  position: fixed;
+  inset: 0;
+  display: grid;
+  place-items: center;
+  background-color: rgb(0 0 0 / 50%);
+  z-index: 10;
+}
+
+.dialog {
+  padding: 24px;
+  border-radius: 8px;
+  background-color: #ffffff;
+}
diff --git a/component/dev/Harness.tsx b/component/dev/Harness.tsx
new file mode 100644
index 000000000..ded9155a9
--- /dev/null
+++ b/component/dev/Harness.tsx
@@ -0,0 +1,380 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  type FC,
+  type FormEvent,
+  type ReactNode,
+  useCallback,
+  useMemo,
+  useRef,
+  useState,
+} from "react";
+import { type MatrixClient } from "matrix-js-sdk";
+import { logger } from "matrix-js-sdk/lib/logger";
+
+import {
+  ElementCall,
+  type ElementCallHandle,
+  supportedLanguages,
+} from "../index";
+import { createDevHostBridge } from "./DevHostBridge";
+import { createSession, joinRoom } from "./session";
+import styles from "./Harness.module.css";
+
+interface Credentials {
+  homeserver: string;
+  username: string;
+  password: string;
+  room: string;
+}
+
+const CREDENTIALS_KEY = "element-call-component-harness";
+
+const DEFAULT_CREDENTIALS: Credentials = {
+  homeserver: "https://synapse.m.localhost",
+  username: "",
+  password: "",
+  room: "",
+};
+
+/**
+ * The credentials to start with: the last ones used, so that a reload does not
+ * mean typing them again, overridden by anything in the query string.
+ *
+ * A host reading its own URL is entirely proper — it was Element Call doing so
+ * that was the mistake. It lets the end-to-end tests, or a shared link, say
+ * which account and room to use.
+ */
+function loadCredentials(): Credentials {
+  let stored: Partial<Credentials> = {};
+  try {
+    const json = localStorage.getItem(CREDENTIALS_KEY);
+    if (json !== null) stored = JSON.parse(json) as Credentials;
+  } catch (e) {
+    logger.warn("Could not read the stored harness credentials", e);
+  }
+
+  const query = new URLSearchParams(location.search);
+  const fromUrl = Object.fromEntries(
+    (["homeserver", "username", "password", "room"] as const)
+      .map((name) => [name, query.get(name)])
+      .filter(([, value]) => value !== null),
+  ) as Partial<Credentials>;
+
+  return { ...DEFAULT_CREDENTIALS, ...stored, ...fromUrl };
+}
+
+interface Session {
+  label: string;
+  client: MatrixClient;
+}
+
+type State =
+  | { phase: "credentials" }
+  | { phase: "starting"; progress: string }
+  | { phase: "started"; roomId: string; sessions: Session[] }
+  | { phase: "failed"; error: string };
+
+interface LogEntry {
+  pane: string;
+  message: string;
+  at: string;
+}
+
+/**
+ * One Element Call component, with the controls a host would have over it: the
+ * requests it can make of Element Call, and the ability to take it off screen
+ * altogether.
+ */
+const Pane: FC<{
+  session: Session;
+  roomId: string;
+  theme: string | undefined;
+  language: string | undefined;
+  log: (pane: string, message: string) => void;
+}> = ({ session, roomId, theme, language, log }): ReactNode => {
+  const [mounted, setMounted] = useState(true);
+
+  const bridge = useMemo(
+    () =>
+      createDevHostBridge(
+        (message) => log(session.label, message),
+        () => setMounted(false),
+      ),
+    [log, session.label],
+  );
+
+  // What the host asks of Element Call goes through the component's handle.
+  // Worth saying out loud when a request is refused — asking to hang up when
+  // there is no call, say — since that is the sort of thing the harness is for.
+  const handle = useRef<ElementCallHandle>(null);
+  const ask = (
+    name: string,
+    make: (handle: ElementCallHandle) => Promise<unknown>,
+  ): void => {
+    if (handle.current === null) {
+      log(session.label, `← ${name}: not mounted`);
+      return;
+    }
+    log(session.label, `← ${name}`);
+    make(handle.current).then(
+      (reply) =>
+        log(
+          session.label,
+          `→ ${name} acknowledged${reply === undefined ? "" : `: ${JSON.stringify(reply)}`}`,
+        ),
+      (e: unknown) => log(session.label, `→ ${name} refused: ${e}`),
+    );
+  };
+
+  return (
+    <section className={styles.pane} data-testid="call-pane">
+      <div className={styles.paneBar}>
+        <strong>{session.label}</strong>
+        <code>{session.client.getDeviceId()}</code>
+        <button onClick={(): void => setMounted((m) => !m)}>
+          {mounted ? "Unmount" : "Mount"}
+        </button>
+        <button
+          onClick={(): void =>
+            ask(
+              "setDeviceMute(audio: false)",
+              async (h) => await h.setDeviceMute({ audio_enabled: false }),
+            )
+          }
+        >
+          Mute
+        </button>
+        <button
+          onClick={(): void => ask("hangUp", async (h) => await h.hangUp())}
+        >
+          Hang up
+        </button>
+      </div>
+      {/* Resizable, because how Element Call copes with the size it is given is
+      one of the things we cannot find out from the standalone app */}
+      <div className={styles.paneCall} data-testid="call-container">
+        {mounted && (
+          <ElementCall
+            ref={handle}
+            client={session.client}
+            roomId={roomId}
+            hostBridge={bridge}
+            theme={theme}
+            language={language}
+          />
+        )}
+      </div>
+    </section>
+  );
+};
+
+/** Host furniture, to make it visible if Element Call styles anything but itself. */
+const HostChrome: FC = (): ReactNode => (
+  <nav className={styles.sidebar}>
+    <h2>Host chrome</h2>
+    <p>
+      This column belongs to the host. If Element Call&apos;s stylesheet reaches
+      outside its own container, it shows up here.
+    </p>
+    <hr />
+    <ul>
+      <li>Some room</li>
+      <li>Another room</li>
+    </ul>
+    <button>A host button</button>
+  </nav>
+);
+
+/**
+ * A dialog of the host's own, over the top of the calls. Element Call as a
+ * component has to sit underneath this — being unable to is one of the reasons
+ * for a component rather than an iframe.
+ */
+const HostDialog: FC<{ onClose: () => void }> = ({ onClose }): ReactNode => (
+  <div className={styles.dialogScrim}>
+    <div className={styles.dialog}>
+      <h2>A dialog belonging to the host</h2>
+      <p>This should cover the calls completely.</p>
+      <button onClick={onClose}>Close</button>
+    </div>
+  </div>
+);
+
+/**
+ * Stands in for a host application using the Element Call component: it owns the Matrix
+ * clients, the page and the space each call is given, and reaches Element Call
+ * only through the component's public interface.
+ *
+ * Two calls at once, from two devices of the same account, so that a real call
+ * happens between them and anything Element Call keeps once per process rather
+ * than once per call shows itself.
+ */
+export const Harness: FC = (): ReactNode => {
+  const [credentials, setCredentials] = useState(loadCredentials);
+  const [state, setState] = useState<State>({ phase: "credentials" });
+  const [entries, setEntries] = useState<LogEntry[]>([]);
+  const [dialogOpen, setDialogOpen] = useState(false);
+  // The host's language setting, which Element Call follows. Undefined means
+  // the host has none and Element Call uses the browser's.
+  const [language, setLanguage] = useState<string | undefined>(undefined);
+  const [theme, setTheme] = useState<string | undefined>(undefined);
+
+  const log = useCallback((pane: string, message: string): void => {
+    setEntries((entries) =>
+      [
+        ...entries,
+        { pane, message, at: new Date().toLocaleTimeString() },
+      ].slice(-100),
+    );
+  }, []);
+
+  const start = useCallback(
+    (event: FormEvent): void => {
+      event.preventDefault();
+      localStorage.setItem(CREDENTIALS_KEY, JSON.stringify(credentials));
+      const { homeserver, username, password, room } = credentials;
+
+      const progress = (message: string): void =>
+        setState({ phase: "starting", progress: message });
+      progress("Starting");
+
+      void (async (): Promise<void> => {
+        try {
+          // One at a time: two logins at once from the same account is the
+          // shape of request homeservers rate limit
+          const sessions: Session[] = [];
+          for (const label of ["Call A", "Call B"])
+            sessions.push({
+              label,
+              client: await createSession(
+                homeserver,
+                username,
+                password,
+                (message) => progress(`${label}: ${message}`),
+              ),
+            });
+
+          progress("Joining the room");
+          let roomId = room;
+          for (const { client } of sessions)
+            roomId = await joinRoom(client, roomId);
+
+          setState({ phase: "started", roomId, sessions });
+        } catch (e) {
+          logger.error("The harness could not start", e);
+          setState({ phase: "failed", error: `${e}` });
+        }
+      })();
+    },
+    [credentials],
+  );
+
+  const field = (
+    name: keyof Credentials,
+    label: string,
+    type = "text",
+  ): ReactNode => (
+    <label className={styles.field}>
+      {label}
+      <input
+        type={type}
+        value={credentials[name]}
+        onChange={(e): void =>
+          setCredentials((c) => ({ ...c, [name]: e.target.value }))
+        }
+      />
+    </label>
+  );
+
+  if (state.phase !== "started")
+    return (
+      <form className={styles.credentials} onSubmit={start}>
+        <h1>Element Call component harness</h1>
+        <p>
+          Signs in twice and shows the Element Call component twice, in a page
+          that is not Element Call&apos;s own.
+        </p>
+        {field("homeserver", "Homeserver")}
+        {field("username", "Username")}
+        {field("password", "Password", "password")}
+        {field("room", "Room ID or alias")}
+        <button type="submit" disabled={state.phase === "starting"}>
+          Start
+        </button>
+        {state.phase === "starting" && <p>{state.progress}</p>}
+        {state.phase === "failed" && (
+          <p className={styles.error}>{state.error}</p>
+        )}
+      </form>
+    );
+
+  return (
+    <div className={styles.harness}>
+      <header className={styles.header}>
+        <h1>Element Call component harness</h1>
+        <code>{state.roomId}</code>
+        <button onClick={(): void => setDialogOpen(true)}>
+          Open a host dialog
+        </button>
+        <label>
+          Theme{" "}
+          <select
+            value={theme ?? ""}
+            onChange={(e): void => setTheme(e.target.value || undefined)}
+          >
+            <option value="">Element Call&apos;s choice</option>
+            <option value="light">light</option>
+            <option value="dark">dark</option>
+          </select>
+        </label>
+        <label>
+          Language{" "}
+          <select
+            value={language ?? ""}
+            onChange={(e): void => setLanguage(e.target.value || undefined)}
+          >
+            <option value="">Browser default</option>
+            {supportedLanguages.map((tag) => (
+              <option key={tag} value={tag}>
+                {tag}
+              </option>
+            ))}
+          </select>
+        </label>
+      </header>
+      <div className={styles.middle}>
+        <HostChrome />
+        <main className={styles.panes}>
+          {state.sessions.map((session) => (
+            <Pane
+              key={session.label}
+              session={session}
+              roomId={state.roomId}
+              theme={theme}
+              language={language}
+              log={log}
+            />
+          ))}
+        </main>
+      </div>
+      <section className={styles.log} data-testid="bridge-log">
+        <h2>Host bridge</h2>
+        <ol>
+          {entries.map((entry, i) => (
+            <li key={i}>
+              <code>{entry.at}</code> <strong>{entry.pane}</strong>{" "}
+              {entry.message}
+            </li>
+          ))}
+        </ol>
+      </section>
+      {dialogOpen && <HostDialog onClose={(): void => setDialogOpen(false)} />}
+    </div>
+  );
+};
diff --git a/component/dev/host.css b/component/dev/host.css
new file mode 100644
index 000000000..76e70f609
--- /dev/null
+++ b/component/dev/host.css
@@ -0,0 +1,23 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/* The host page's own styles. Deliberately plain, and deliberately not using
+Element Call's design tokens: the harness should look like it does because of
+this file, not because Element Call styled it. */
+
+html,
+body,
+#root {
+  height: 100%;
+}
+
+body {
+  margin: 0;
+  font-family: system-ui, sans-serif;
+  background-color: #f4f4f5;
+  color: #18181b;
+}
diff --git a/component/dev/index.html b/component/dev/index.html
new file mode 100644
index 000000000..7174e935a
--- /dev/null
+++ b/component/dev/index.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<!--
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+-->
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Element Call component harness</title>
+  </head>
+  <body>
+    <!-- Deliberately plain: this page stands in for a host application, so
+    anything it looks like must have come from the host's own styles or from
+    Element Call reaching outside its container. -->
+    <div id="root"></div>
+    <script type="module" src="./main.tsx"></script>
+  </body>
+</html>
diff --git a/component/dev/main.tsx b/component/dev/main.tsx
new file mode 100644
index 000000000..9150678d5
--- /dev/null
+++ b/component/dev/main.tsx
@@ -0,0 +1,42 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import { logger } from "matrix-js-sdk/lib/logger";
+
+import { type ConfigOptions, initializeElementCall } from "../index";
+import { Harness } from "./Harness";
+// After Element Call's, so that the host has the last word on its own page
+import "./host.css";
+
+/**
+ * The development app's own `config.json`, so that the harness runs Element
+ * Call the way `pnpm dev` does. It is not in the repository — developers copy
+ * it from `config/config.devenv.json` — so its absence is expected rather than
+ * an error.
+ */
+async function loadConfig(): Promise<ConfigOptions> {
+  try {
+    const response = await fetch("/config.json");
+    if (response.ok) return (await response.json()) as ConfigOptions;
+    logger.warn(
+      `No config.json (${response.status}); running with Element Call's defaults`,
+    );
+  } catch (e) {
+    logger.warn("Could not read config.json", e);
+  }
+  return {};
+}
+
+await initializeElementCall(await loadConfig());
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <Harness />
+  </StrictMode>,
+);
diff --git a/component/dev/session.ts b/component/dev/session.ts
new file mode 100644
index 000000000..5a424a409
--- /dev/null
+++ b/component/dev/session.ts
@@ -0,0 +1,79 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import {
+  ClientEvent,
+  createClient,
+  type MatrixClient,
+  MemoryStore,
+  SyncState,
+} from "matrix-js-sdk";
+
+/**
+ * Logs in and brings up a client the way a host application would, so that the
+ * component is handed a real one rather than something Element Call built for
+ * itself.
+ *
+ * Everything is kept in memory and a fresh login happens on every reload. That
+ * costs a device on the development homeserver each time, which is harmless,
+ * and buys the harness two clients that cannot tread on each other's storage.
+ * Persisting the login to make reloads quicker would mean persisting the
+ * crypto store too: reusing a device ID with a fresh crypto store generates new
+ * device keys, and uploading them conflicts with the ones the server already
+ * holds.
+ */
+export async function createSession(
+  homeserver: string,
+  username: string,
+  password: string,
+  onProgress: (message: string) => void,
+): Promise<MatrixClient> {
+  onProgress("Logging in");
+  const login = await createClient({ baseUrl: homeserver }).login(
+    "m.login.password",
+    { identifier: { type: "m.id.user", user: username }, password },
+  );
+
+  const client = createClient({
+    baseUrl: homeserver,
+    accessToken: login.access_token,
+    userId: login.user_id,
+    deviceId: login.device_id,
+    store: new MemoryStore(),
+    useAuthorizationHeader: true,
+    fallbackICEServerAllowed: true,
+  });
+
+  onProgress(`Setting up crypto for ${login.device_id}`);
+  await client.initRustCrypto({ useIndexedDB: false });
+
+  onProgress(`Syncing ${login.device_id}`);
+  await client.startClient();
+  await new Promise<void>((resolve) => {
+    const onSync = (state: SyncState): void => {
+      if (state !== SyncState.Prepared && state !== SyncState.Syncing) return;
+      client.off(ClientEvent.Sync, onSync);
+      resolve();
+    };
+    client.on(ClientEvent.Sync, onSync);
+  });
+
+  return client;
+}
+
+/**
+ * The room to call in, joining it if this session is not in it yet — a host
+ * hands Element Call a room it already knows about, so the harness has to get
+ * itself into that position first.
+ */
+export async function joinRoom(
+  client: MatrixClient,
+  roomIdOrAlias: string,
+): Promise<string> {
+  const room = await client.joinRoom(roomIdOrAlias);
+  return room.roomId;
+}
diff --git a/component/host.test.ts b/component/host.test.ts
new file mode 100644
index 000000000..696470cd9
--- /dev/null
+++ b/component/host.test.ts
@@ -0,0 +1,161 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { renderHook } from "@testing-library/react";
+import { createRef } from "react";
+import { describe, expect, test, vi } from "vitest";
+
+import {
+  type ElementCallHandle,
+  type ElementCallHostBridge,
+  useComponentHostBridge,
+} from "./host";
+
+describe("useComponentHostBridge", () => {
+  test("keeps one identity while the host supplies new objects", () => {
+    const { result, rerender } = renderHook(
+      ({ supplied }: { supplied: ElementCallHostBridge }) =>
+        useComponentHostBridge(supplied, undefined, undefined),
+      { initialProps: { supplied: {} } },
+    );
+    const first = result.current;
+    rerender({ supplied: { notifyJoined: async () => {} } });
+    expect(result.current).toBe(first);
+  });
+
+  test("forwards to whatever the host most recently supplied", async () => {
+    const before = vi.fn().mockResolvedValue(undefined);
+    const after = vi.fn().mockResolvedValue(undefined);
+    const { result, rerender } = renderHook(
+      ({ supplied }: { supplied: ElementCallHostBridge }) =>
+        useComponentHostBridge(supplied, undefined, undefined),
+      { initialProps: { supplied: { notifyJoined: before } } },
+    );
+    rerender({ supplied: { notifyJoined: after } });
+
+    await result.current.notifyJoined();
+    expect(before).not.toHaveBeenCalled();
+    expect(after).toHaveBeenCalledOnce();
+  });
+
+  test("is quiet about what the host did not implement", async () => {
+    const { result } = renderHook(() =>
+      useComponentHostBridge(undefined, undefined, undefined),
+    );
+    await expect(result.current.contentLoaded()).resolves.toBeUndefined();
+    await expect(
+      result.current.notifyDeviceMute({
+        audio_enabled: true,
+        video_enabled: false,
+      }),
+    ).resolves.toBeUndefined();
+    expect(result.current.supportsReactions).toBe(true);
+    // Starting the user unmuted unasked is something a host has to opt into
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(false);
+  });
+
+  test("lets the host allow joining unmuted on the intent", () => {
+    const { result, rerender } = renderHook(
+      ({ supplied }: { supplied: ElementCallHostBridge }) =>
+        useComponentHostBridge(supplied, undefined, undefined),
+      { initialProps: { supplied: {} } },
+    );
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(false);
+
+    // Read through to whatever the host most recently said
+    rerender({ supplied: { allowJoinUnmutedViaIntent: true } });
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(true);
+  });
+
+  test("only has a close when the host has one, since that is a signal", () => {
+    const { result, rerender } = renderHook(
+      ({ supplied }: { supplied: ElementCallHostBridge }) =>
+        useComponentHostBridge(supplied, undefined, undefined),
+      { initialProps: { supplied: {} } },
+    );
+    expect(result.current.close).toBeUndefined();
+
+    const close = vi.fn().mockResolvedValue(undefined);
+    rerender({ supplied: { close } });
+    expect(result.current.close).toBeDefined();
+  });
+
+  test("never offers profile changes, since the account is the host's", () => {
+    const { result } = renderHook(() =>
+      useComponentHostBridge(undefined, undefined, undefined),
+    );
+    expect(result.current.supportsProfileChanges).toBe(false);
+  });
+
+  describe("the handle", () => {
+    test("delivers a request to what is listening and resolves on its reply", async () => {
+      const ref = createRef<ElementCallHandle>();
+      const { result } = renderHook(() =>
+        useComponentHostBridge(undefined, ref, undefined),
+      );
+
+      const received = vi.fn();
+      result.current.deviceMute$.subscribe(({ data, reply }) => {
+        received(data);
+        reply({ audio_enabled: data.audio_enabled!, video_enabled: true });
+      });
+
+      await expect(
+        ref.current!.setDeviceMute({ audio_enabled: false }),
+      ).resolves.toEqual({ audio_enabled: false, video_enabled: true });
+      expect(received).toHaveBeenCalledWith({ audio_enabled: false });
+    });
+
+    test("refuses a request nothing in Element Call is listening for", async () => {
+      const ref = createRef<ElementCallHandle>();
+      renderHook(() => useComponentHostBridge(undefined, ref, undefined));
+
+      await expect(ref.current!.hangUp()).rejects.toThrow(
+        "Nothing in Element Call can hang up right now",
+      );
+    });
+  });
+
+  describe("the theme", () => {
+    test("reaches a subscriber that arrives after it was set", () => {
+      const { result } = renderHook(() =>
+        useComponentHostBridge(undefined, undefined, "light"),
+      );
+      const names: (string | undefined)[] = [];
+      result.current.themeChange$.subscribe(({ data }) =>
+        names.push(data.name),
+      );
+      expect(names).toEqual(["light"]);
+    });
+
+    test("follows the prop", () => {
+      const { result, rerender } = renderHook(
+        ({ theme }: { theme: string | undefined }) =>
+          useComponentHostBridge(undefined, undefined, theme),
+        { initialProps: { theme: "light" } },
+      );
+      const names: (string | undefined)[] = [];
+      result.current.themeChange$.subscribe(({ data }) =>
+        names.push(data.name),
+      );
+
+      rerender({ theme: "dark" });
+      expect(names).toEqual(["light", "dark"]);
+    });
+
+    test("says nothing when the host leaves the theme to Element Call", () => {
+      const { result } = renderHook(() =>
+        useComponentHostBridge(undefined, undefined, undefined),
+      );
+      const names: (string | undefined)[] = [];
+      result.current.themeChange$.subscribe(({ data }) =>
+        names.push(data.name),
+      );
+      expect(names).toEqual([]);
+    });
+  });
+});
diff --git a/component/host.ts b/component/host.ts
new file mode 100644
index 000000000..c0b2db89b
--- /dev/null
+++ b/component/host.ts
@@ -0,0 +1,201 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * How a host application and the Element Call component talk to each other.
+ *
+ * Inside Element Call the host is a {@link HostBridge}, which carries the
+ * host's requests as rxjs observables because that is what the widget API and
+ * the view models work in. A host should not have to know about rxjs, or agree
+ * with us on a version of it, so a component host sees neither: it implements
+ * plain async callbacks for what Element Call tells it, and makes its own
+ * requests through an imperative handle on the component, the way it would
+ * call `play()` on a video element. This module adapts the one to the other.
+ */
+
+import { type Ref, useEffect, useImperativeHandle } from "react";
+import { ReplaySubject, Subject } from "rxjs";
+
+import {
+  type DeviceMuteRequest,
+  type DeviceMuteState,
+  type HostBridge,
+  type HostRequest,
+} from "../src/HostBridge";
+import { type JoinCallData } from "../src/widget";
+import { useInitial } from "../src/useInitial";
+import { useLatest } from "../src/useLatest";
+
+/**
+ * What Element Call tells the application hosting it as a component.
+ * Everything is optional: a host implements what it wants to hear about.
+ *
+ * Compared by nothing — Element Call always calls whichever one it was most
+ * recently given, so this may be written inline.
+ */
+export interface ElementCallHostBridge {
+  /**
+   * Asks the host to keep Element Call on screen (or stop doing so), so that a
+   * call in progress is not torn down when the user navigates elsewhere.
+   */
+  setAlwaysOnScreen?(alwaysOnScreen: boolean): Promise<void>;
+  /** Tells the host that Element Call has finished loading. */
+  contentLoaded?(): Promise<void>;
+  /** Tells the host that the user has joined the call. */
+  notifyJoined?(): Promise<void>;
+  /** Tells the host that the user has hung up. */
+  notifyHungUp?(): Promise<void>;
+  /** Tells the host the user's current audio and video mute state. */
+  notifyDeviceMute?(state: DeviceMuteState): Promise<void>;
+  /**
+   * Asks the host to close Element Call: to unmount the component. Its
+   * presence is what makes Element Call offer a close button on its error
+   * screens, and leave the host to decide what is shown once a call has ended.
+   * Without it, Element Call shows its own post-call screen, if it has one for
+   * the situation, or nothing.
+   */
+  close?(): Promise<void>;
+  /**
+   * Whether Element Call may send and receive reactions in this room.
+   * Defaults to true.
+   */
+  readonly supportsReactions?: boolean;
+  /**
+   * Whether the user may start unmuted when the intent skips the lobby, so
+   * that they never see their devices before joining. Defaults to false: the
+   * user starts muted and unmutes themselves. A host that chose the intent on
+   * the user's behalf, and is sure they expect to be heard and seen at once,
+   * says so here — as a Matrix client hosting Element Call as a widget does.
+   */
+  readonly allowJoinUnmutedViaIntent?: boolean;
+}
+
+/**
+ * What a host can ask of a mounted Element Call, reached through the
+ * component's `ref`. Each request resolves once Element Call has acted on it,
+ * and rejects if nothing in Element Call is in a position to act: hanging up
+ * when there is no call, say.
+ */
+export interface ElementCallHandle {
+  /**
+   * Joins the call, when Element Call was configured to `preload` and is
+   * waiting to be told to. Says which devices to join with.
+   */
+  join(devices: JoinCallData): Promise<void>;
+  /** Leaves the call. */
+  hangUp(): Promise<void>;
+  /**
+   * Changes the mute state, for whichever of audio and video is given, and
+   * reports the state that results.
+   */
+  setDeviceMute(request: DeviceMuteRequest): Promise<DeviceMuteState>;
+}
+
+/** Hands a request to Element Call and waits for it to be acknowledged. */
+async function request<Data, Reply>(
+  listeners: Subject<HostRequest<Data, Reply>>,
+  what: string,
+  data: Data,
+): Promise<Reply> {
+  if (!listeners.observed)
+    throw new Error(`Nothing in Element Call can ${what} right now`);
+  return await new Promise((resolve) =>
+    listeners.next({ data, reply: resolve }),
+  );
+}
+
+/**
+ * The {@link HostBridge} the rest of Element Call sees, built from what a
+ * component host supplies and wired to the handle it is given.
+ *
+ * The bridge is created once and never changes identity — everything that
+ * depends on it would otherwise restart when the host re-rendered with a new
+ * object — and forwards each call to whatever the host most recently passed.
+ */
+export function useComponentHostBridge(
+  supplied: ElementCallHostBridge | undefined,
+  ref: Ref<ElementCallHandle> | undefined,
+  /** The theme the host wants, or undefined to leave it to Element Call. */
+  theme: string | undefined,
+): HostBridge {
+  const latest = useLatest(supplied ?? {});
+
+  const requests = useInitial(() => ({
+    // The theme is state, not an event: a `theme` prop rather than a request
+    // on the handle. It travels this channel because that is how the rest of
+    // Element Call hears about a host's theme, and replays so that whatever
+    // subscribes after the host has set it — everything, on first render —
+    // still hears the current one.
+    themeChange$: new ReplaySubject<HostRequest<{ name?: string }>>(1),
+    join$: new Subject<HostRequest<JoinCallData>>(),
+    hangUp$: new Subject<HostRequest<Record<string, never>>>(),
+    deviceMute$: new Subject<HostRequest<DeviceMuteRequest, DeviceMuteState>>(),
+  }));
+
+  useEffect(() => {
+    if (theme !== undefined)
+      requests.themeChange$.next({ data: { name: theme }, reply: () => {} });
+  }, [requests, theme]);
+
+  const bridge = useInitial((): HostBridge => ({
+    setAlwaysOnScreen: async (alwaysOnScreen) => {
+      await latest.current.setAlwaysOnScreen?.(alwaysOnScreen);
+    },
+    contentLoaded: async () => {
+      await latest.current.contentLoaded?.();
+    },
+    notifyJoined: async () => {
+      await latest.current.notifyJoined?.();
+    },
+    notifyHungUp: async () => {
+      await latest.current.notifyHungUp?.();
+    },
+    notifyDeviceMute: async (state) => {
+      await latest.current.notifyDeviceMute?.(state);
+    },
+    // Whether these exist is itself information, so they are read through
+    // rather than wrapped unconditionally
+    get close() {
+      const close = latest.current.close;
+      return close === undefined
+        ? undefined
+        : async (): Promise<void> => await close();
+    },
+    // Not offered to a component host: the client it hands over holds the
+    // credentials to fetch media itself. A widget's client does not, which
+    // is what the internal bridge's `downloadMedia` is for.
+    get supportsReactions(): boolean {
+      return latest.current.supportsReactions ?? true;
+    },
+    get allowJoinUnmutedViaIntent(): boolean {
+      return latest.current.allowJoinUnmutedViaIntent ?? false;
+    },
+    // Whatever the host says or does not say, the account is its own: it
+    // signed the user in and handed us the client. So Element Call never
+    // offers to edit the profile from inside a component.
+    supportsProfileChanges: false,
+    ...requests,
+  }));
+
+  useImperativeHandle(
+    ref,
+    (): ElementCallHandle => ({
+      join: async (devices) =>
+        await request(requests.join$, "join a call", devices),
+      hangUp: async () => await request(requests.hangUp$, "hang up", {}),
+      setDeviceMute: async (muteRequest) =>
+        await request(
+          requests.deviceMute$,
+          "change the mute state",
+          muteRequest,
+        ),
+    }),
+    [requests],
+  );
+
+  return bridge;
+}
diff --git a/component/index.tsx b/component/index.tsx
new file mode 100644
index 000000000..b3f04e00c
--- /dev/null
+++ b/component/index.tsx
@@ -0,0 +1,358 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * EXPERIMENTAL
+ *
+ * Element Call as a React component, for an application that wants to show a
+ * call inside itself rather than in an iframe.
+ *
+ * The host supplies the client and says which room to call in; Element Call
+ * supplies the call. Everything it would otherwise take from the page it is on
+ * — the URL, the document body, a Matrix session of its own — comes from the
+ * host instead, or is confined to the container it is mounted in.
+ */
+
+// The design tokens, fonts and element defaults every Element Call stylesheet
+// builds on. Written for a page, they speak of `html`, `body` and bare
+// elements; the component build confines them, and every other stylesheet in
+// this bundle, to the root element below (see build/scopeStylesToRoot.ts), so
+// that the host's document is left as it was.
+//
+// Where these land relative to the component stylesheets is the bundler's
+// choice — the standalone app puts them first, this build puts them in the
+// middle — so nothing in base.css may depend on winning or losing against a
+// component's own rules at equal specificity. It currently does not: what it
+// declares unlayered is custom properties on Element Call's root, which
+// components inherit rather than compete with, and everything from Compound
+// sits in a `@layer`, which loses to unlayered rules either way.
+import "../src/base.css";
+
+import {
+  type FC,
+  type JSX,
+  type ReactNode,
+  type Ref,
+  useEffect,
+  useLayoutEffect,
+  useMemo,
+  useRef,
+  useState,
+} from "react";
+import { type MatrixClient } from "matrix-js-sdk";
+import { logger } from "matrix-js-sdk/lib/logger";
+import { I18nextProvider } from "react-i18next";
+import { TooltipProvider } from "@vector-im/compound-web";
+import { ErrorBoundary } from "@sentry/react";
+import { shouldPolyfill as shouldPolyfillSegmenter } from "@formatjs/intl-segmenter/should-polyfill";
+import { shouldPolyfill as shouldPolyfillDurationFormat } from "@formatjs/intl-durationformat/should-polyfill.js";
+
+import LanguageDetector from "i18next-browser-languagedetector";
+
+import EN from "../locales/en/app.json";
+import { CallView } from "../src/room/CallView";
+import { ErrorPage } from "../src/FullScreenView";
+import { ClientProvider } from "../src/ClientContext";
+import { HostBridgeProvider } from "../src/HostBridge";
+import { RootElementProvider, useRootElement } from "../src/RootElementContext";
+import {
+  configurationForIntent,
+  componentProperties,
+  type UrlConfiguration,
+  type UrlParams,
+  UrlParamsProvider,
+  type UrlProperties,
+  UserIntent,
+  useUrlParams,
+} from "../src/UrlParams";
+import { MediaDevicesContext } from "../src/MediaDevicesContext";
+import { MediaDevices } from "../src/state/MediaDevices";
+import { ObservableScope } from "../src/state/ObservableScope";
+import { ProcessorProvider } from "../src/livekit/TrackProcessorContext";
+import { Config } from "../src/config/Config";
+import { type ConfigOptions } from "../src/config/ConfigOptions";
+import { i18n } from "../src/utils/i18n";
+import { useTheme } from "../src/useTheme";
+import { useStableValue } from "../src/useStableValue";
+import styles from "./ElementCall.module.css";
+import {
+  type ElementCallHandle,
+  type ElementCallHostBridge,
+  useComponentHostBridge,
+} from "./host";
+import { supportedLanguages, translationsBackend } from "./localization";
+
+// The languages Element Call can be shown in
+export { supportedLanguages } from "./localization";
+
+// How the host and Element Call talk to each other, and what they say
+export { type ElementCallHandle, type ElementCallHostBridge } from "./host";
+export {
+  type DeviceMuteRequest,
+  type DeviceMuteState,
+} from "../src/HostBridge";
+export { type JoinCallData } from "../src/widget";
+// The deployment-wide configuration, as distinct from ElementCallConfiguration
+// above, which is per call
+export { type ConfigOptions } from "../src/config/ConfigOptions";
+// The values that appear in ElementCallConfiguration and in the intent
+export {
+  BackgroundStyle,
+  HeaderStyle,
+  UserIntent,
+  type UrlConfiguration,
+} from "../src/UrlParams";
+
+/**
+ * How Element Call should behave. Everything is optional; anything left out
+ * takes the default that {@link ElementCallProps.intent} implies.
+ *
+ * This is the behaviour a widget can be configured with through its URL, plus
+ * the one fact about the call a host has a say in here, the background. The
+ * rest of what a widget's URL carries — who the user is, how to reach the
+ * homeserver, where to report analytics, the shared secret of a room that is
+ * encrypted with one — a component host supplies by other routes, or not at
+ * all; and what can change while the call is running, the theme and the
+ * language, is a prop of its own.
+ */
+export type ElementCallConfiguration = Partial<UrlConfiguration> &
+  Partial<Pick<UrlProperties, "background">>;
+
+export interface ElementCallProps {
+  /**
+   * The client to place the call with. Element Call does not authenticate
+   * anyone or manage a session of its own; this one is the host's.
+   */
+  client: MatrixClient;
+  /** The room to call in. The host's client must already know about it. */
+  roomId: string;
+  /**
+   * What the user asked for — whether they started the call or joined one that
+   * was already running, and whether it is a call in a group or a DM. Element
+   * Call decides what each of those means: whether to show the lobby first,
+   * whether to ring, and so on.
+   *
+   * Defaults to joining an existing group call, which is the most conservative
+   * reading, but a host that knows which button the user pressed should say so.
+   */
+  intent?: UserIntent;
+  /**
+   * How Element Call should behave, overriding whatever {@link intent} implies.
+   * A host that finds itself setting a lot of these probably wants a different
+   * intent instead.
+   *
+   * Compared by value, so it is fine to write this inline; only a change to
+   * what it says restarts anything.
+   */
+  config?: ElementCallConfiguration;
+  /**
+   * What Element Call tells the host while the call is running: that the user
+   * has joined or hung up, that it would like to be kept on screen, and so on.
+   * Without one, Element Call assumes nobody is listening.
+   */
+  hostBridge?: ElementCallHostBridge;
+  /**
+   * What the host tells Element Call: to hang up, to mute, to join. Available
+   * once the component has rendered.
+   */
+  ref?: Ref<ElementCallHandle>;
+  /**
+   * The theme to show Element Call in, `light` or `dark`. Left out, Element
+   * Call picks. Changes take effect at once, and cost nothing else.
+   */
+  theme?: string;
+  /**
+   * The language to show Element Call in, as a BCP 47 tag: one of
+   * {@link supportedLanguages}, or something that falls back to one (`de-AT`
+   * to `de`). Left out, the browser's language is used.
+   *
+   * Translations are one thing shared by every Element Call on the page, so
+   * the most recently set language wins for all of them.
+   */
+  language?: string;
+}
+
+/**
+ * Prepares the things Element Call needs before it can be shown: translations,
+ * `Intl` polyfills for older browsers, and its configuration.
+ *
+ * Await this once, before rendering {@link ElementCall}.
+ */
+export async function initializeElementCall(
+  config: ConfigOptions = {},
+): Promise<void> {
+  const polyfills: Promise<unknown>[] = [];
+  if (shouldPolyfillSegmenter())
+    polyfills.push(import("@formatjs/intl-segmenter/polyfill-force"));
+  if (shouldPolyfillDurationFormat())
+    polyfills.push(import("@formatjs/intl-durationformat/polyfill-force.js"));
+  await Promise.all(polyfills);
+
+  Config.initWith(config);
+  await i18n
+    .use(translationsBackend)
+    .use(new LanguageDetector())
+    .init({
+      fallbackLng: "en",
+      defaultNS: "app",
+      keySeparator: ".",
+      nsSeparator: false,
+      pluralSeparator: "_",
+      contextSeparator: "|",
+      supportedLngs: [...supportedLanguages],
+      interpolation: { escapeValue: false },
+      // English is bundled in, so the fallback never has to be loaded; every
+      // other language arrives from the backend when first asked for.
+      partialBundledLanguages: true,
+      resources: { en: { app: EN } },
+      detection: {
+        // The browser's language, until the host says otherwise through the
+        // `language` prop. Nothing is remembered: the choice is the host's.
+        order: ["navigator"],
+        caches: [],
+      },
+    });
+}
+
+/** Applies the theme and background to the container, before it is painted. */
+const Decoration: FC<{ children: JSX.Element }> = ({ children }) => {
+  useTheme();
+  const { background } = useUrlParams();
+  const rootElement = useRootElement();
+  useLayoutEffect(() => {
+    rootElement.setAttribute("data-background", background);
+  }, [rootElement, background]);
+  return children;
+};
+
+export const ElementCall: FC<ElementCallProps> = ({
+  client,
+  roomId,
+  intent = UserIntent.JoinExistingCall,
+  config,
+  hostBridge: suppliedHostBridge,
+  ref,
+  theme,
+  language,
+}): ReactNode => {
+  const hostBridge = useComponentHostBridge(suppliedHostBridge, ref, theme);
+
+  useEffect(() => {
+    if (language !== undefined)
+      i18n
+        .changeLanguage(language)
+        .catch((e) => logger.error(`Could not switch to ${language}`, e));
+  }, [language]);
+
+  // The container is what Element Call decorates and portals into, so nothing
+  // inside can render until we have it.
+  const [container, setContainer] = useState<HTMLDivElement | null>(null);
+
+  // Element Call has no URL of its own to read any of this from, and the
+  // host's URL is not Element Call's business, so the defaults come from the
+  // intent with the host's wishes over the top.
+  //
+  // Everything downstream — the mute state, the call view model and with it
+  // the media connection — is keyed on the identity of this object, so it has
+  // to be stable for as long as its contents are. A host writing `config`
+  // inline would otherwise tear the call down on every render.
+  const stableConfig = useStableValue(config);
+  const params = useMemo(
+    (): UrlParams => ({
+      ...componentProperties,
+      roomId,
+      ...configurationForIntent(intent),
+      ...stableConfig,
+    }),
+    [roomId, intent, stableConfig],
+  );
+
+  // Created in an effect so that the scope it lives in ends when the component
+  // is unmounted (or these options change), rather than keeping its device
+  // observers running for the rest of the page's life. Null until then, which
+  // is one render.
+  const { controlledAudioDevices, callIntent } = params;
+  const [mediaDevices, setMediaDevices] = useState<MediaDevices | null>(null);
+  useEffect(() => {
+    const scope = new ObservableScope();
+    setMediaDevices(
+      new MediaDevices(scope, { controlledAudioDevices, callIntent }),
+    );
+    return (): void => {
+      setMediaDevices(null);
+      scope.end();
+    };
+  }, [controlledAudioDevices, callIntent]);
+
+  const room = client.getRoom(roomId);
+  const rtcSession = useMemo(
+    () => (room === null ? null : client.matrixRTC.getRoomSession(room)),
+    [client, room],
+  );
+
+  if (rtcSession === null)
+    logger.error(
+      `Element Call was asked to call in ${roomId}, which its host's client does not know about`,
+    );
+
+  // Everything the call needs is in hand once these exist, and the first
+  // render with them is where the call itself appears: the moment the host
+  // is told that Element Call has loaded, as the widget tells its client once
+  // its own initialisation is over. Once per mount, however often the pieces
+  // are later swapped out.
+  const ready =
+    container !== null && rtcSession !== null && mediaDevices !== null;
+  const announcedLoaded = useRef(false);
+  useEffect(() => {
+    if (!ready || announcedLoaded.current) return;
+    announcedLoaded.current = true;
+    hostBridge
+      .contentLoaded()
+      .catch((e) => logger.error("Could not tell the host we had loaded", e));
+  }, [ready, hostBridge]);
+
+  return (
+    <I18nextProvider i18n={i18n}>
+      <HostBridgeProvider value={hostBridge}>
+        <UrlParamsProvider value={params}>
+          <div ref={setContainer} className={styles.root}>
+            {ready && (
+              <RootElementProvider value={container}>
+                {/* Whatever goes wrong in here is shown in here. Left to
+                  propagate, an error would unmount the host's own tree. */}
+                <ErrorBoundary
+                  fallback={(error) => <ErrorPage error={error} />}
+                  // A broken call should not hold the host on screen
+                  onError={() => void hostBridge.setAlwaysOnScreen(false)}
+                >
+                  <Decoration>
+                    <TooltipProvider>
+                      <ClientProvider client={client}>
+                        <MediaDevicesContext value={mediaDevices}>
+                          <ProcessorProvider>
+                            <CallView
+                              client={client}
+                              rtcSession={rtcSession}
+                              isPasswordlessUser={false}
+                              confineToRoom={params.confineToRoom}
+                              preload={params.preload}
+                              skipLobby={params.skipLobby}
+                            />
+                          </ProcessorProvider>
+                        </MediaDevicesContext>
+                      </ClientProvider>
+                    </TooltipProvider>
+                  </Decoration>
+                </ErrorBoundary>
+              </RootElementProvider>
+            )}
+          </div>
+        </UrlParamsProvider>
+      </HostBridgeProvider>
+    </I18nextProvider>
+  );
+};
diff --git a/component/localization.test.ts b/component/localization.test.ts
new file mode 100644
index 000000000..fae1c7065
--- /dev/null
+++ b/component/localization.test.ts
@@ -0,0 +1,46 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test } from "vitest";
+
+import { supportedLanguages, translationsBackend } from "./localization";
+
+const read = async (
+  language: string,
+  namespace = "app",
+): Promise<Record<string, unknown>> =>
+  await new Promise((resolve, reject) =>
+    translationsBackend.read(language, namespace, (error, data) => {
+      if (error) reject(error);
+      else resolve(data as Record<string, unknown>);
+    }),
+  );
+
+describe("component translations", () => {
+  test("offer every language in locales/, tagged as its directory is", () => {
+    expect(supportedLanguages).toContain("en");
+    expect(supportedLanguages).toContain("de");
+    expect(supportedLanguages).toContain("zh-Hans");
+    expect(new Set(supportedLanguages).size).toBe(supportedLanguages.length);
+  });
+
+  test("load a language's translations on demand", async () => {
+    const de = await read("de");
+    expect(de).toHaveProperty("action");
+    expect(de).not.toEqual(await read("en"));
+  });
+
+  test("refuse a language there are no translations for", async () => {
+    await expect(read("xx")).rejects.toThrow("No app translations for xx");
+  });
+
+  test("refuse a namespace there are no translations for", async () => {
+    await expect(read("en", "other")).rejects.toThrow(
+      "No other translations for en",
+    );
+  });
+});
diff --git a/component/localization.ts b/component/localization.ts
new file mode 100644
index 000000000..b64172818
--- /dev/null
+++ b/component/localization.ts
@@ -0,0 +1,55 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * Translations for Element Call as a component.
+ *
+ * The standalone app fetches its locale files at runtime from URLs its own
+ * build emits, which a host serving the library from somewhere else could not
+ * resolve. The component instead has the bundler split every locale into a
+ * chunk of its own, loaded the first time its language is asked for; English,
+ * the fallback, is bundled in so that the first paint never waits for it.
+ */
+
+import { type BackendModule, type ResourceKey } from "i18next";
+
+import { languageOfLocalePath } from "../src/utils/i18n";
+
+/** Every locale, as a lazily imported module. */
+const translations = import.meta.glob<{ default: ResourceKey }>(
+  "../locales/*/app.json",
+);
+
+/**
+ * The languages Element Call can be shown in, as BCP 47 tags — `en`, `de`,
+ * `zh-Hans` and so on. A language that is not one of these falls back to its
+ * base language where there is one (`de-AT` to `de`), and to English otherwise.
+ */
+export const supportedLanguages: readonly string[] = [
+  ...new Set(Object.keys(translations).map(languageOfLocalePath)),
+];
+
+/** Loads translations on demand. */
+export const translationsBackend: BackendModule = {
+  type: "backend",
+  init(): void {},
+  read(language: string, namespace: string, callback): void {
+    const load = translations[`../locales/${language}/${namespace}.json`];
+    if (load === undefined) {
+      callback(new Error(`No ${namespace} translations for ${language}`), null);
+      return;
+    }
+    load().then(
+      (module) => callback(null, module.default),
+      (error: unknown) =>
+        callback(
+          error instanceof Error ? error : new Error(String(error)),
+          null,
+        ),
+    );
+  },
+};
diff --git a/component/package.json b/component/package.json
new file mode 100644
index 000000000..9ed81e02a
--- /dev/null
+++ b/component/package.json
@@ -0,0 +1,42 @@
+{
+  "name": "@element-hq/element-call-component",
+  "version": "0.0.0",
+  "description": "Element Call as a React component. Consumed straight from the repository as a git dependency (github:element-hq/element-call#<ref>&path:/component): the host's package manager runs `prepare`, which builds `dist/`.",
+  "license": "SEE LICENSE IN ../README.md",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/element-hq/element-call",
+    "directory": "component"
+  },
+  "type": "module",
+  "devEngines": {
+    "packageManager": {
+      "name": "pnpm"
+    }
+  },
+  "files": [
+    "dist"
+  ],
+  "main": "./dist/element-call.js",
+  "module": "./dist/element-call.js",
+  "types": "./dist/types/component/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/types/component/index.d.ts",
+      "default": "./dist/element-call.js"
+    },
+    "./style.css": "./dist/element-call.css"
+  },
+  "sideEffects": [
+    "*.css"
+  ],
+  "scripts": {
+    "prepare": "cd .. && pnpm install --frozen-lockfile && pnpm build:component"
+  },
+  "peerDependencies": {
+    "livekit-client": "^2.18.1",
+    "matrix-js-sdk": "*",
+    "react": "^19",
+    "react-dom": "^19"
+  }
+}
diff --git a/component/pnpm-lock.yaml b/component/pnpm-lock.yaml
new file mode 100644
index 000000000..490c2e4fa
--- /dev/null
+++ b/component/pnpm-lock.yaml
@@ -0,0 +1,9 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: false
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .: {}
diff --git a/component/pnpm-workspace.yaml b/component/pnpm-workspace.yaml
new file mode 100644
index 000000000..d6c26ac66
--- /dev/null
+++ b/component/pnpm-workspace.yaml
@@ -0,0 +1,14 @@
+# Makes `component/` a pnpm project of its own rather than a directory inside
+# the repository's workspace. That matters when a host installs the component
+# straight from this repository (`github:element-hq/element-call#…&path:/component`):
+# pnpm prepares such a dependency by running `pnpm install` in this directory,
+# and only a project root gets its `prepare` script (see package.json) run, which
+# is what builds `dist/`. Inside the repository's own workspace the install
+# would silently target the repository instead and build nothing.
+#
+# Consequence for development: pnpm commands run from within this directory see
+# this project, not the repository; run them from the repository root.
+
+# Nothing to install here: the peers in package.json are the host's, and the
+# build runs against the repository's own node_modules (see `prepare`).
+autoInstallPeers: false
diff --git a/component/tsconfig.build.json b/component/tsconfig.build.json
new file mode 100644
index 000000000..18af65d84
--- /dev/null
+++ b/component/tsconfig.build.json
@@ -0,0 +1,20 @@
+{
+  // Declaration output for the component package (`pnpm build:component:types`).
+  // The root tsconfig only type-checks; this one emits `.d.ts` files, and nothing
+  // else, for everything the component's entry point reaches. The layout under
+  // `dist/types` mirrors the repository (`component/index.d.ts`, `src/…`), which
+  // is what `package.json` points its `types` at.
+  "extends": "../tsconfig.json",
+  "compilerOptions": {
+    "noEmit": false,
+    "emitDeclarationOnly": true,
+    "declaration": true,
+    "declarationMap": false,
+    "rootDir": "..",
+    "outDir": "./dist/types"
+  },
+  // The entry point, plus the ambient declarations (CSS modules, `?react` SVGs,
+  // `import.meta.env`, …) that the sources it reaches rely on.
+  "include": ["./index.tsx", "../src/@types/*.d.ts"],
+  "exclude": []
+}
diff --git a/docs/README.md b/docs/README.md
index 56c96a6ca..c4b60c2fd 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -3,6 +3,7 @@
 This folder contains documentation for setup, usage, and development of Element Call.
 
 - [Embedded vs standalone mode](./embedded_standalone.md)
+- [Element Call as a React component (experimental)](../README.md#element-call-as-a-component-experimental)
 - [Url format and parameters](./url_params.md)
 - [Global JS controls](./controls.md)
 - [MatrixRTC modes](./matrix_rtc_modes.md)
diff --git a/docs/embedded_standalone.md b/docs/embedded_standalone.md
index 456ce120a..a85ca6eab 100644
--- a/docs/embedded_standalone.md
+++ b/docs/embedded_standalone.md
@@ -3,6 +3,9 @@
 Element Call is available as two different packages: Full Package and Embedded Package.
 
 The Full Package is designed for standalone use, while the Embedded Package is designed for widget mode only.
+There is also an experimental third option, a build of Element Call as a React component for applications
+that want to render a call inside their own page rather than in an iframe; see
+[Element Call as a component](../README.md#element-call-as-a-component-experimental) in the README.
 
 The table below provides a comparison of the two packages:
 
diff --git a/knip.ts b/knip.ts
index 8412d5915..d9de80c8c 100644
--- a/knip.ts
+++ b/knip.ts
@@ -9,7 +9,13 @@ import { type KnipConfig } from "knip";
 
 export default {
   vite: {
-    config: ["vite.config.ts", "vite-embedded.config.ts", "vite-sdk.config.ts"],
+    config: [
+      "vite.config.ts",
+      "vite-embedded.config.ts",
+      "vite-sdk.config.ts",
+      "vite-component.config.ts",
+      "vite-component-dev.config.ts",
+    ],
   },
   entry: ["src/main.tsx", "eslint/index.js", "i18next.config.ts"],
   ignoreBinaries: [
diff --git a/package.json b/package.json
index bb28b67cd..90e5e0394 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
     "dev": "pnpm dev:full",
     "dev:full": "vite",
     "dev:embedded": "vite --config vite-embedded.config.js",
+    "dev:component": "vite --config vite-component-dev.config.ts",
     "build": "pnpm build:full",
     "build:full": "NODE_OPTIONS=--max-old-space-size=16384 vite build",
     "build:full:production": "pnpm build:full",
@@ -16,13 +17,19 @@
     "build:sdk:development": "pnpm build:sdk --mode development",
     "build:sdk": "pnpm build:full --config vite-sdk.config.js",
     "build:sdk:production": "pnpm build:sdk",
+    "build:component": "pnpm build:component:js && pnpm build:component:types",
+    "build:component:js": "pnpm build:full --config vite-component.config.js",
+    "build:component:types": "tsc -p component/tsconfig.build.json",
+    "build:component:production": "pnpm build:component",
+    "build:component:development": "pnpm build:component:js --mode development && pnpm build:component:types",
     "serve": "vite preview",
     "format": "oxfmt",
     "format:check": "oxfmt --check; rc=$?; [[ $rc -ne 0 ]] && printf '\\033[46;30m INFO \\033[0m To fix, run: pnpm format\\n' >&2; exit $rc",
-    "lint": "pnpm lint:types && pnpm lint:oxlint && pnpm lint:knip",
-    "lint:oxlint": "oxlint src playwright",
-    "lint:oxlint-fix": "oxlint --fix src playwright",
+    "lint": "pnpm lint:types && pnpm lint:oxlint && pnpm lint:knip && pnpm lint:externals",
+    "lint:oxlint": "oxlint src component playwright",
+    "lint:oxlint-fix": "oxlint --fix src component playwright",
     "lint:knip": "knip",
+    "lint:externals": "node scripts/check-component-externals.mjs",
     "lint:types": "tsc",
     "i18n": "npx i18next-cli extract",
     "i18n:check": "npx i18next-cli extract --ci",
@@ -107,6 +114,7 @@
     "pako": "^2.0.4",
     "postcss": "^8.4.41",
     "postcss-preset-env": "^10.0.0",
+    "postcss-selector-parser": "^7.1.1",
     "posthog-js": "1.408.2",
     "qrcode": "^1.5.4",
     "react": "19",
diff --git a/playwright.config.ts b/playwright.config.ts
index 85e65e13f..e6dcc5249 100644
--- a/playwright.config.ts
+++ b/playwright.config.ts
@@ -11,6 +11,8 @@ import { join } from "path";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 
+import { COMPONENT_HARNESS_URL } from "./playwright/component/harness.ts";
+
 const baseURL = process.env.USE_DOCKER
   ? "http://localhost:8080"
   : "https://localhost:3000";
@@ -84,6 +86,11 @@ export default defineConfig({
             // enumerateDevices work on CI runners without real hardware.
             "media.navigator.streams.fake": true,
             "media.navigator.permission.disabled": true,
+            // Vite serves HTTPS over HTTP/2, and Firefox intermittently stalls
+            // on Node's HTTP/2 server with a page that never finishes loading
+            // (one run in five or so, locally). Every server in the suite
+            // still speaks HTTP/1.1, so nothing is lost by insisting on it.
+            "network.http.http2.enabled": false,
           },
         },
       },
@@ -115,14 +122,29 @@ export default defineConfig({
   ],
 
   /* Run your local dev server before starting the tests */
-  webServer: {
-    command: "./scripts/playwright-webserver-command.sh",
-    url: baseURL,
-    reuseExistingServer: !process.env.CI,
-    ignoreHTTPSErrors: true,
-    gracefulShutdown: {
-      signal: "SIGTERM",
-      timeout: 500,
+  webServer: [
+    {
+      command: "./scripts/playwright-webserver-command.sh",
+      url: baseURL,
+      reuseExistingServer: !process.env.CI,
+      ignoreHTTPSErrors: true,
+      gracefulShutdown: {
+        signal: "SIGTERM",
+        timeout: 500,
+      },
     },
-  },
+    {
+      // The harness that embeds Element Call as a component. Always a Vite dev
+      // server, whether or not the app itself is being served from Docker,
+      // since there is nothing to build: it is a development page only.
+      command: "pnpm dev:component",
+      url: COMPONENT_HARNESS_URL,
+      reuseExistingServer: !process.env.CI,
+      ignoreHTTPSErrors: true,
+      gracefulShutdown: {
+        signal: "SIGTERM",
+        timeout: 500,
+      },
+    },
+  ],
 });
diff --git a/playwright/component/component-call.spec.ts b/playwright/component/component-call.spec.ts
new file mode 100644
index 000000000..e4376ddb2
--- /dev/null
+++ b/playwright/component/component-call.spec.ts
@@ -0,0 +1,285 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, type Locator, type Page, test } from "@playwright/test";
+
+import {
+  createUserAndRoom,
+  expectWithin,
+  resizeContainer,
+  startHarness,
+} from "./harness.ts";
+import { SpaHelpers } from "../spa-helpers.ts";
+
+/**
+ * Element Call embedded as a React component, driven through the development
+ * harness in `component/dev`.
+ *
+ * What these cover that the widget tests cannot is everything that follows from
+ * sharing a page with a host: whether Element Call stays inside the space it
+ * was given, and whether two of it can exist at once. As a widget, the iframe
+ * guaranteed both.
+ */
+
+// Each test signs in twice, sets up crypto twice and syncs twice before
+// anything is on screen, and then waits for media to connect; the waits below
+// are sized for that, so the tests have to be too
+test.describe.configure({ timeout: 180_000 });
+
+/** The settings button, whichever of the two the footer is currently showing. */
+function settingsButton(pane: Locator): Locator {
+  return pane
+    .getByTestId("settings-bottom-left")
+    .or(pane.getByTestId("settings-bottom-center"))
+    .filter({ visible: true })
+    .first();
+}
+
+test("holds a call between two components on one page", async ({ page }) => {
+  const { username, roomId } = await createUserAndRoom("twocomponents");
+  const panes = await startHarness(page, username, roomId);
+
+  // Each component shows a lobby of its own, and neither has joined anything
+  // just by being rendered
+  for (const index of [0, 1])
+    await expect(panes.nth(index).getByTestId("lobby_joinCall")).toBeVisible({
+      timeout: 60_000,
+    });
+
+  for (const index of [0, 1])
+    await panes.nth(index).getByTestId("lobby_joinCall").click();
+
+  // Two devices of one account, so each component should see itself and the
+  // other. This is the part that proves two Element Calls in one page are two
+  // calls, and not one shared thing wearing two hats.
+  for (const index of [0, 1])
+    await expect(panes.nth(index).getByTestId("videoTile")).toHaveCount(2, {
+      timeout: 60_000,
+    });
+});
+
+test("keeps its modals inside the container it was given", async ({ page }) => {
+  const { username, roomId } = await createUserAndRoom("containment");
+  const panes = await startHarness(page, username, roomId);
+  const pane = panes.first();
+  const container = pane.getByTestId("call-container");
+
+  // In the flat container the harness gives it by default, Element Call hides
+  // its controls a few seconds after the call starts, as it would in a flat
+  // window. A full-size container keeps them on screen to be clicked.
+  await resizeContainer(container, { width: 900, height: 640 });
+  await pane.getByTestId("lobby_joinCall").click({ timeout: 60_000 });
+  await expect(pane.getByTestId("footer-container")).toBeVisible({
+    timeout: 60_000,
+  });
+
+  // Both of these are positioned `fixed`, and were centred on the window
+  // rather than the container until it was made a containing block. The
+  // settings dialog spilled over the host's interface; the reaction picker sat
+  // at 82vh, which put it below the container entirely and so out of sight.
+  await settingsButton(pane).click();
+  await expectWithin(pane.getByRole("dialog"), container);
+  await pane.getByTestId("modal_close").click();
+
+  await pane.getByRole("button", { name: "Reactions" }).click();
+  await expectWithin(
+    pane.getByRole("dialog", { name: "Pick reaction" }),
+    container,
+  );
+});
+
+test("keeps the call inside the container, wherever the host put it", async ({
+  page,
+}) => {
+  const { username, roomId } = await createUserAndRoom("tileswithin");
+  const panes = await startHarness(page, username, roomId);
+  const pane = panes.first();
+  const container = pane.getByTestId("call-container");
+
+  // Large enough for the layout switch to be offered
+  await resizeContainer(container, { width: 900, height: 640 });
+  await pane.getByTestId("lobby_joinCall").click({ timeout: 60_000 });
+  await expect(pane.getByTestId("footer-container")).toBeVisible({
+    timeout: 60_000,
+  });
+
+  // The spotlight layout draws its tile in the fixed grid, which is positioned
+  // against Element Call's root rather than laid out in flow. The harness puts
+  // the container below a header of its own, so a grid offset measured from
+  // the top of the page instead of from the root would land the tile on top of
+  // the footer and out of the bottom of the container.
+  await pane.getByRole("radio", { name: "Spotlight" }).check();
+  const tile = pane.getByTestId("videoTile").first();
+  await expect(tile).toBeVisible({ timeout: 60_000 });
+  await expectWithin(tile, container);
+});
+
+test("leaves the host's own page unstyled", async ({ page }) => {
+  const { username, roomId } = await createUserAndRoom("hoststyles");
+  const panes = await startHarness(page, username, roomId);
+  await expect(panes.first().getByTestId("lobby_joinCall")).toBeVisible({
+    timeout: 60_000,
+  });
+
+  // Element Call's stylesheet is written for a page of its own: normalize.css
+  // gives `html` a line height, Compound gives `body` its font and feature
+  // settings, and the design tokens live on `:root`. None of that may reach the
+  // host's document — the harness sets none of these itself, so anything other
+  // than the browser's defaults here came from us.
+  const host = await page.evaluate(() => {
+    const html = getComputedStyle(document.documentElement);
+    const body = getComputedStyle(document.body);
+    return {
+      lineHeight: html.lineHeight,
+      fontFeatureSettings: body.fontFeatureSettings,
+      token: html.getPropertyValue("--cpd-color-text-primary"),
+    };
+  });
+  expect(host).toEqual({
+    lineHeight: "normal",
+    fontFeatureSettings: "normal",
+    token: "",
+  });
+
+  // While inside the container, the same rules do apply
+  const root = panes.first().locator("[data-element-call-root]");
+  await expect(root).toHaveCSS("font-feature-settings", /"kern"/);
+});
+
+test("tells its host what it is doing", async ({ page }) => {
+  const { username, roomId } = await createUserAndRoom("hostbridge");
+  const panes = await startHarness(page, username, roomId);
+  const pane = panes.first();
+  const log = page.getByTestId("bridge-log");
+
+  // Every component reports to its host through the bridge, whether that host
+  // is a widget container or an application embedding it directly
+  await expect(log).toContainText("contentLoaded", { timeout: 60_000 });
+
+  await pane.getByTestId("lobby_joinCall").click({ timeout: 60_000 });
+  await expect(log).toContainText("notifyJoined", { timeout: 60_000 });
+  await expect(log).toContainText("setAlwaysOnScreen(true)", {
+    timeout: 60_000,
+  });
+
+  // And takes instructions back: the host asking for a mute should come back
+  // as the component reporting the new state
+  await pane.getByRole("button", { name: "Mute" }).click();
+  await expect(log).toContainText("notifyDeviceMute(audio: false", {
+    timeout: 30_000,
+  });
+});
+
+test("lays itself out for the space it is given, not the page", async ({
+  page,
+}) => {
+  const { username, roomId } = await createUserAndRoom("containersize");
+  const panes = await startHarness(page, username, roomId);
+  const pane = panes.first();
+  const container = pane.getByTestId("call-container");
+  const call = pane.locator("[data-layout]");
+
+  await pane.getByTestId("lobby_joinCall").click({ timeout: 60_000 });
+  await expect(call).toBeVisible({ timeout: 60_000 });
+  await expect(call).not.toHaveAttribute("data-layout", "pip");
+
+  // As a widget, Element Call's container and its window were one and the same:
+  // a host wanting a picture-in-picture made the iframe small, and Element Call
+  // saw the window shrink. A component gets no such signal from the window,
+  // which stays as large as it ever was; only the container changes.
+  await resizeContainer(container, { width: 300, height: 300 });
+  await expect(call).toHaveAttribute("data-layout", "pip");
+
+  await resizeContainer(container, { width: 900, height: 700 });
+  await expect(call).not.toHaveAttribute("data-layout", "pip");
+});
+
+/**
+ * The shape of a call at whatever size it has been given: the layout it chose,
+ * how much of the height the tile and the footer take, and which controls the
+ * footer shows. Two calls with the same shape look the same, participants aside.
+ */
+async function callShape(scope: Page | Locator): Promise<{
+  layout: string | null;
+  tileHeight: number;
+  footerHeight: number;
+  buttons: (string | null)[];
+}> {
+  const call = scope.locator("[data-layout]");
+  const footer = scope.getByTestId("footer-container");
+  await expect(footer).toBeVisible();
+  // The tile arrives with the media connection, which can take a while
+  const tile = scope.getByTestId("videoTile").first();
+  await expect(tile).toBeVisible({ timeout: 60_000 });
+  const tileBox = (await tile.boundingBox())!;
+  const footerBox = (await footer.boundingBox())!;
+  // Buttons and switches alike: the mute controls are switches
+  const buttons = await footer
+    .locator("button")
+    .filter({ visible: true })
+    .evaluateAll((elements) =>
+      elements.map((element) => element.getAttribute("aria-label")),
+    );
+  return {
+    layout: await call.getAttribute("data-layout"),
+    tileHeight: Math.round(tileBox.height),
+    footerHeight: Math.round(footerBox.height),
+    buttons,
+  };
+}
+
+test("looks the same in a small container as in a small window", async ({
+  page,
+  browser,
+}) => {
+  // Two calls to set up, one of them through the harness's two logins
+  test.setTimeout(300_000);
+  const size = { width: 300, height: 300 };
+
+  // The reference is Element Call owning a window of that size, which is what
+  // a mobile app's webview or a browser's picture-in-picture gives it, and
+  // what its small-window styling was written for.
+  // No permissions to grant: each browser is launched with fake media that is
+  // handed out without asking (see playwright.config.ts), and Firefox rejects
+  // a request for `camera` or `microphone` outright
+  const referenceContext = await browser.newContext({
+    viewport: size,
+    ignoreHTTPSErrors: true,
+  });
+  const referencePage = await referenceContext.newPage();
+  await referencePage.goto("/");
+  await SpaHelpers.createCall(referencePage, "Reference", "smallwindow", true);
+  const reference = await callShape(referencePage);
+  await referencePage.screenshot({
+    path: test.info().outputPath("small-window.png"),
+  });
+
+  // The component gets a container of that size, in a window that is far larger
+  const { username, roomId } = await createUserAndRoom("smallcontainer");
+  const panes = await startHarness(page, username, roomId);
+  const pane = panes.first();
+  const container = pane.getByTestId("call-container");
+  await resizeContainer(container, size);
+  await pane.getByTestId("lobby_joinCall").click({ timeout: 60_000 });
+  await expect(pane.locator("[data-layout]")).toBeVisible({ timeout: 60_000 });
+  const component = await callShape(pane);
+  await container.screenshot({
+    path: test.info().outputPath("small-container.png"),
+  });
+  await referenceContext.close();
+
+  // The breakpoints in Element Call's stylesheets are container queries, so a
+  // small container gets the compact footer a small window does, rather than
+  // the full-width one the window's own size would call for
+  expect(component).toEqual(reference);
+  // And that footer is the compact one: a single row of controls, not the
+  // full-height bar with its logo and layout switch that a large window gets
+  expect(component.footerHeight).toBeLessThan(size.height / 3);
+  expect(component.tileHeight + component.footerHeight).toBeLessThanOrEqual(
+    size.height,
+  );
+});
diff --git a/playwright/component/harness.ts b/playwright/component/harness.ts
new file mode 100644
index 000000000..8e1a6e589
--- /dev/null
+++ b/playwright/component/harness.ts
@@ -0,0 +1,126 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, type Locator, type Page } from "@playwright/test";
+
+import { SynapseAdmin } from "../utils/synapse-admin.ts";
+
+/**
+ * Where the component harness is served — `component/dev`, which embeds Element
+ * Call the way a host application would. Not the `baseURL` the rest of the
+ * suite uses: these tests drive a page that contains Element Call rather than
+ * Element Call itself.
+ */
+export const COMPONENT_HARNESS_URL = "https://localhost:3001";
+
+const HOMESERVER_URL = "https://synapse.m.localhost";
+const PASSWORD = "foobarbaz1!";
+
+/**
+ * Registers a user through the Synapse admin API and creates a room for it to
+ * call in, without touching a browser. The harness signs into this account
+ * twice, giving two devices in one page and so a real call between the two
+ * components.
+ */
+export async function createUserAndRoom(
+  name: string,
+): Promise<{ username: string; roomId: string }> {
+  const username = `${name}_${Date.now()}`;
+  const { access_token: accessToken } = await SynapseAdmin.forHomeserver(
+    HOMESERVER_URL,
+  ).registerUser(username, PASSWORD, name);
+
+  const response = await fetch(
+    `${HOMESERVER_URL}/_matrix/client/v3/createRoom`,
+    {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${accessToken}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({ name: `${name}'s call`, preset: "private_chat" }),
+    },
+  );
+  if (!response.ok)
+    throw new Error(
+      `Could not create a room: ${response.status} ${await response.text()}`,
+    );
+  const { room_id: roomId } = (await response.json()) as { room_id: string };
+
+  return { username, roomId };
+}
+
+/**
+ * Opens the harness signed in as the given user, and waits for both embedded
+ * calls to appear.
+ *
+ * @returns The two containers the host gave Element Call, in order.
+ */
+export async function startHarness(
+  page: Page,
+  username: string,
+  roomId: string,
+): Promise<Locator> {
+  const query = new URLSearchParams({
+    homeserver: HOMESERVER_URL,
+    username,
+    password: PASSWORD,
+    room: roomId,
+  });
+  await page.goto(`${COMPONENT_HARNESS_URL}/?${query.toString()}`);
+  await page.getByRole("button", { name: "Start" }).click();
+
+  const panes = page.getByTestId("call-pane");
+  // Two logins, two crypto setups and two initial syncs happen first
+  await expect(panes).toHaveCount(2, { timeout: 120_000 });
+  return panes;
+}
+
+/**
+ * Asserts that one element is drawn entirely inside another.
+ *
+ * This is the check that being a component rather than an iframe costs us: an
+ * iframe could not paint outside itself whatever its stylesheets said, whereas
+ * a component shares the page and has to be made to stay put.
+ */
+export async function expectWithin(
+  inner: Locator,
+  outer: Locator,
+): Promise<void> {
+  await expect(inner).toBeVisible();
+  const innerBox = await inner.boundingBox();
+  const outerBox = await outer.boundingBox();
+  if (innerBox === null || outerBox === null)
+    throw new Error("Expected both elements to be laid out");
+
+  // A pixel of slack, for subpixel layout
+  const slack = 1;
+  expect(innerBox.x).toBeGreaterThanOrEqual(outerBox.x - slack);
+  expect(innerBox.y).toBeGreaterThanOrEqual(outerBox.y - slack);
+  expect(innerBox.x + innerBox.width).toBeLessThanOrEqual(
+    outerBox.x + outerBox.width + slack,
+  );
+  expect(innerBox.y + innerBox.height).toBeLessThanOrEqual(
+    outerBox.y + outerBox.height + slack,
+  );
+}
+
+/**
+ * Gives one of the harness's containers a new size. Element Call lays itself
+ * out for the size of its container, so this is how a test puts it into a
+ * particular mode: a flat or narrow one, a picture-in-picture, or a full-size
+ * window, without the window itself changing at all.
+ */
+export async function resizeContainer(
+  container: Locator,
+  size: { width: number; height: number },
+): Promise<void> {
+  await container.evaluate((element, { width, height }) => {
+    element.style.width = `${width}px`;
+    element.style.height = `${height}px`;
+  }, size);
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 3d35a87ff..bc71e38e6 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -223,6 +223,9 @@ importers:
       postcss-preset-env:
         specifier: ^10.0.0
         version: 10.6.1(postcss@8.5.26)
+      postcss-selector-parser:
+        specifier: ^7.1.1
+        version: 7.1.1
       posthog-js:
         specifier: 1.408.2
         version: 1.408.2
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index c32736caa..9e4f0fd6f 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -1,3 +1,7 @@
+supportedArchitectures:
+  os: [current, linux]
+  cpu: [current, arm64]
+  libc: [current, glibc]
 minimumReleaseAgeExclude:
   - "@vector-im/compound-design-tokens"
   - "@vector-im/compound-web"
diff --git a/scripts/check-component-externals.mjs b/scripts/check-component-externals.mjs
new file mode 100644
index 000000000..ee7d57da0
--- /dev/null
+++ b/scripts/check-component-externals.mjs
@@ -0,0 +1,140 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * Checks that the component build leaves the packages a host must supply to
+ * the host.
+ *
+ * A host application already has React, the Matrix SDK and LiveKit, and a
+ * second copy of any of them is worse than dead weight: React would hold two
+ * sets of hooks, and the Matrix client would run two sync loops. So the
+ * component build lists them as external — but that list has to name every
+ * subpath, since the bundler silently ignores the pattern and callback forms
+ * of the option, and an import it does not cover is bundled with no warning at
+ * all. That is the failure this guards against.
+ *
+ * It reads the list from the build config itself, so there is one copy of it,
+ * and compares it against every import of those packages in the source.
+ *
+ * The comparison is deliberately over-approximate: it looks at all of `src`
+ * rather than only the modules the component actually pulls in, so it will
+ * sometimes ask for a subpath that only the standalone app imports. Listing
+ * one the component never imports costs nothing — the bundler ignores it —
+ * whereas missing one costs a duplicate package.
+ */
+
+import { readdir, readFile } from "node:fs/promises";
+import { join } from "node:path";
+import { loadConfigFromFile } from "vite";
+
+const CONFIG = "vite-component.config.ts";
+const SOURCES = ["src", "component"];
+
+/** The packages whose duplication would break a host, rather than merely enlarge it. */
+const MUST_BE_EXTERNAL = [
+  "react",
+  "react-dom",
+  "matrix-js-sdk",
+  "livekit-client",
+];
+
+const isTestFile = (name) =>
+  name.includes(".test.") || name.includes(".stories.");
+
+/** Every source file under the given directories, recursively. */
+async function* sourceFiles(dir) {
+  for (const entry of await readdir(dir, { withFileTypes: true })) {
+    const path = join(dir, entry.name);
+    if (entry.isDirectory()) yield* sourceFiles(path);
+    else if (/\.(ts|tsx)$/.test(entry.name) && !isTestFile(entry.name))
+      yield path;
+  }
+}
+
+/**
+ * The module specifiers a source file imports. Covers `from "…"` (which is
+ * both static imports and re-exports), bare `import "…"` for side effects, and
+ * dynamic `import("…")`.
+ */
+function imports(source) {
+  const specifiers = [];
+  for (const pattern of [
+    /\bfrom\s*["']([^"']+)["']/g,
+    /\bimport\s*\(\s*["']([^"']+)["']\s*\)/g,
+    /^\s*import\s+["']([^"']+)["']/gm,
+  ])
+    for (const [, specifier] of source.matchAll(pattern))
+      specifiers.push(specifier);
+  return specifiers;
+}
+
+/**
+ * Whether a specifier is an import of one of the packages we care about.
+ *
+ * Imports carrying a resource query — `?worker`, `?inline` and friends — are
+ * not, whatever package they name. Those ask the bundler for a script to run
+ * in a context of its own, which has to be self-contained and shares no state
+ * with the host's copy of anything. Worker sub-builds do not inherit this
+ * option anyway.
+ */
+const mustBeExternal = (specifier) =>
+  !specifier.includes("?") &&
+  MUST_BE_EXTERNAL.some(
+    (pkg) => specifier === pkg || specifier.startsWith(`${pkg}/`),
+  );
+
+const loaded = await loadConfigFromFile(
+  { command: "build", mode: "production" },
+  CONFIG,
+);
+if (loaded === null) {
+  console.error(`Could not load ${CONFIG}`);
+  process.exit(1);
+}
+const declared = new Set(loaded.config.build?.rollupOptions?.external ?? []);
+if (declared.size === 0) {
+  console.error(
+    `${CONFIG} declares nothing external. Either the option moved, or the ` +
+      `list is empty; either way this check is not looking at what it thinks.`,
+  );
+  process.exit(1);
+}
+
+// Where each missing specifier is imported, so the message can point at it
+const missing = new Map();
+const seen = new Set();
+for (const dir of SOURCES)
+  for await (const file of sourceFiles(dir)) {
+    const source = await readFile(file, "utf8");
+    for (const specifier of imports(source)) {
+      if (!mustBeExternal(specifier)) continue;
+      seen.add(specifier);
+      if (declared.has(specifier)) continue;
+      const files = missing.get(specifier) ?? [];
+      files.push(file);
+      missing.set(specifier, files);
+    }
+  }
+
+if (missing.size > 0) {
+  console.error(
+    `${CONFIG} does not declare these imports external, so the component ` +
+      `build would bundle its own copy of them:\n`,
+  );
+  for (const [specifier, files] of [...missing].sort())
+    console.error(`  ${specifier}\n    imported by ${files.join(", ")}`);
+  console.error(`\nAdd each one to the \`external\` list in ${CONFIG}.`);
+  process.exit(1);
+}
+
+// Deliberately no complaint about declarations nothing imports. Some of them
+// cannot be seen from the source at all — `react/jsx-runtime` is injected by
+// the JSX transform — and an extra declaration is inert, so there is nothing
+// to warn about.
+console.log(
+  `${declared.size} external declarations cover all ${seen.size} imports of ${MUST_BE_EXTERNAL.join(", ")}.`,
+);
diff --git a/sdk/main.ts b/sdk/main.ts
index a001af65c..6cd37032d 100644
--- a/sdk/main.ts
+++ b/sdk/main.ts
@@ -46,7 +46,10 @@ import {
 // Can this be done in the tsconfig.json
 import { type TextStreamInfo } from "../node_modules/livekit-client/dist/src/room/types";
 import { type Behavior, constant } from "../src/state/Behavior";
-import { createCallViewModel$ } from "../src/state/CallViewModel/CallViewModel";
+import {
+  callViewModelOptionsFromParams,
+  createCallViewModel$,
+} from "../src/state/CallViewModel/CallViewModel";
 import { ObservableScope } from "../src/state/ObservableScope";
 import { getUrlParams } from "../src/UrlParams";
 import { MuteStates } from "../src/state/MuteStates";
@@ -54,12 +57,10 @@ import { MediaDevices } from "../src/state/MediaDevices";
 import { E2eeType } from "../src/e2ee/e2eeType";
 import { currentAndPrev, TEXT_LK_TOPIC, tryMakeSticky } from "./helper";
 import { logger as rootLogger } from "matrix-js-sdk/lib/logger";
-import {
-  ElementWidgetActions,
-  widget as _widget,
-  initializeWidget,
-} from "../src/widget";
+import { initializeWidget } from "../src/widget";
 import { type Connection } from "../src/state/CallViewModel/remoteMembers/Connection";
+import { createWidgetHostBridge } from "../src/HostBridge";
+import { observeElementSize$ } from "../src/utils/elementSize";
 
 interface MatrixRTCSdk {
   /**
@@ -109,14 +110,15 @@ export async function createMatrixRTCSdk(
   const scope = new ObservableScope();
 
   // widget client
-  initializeWidget(application, true);
-  const widget = _widget;
+  const widget = initializeWidget(application, true);
   if (!widget) throw Error("No widget. This webapp can only start as a widget");
   const client = await widget.client;
+  const hostBridge = createWidgetHostBridge(widget);
   logger.info("client created");
 
   // url params
-  const { roomId } = getUrlParams();
+  const urlParams = getUrlParams();
+  const { roomId, controlledAudioDevices, callIntent } = urlParams;
   if (roomId === null) throw Error("could not get roomId from url params");
   const room = client.getRoom(roomId);
   if (room === null) throw Error("could not get room from client");
@@ -128,11 +130,16 @@ export async function createMatrixRTCSdk(
   const rtcSession = rtcSessionManager.getRoomSession(room);
 
   // media devices
-  const mediaDevices = new MediaDevices(scope);
-  const muteStates = new MuteStates(scope, mediaDevices, {
-    audioEnabled: false,
-    videoEnabled: false,
+  const mediaDevices = new MediaDevices(scope, {
+    controlledAudioDevices,
+    callIntent,
   });
+  const muteStates = new MuteStates(
+    scope,
+    mediaDevices,
+    { audioEnabled: false, videoEnabled: false },
+    hostBridge,
+  );
 
   // call view model
   const callViewModel = createCallViewModel$(
@@ -141,7 +148,13 @@ export async function createMatrixRTCSdk(
     room,
     mediaDevices,
     muteStates,
-    { encryptionSystem: { kind: E2eeType.PER_PARTICIPANT } },
+    {
+      ...callViewModelOptionsFromParams(urlParams),
+      encryptionSystem: { kind: E2eeType.PER_PARTICIPANT },
+      hostBridge,
+      // The SDK owns its page, so the body is the space it has
+      windowSize$: scope.behavior(observeElementSize$(document.body)),
+    },
     of({}),
     of({}),
     constant({ supported: false, processor: undefined }),
@@ -282,18 +295,17 @@ export async function createMatrixRTCSdk(
       });
       await leaveResolver.promise;
       logger.info("send Unstick");
-      await widget.api
+      await hostBridge
         .setAlwaysOnScreen(false)
-        .catch((e) =>
-          logger.error(
-            "Failed to set call widget `alwaysOnScreen` to false",
-            e,
-          ),
+        .catch((e: unknown) =>
+          logger.error("Failed to set `alwaysOnScreen` to false", e),
         );
       logger.info("send Close");
-      await widget.api.transport
-        .send(ElementWidgetActions.Close, {})
-        .catch((e) => logger.error("Failed to send close action", e));
+      await hostBridge
+        .close?.()
+        .catch((e: unknown) =>
+          logger.error("Failed to ask the host to close", e),
+        );
     };
 
     // schedule close first and then leave (scope.end)
diff --git a/src/App.tsx b/src/App.tsx
index 8f6ef21a1..c07553afc 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -9,14 +9,22 @@ import {
   type FC,
   type JSX,
   Suspense,
+  useCallback,
   useEffect,
-  useMemo,
   useState,
 } from "react";
-import { BrowserRouter, Route, useLocation, Routes } from "react-router-dom";
+import {
+  BrowserRouter,
+  Route,
+  useLocation,
+  useNavigate,
+  Routes,
+} from "react-router-dom";
 import * as Sentry from "@sentry/react";
 import { TooltipProvider } from "@vector-im/compound-web";
 import { logger } from "matrix-js-sdk/lib/logger";
+import { type MatrixClient } from "matrix-js-sdk";
+import { I18nextProvider } from "react-i18next";
 
 import { HomePage } from "./home/HomePage";
 import { LoginPage } from "./auth/LoginPage";
@@ -25,13 +33,27 @@ import { RoomPage } from "./room/RoomPage";
 import { ClientProvider } from "./ClientContext";
 import { ErrorPage, LoadingPage } from "./FullScreenView";
 import { Initializer } from "./initializer";
-import { widget } from "./widget";
+import { type WidgetHelpers } from "./widget";
 import { useTheme } from "./useTheme";
 import { ProcessorProvider } from "./livekit/TrackProcessorContext";
 import { type AppViewModel } from "./state/AppViewModel";
 import { MediaDevicesContext } from "./MediaDevicesContext";
-import { getUrlParams, HeaderStyle, useUrlParams } from "./UrlParams";
+import {
+  HeaderStyle,
+  UrlParamsProvider,
+  useUrlParams,
+  useUrlParamsFromLocation,
+} from "./UrlParams";
 import { AppBar } from "./AppBar";
+import { i18n } from "./utils/i18n";
+import { useRootElement } from "./RootElementContext";
+import {
+  createWidgetHostBridge,
+  HostBridgeProvider,
+  nullHostBridge,
+} from "./HostBridge";
+import { useInitial } from "./useInitial";
+import { LeaveToHomeProvider } from "./LeaveToHomeContext";
 
 const SentryRoute = Sentry.withSentryReactRouterV7Routing(Route);
 
@@ -39,15 +61,38 @@ interface SimpleProviderProps {
   children: JSX.Element;
 }
 
+/**
+ * Supplies the URL-derived params to the rest of the app. Only the standalone
+ * and widget builds own the URL, so this lives here in the app shell rather
+ * than alongside the context itself.
+ */
+const LocationUrlParamsProvider: FC<SimpleProviderProps> = ({ children }) => {
+  const urlParams = useUrlParamsFromLocation();
+  return <UrlParamsProvider value={urlParams}>{children}</UrlParamsProvider>;
+};
+
+/**
+ * Supplies the way home. Only the app has one — its home page, with the list
+ * of recent calls — so this, too, lives in the app shell.
+ */
+const HomeProvider: FC<SimpleProviderProps> = ({ children }) => {
+  const navigate = useNavigate();
+  const leaveToHome = useCallback(() => {
+    navigate("/")?.catch((e) => logger.error("Failed to navigate home", e));
+  }, [navigate]);
+  return (
+    <LeaveToHomeProvider value={leaveToHome}>{children}</LeaveToHomeProvider>
+  );
+};
+
 const BackgroundProvider: FC<SimpleProviderProps> = ({ children }) => {
   const { pathname } = useLocation();
   const { background } = useUrlParams();
+  const rootElement = useRootElement();
 
   useEffect(() => {
-    document
-      .getElementsByTagName("body")[0]
-      .setAttribute("data-background", background);
-  }, [pathname, background]);
+    rootElement.setAttribute("data-background", background);
+  }, [pathname, background, rootElement]);
 
   return children;
 };
@@ -57,61 +102,89 @@ const ThemeProvider: FC<SimpleProviderProps> = ({ children }) => {
   return children;
 };
 
+/** Wraps the app in an {@link AppBar}, if the params ask for one. */
+const MaybeAppBar: FC<SimpleProviderProps> = ({ children }) => {
+  const { header } = useUrlParams();
+  return header === HeaderStyle.AppBar ? <AppBar>{children}</AppBar> : children;
+};
+
 interface Props {
   vm: AppViewModel;
+  /** A point of access to the widget API, if running as a widget. */
+  widget: WidgetHelpers | null;
 }
 
-export const App: FC<Props> = ({ vm }) => {
+export const App: FC<Props> = ({ vm, widget }) => {
+  // The standalone build has no host; the widget build's host is the client it
+  // is a widget of.
+  const hostBridge = useInitial(() =>
+    widget === null ? nullHostBridge : createWidgetHostBridge(widget),
+  );
   const [loaded, setLoaded] = useState(false);
   useEffect(() => {
     Initializer.init()
       ?.then(async () => {
         if (loaded) return;
         setLoaded(true);
-        await widget?.api.sendContentLoaded();
+        await hostBridge.contentLoaded();
       })
       .catch(logger.error);
   });
 
-  // Since we are outside the router component, we cannot use useUrlParams here
-  const { header } = useMemo(getUrlParams, []);
-
-  const content = loaded ? (
-    <ClientProvider>
-      <MediaDevicesContext value={vm.mediaDevices}>
-        <ProcessorProvider>
-          <Sentry.ErrorBoundary
-            fallback={(error) => <ErrorPage error={error} widget={widget} />}
-          >
-            <Routes>
-              <SentryRoute path="/" element={<HomePage />} />
-              <SentryRoute path="/login" element={<LoginPage />} />
-              <SentryRoute path="/register" element={<RegisterPage />} />
-              <SentryRoute path="*" element={<RoomPage />} />
-            </Routes>
-          </Sentry.ErrorBoundary>
-        </ProcessorProvider>
-      </MediaDevicesContext>
-    </ClientProvider>
-  ) : (
-    <LoadingPage />
+  // As a widget, the client comes from the host over the widget API. Standalone,
+  // Element Call finds one itself, so there is nothing to wait for here.
+  const [widgetClient, setWidgetClient] = useState<MatrixClient | undefined>(
+    undefined,
   );
+  useEffect(() => {
+    if (widget === null) return;
+    widget.client
+      .then(setWidgetClient)
+      .catch((e) => logger.error("Failed to obtain the host's client", e));
+  }, [widget]);
+  const clientReady = widget === null || widgetClient !== undefined;
+
+  const content =
+    loaded && clientReady ? (
+      <ClientProvider client={widgetClient}>
+        <MediaDevicesContext value={vm.mediaDevices}>
+          <ProcessorProvider>
+            <Sentry.ErrorBoundary
+              fallback={(error) => <ErrorPage error={error} />}
+            >
+              <Routes>
+                <SentryRoute path="/" element={<HomePage />} />
+                <SentryRoute path="/login" element={<LoginPage />} />
+                <SentryRoute path="/register" element={<RegisterPage />} />
+                <SentryRoute path="*" element={<RoomPage />} />
+              </Routes>
+            </Sentry.ErrorBoundary>
+          </ProcessorProvider>
+        </MediaDevicesContext>
+      </ClientProvider>
+    ) : (
+      <LoadingPage />
+    );
 
   return (
-    <BrowserRouter>
-      <BackgroundProvider>
-        <ThemeProvider>
-          <TooltipProvider>
-            <Suspense fallback={null}>
-              {header === HeaderStyle.AppBar ? (
-                <AppBar>{content}</AppBar>
-              ) : (
-                content
-              )}
-            </Suspense>
-          </TooltipProvider>
-        </ThemeProvider>
-      </BackgroundProvider>
-    </BrowserRouter>
+    <I18nextProvider i18n={i18n}>
+      <HostBridgeProvider value={hostBridge}>
+        <BrowserRouter>
+          <LocationUrlParamsProvider>
+            <HomeProvider>
+              <BackgroundProvider>
+                <ThemeProvider>
+                  <TooltipProvider>
+                    <Suspense fallback={null}>
+                      <MaybeAppBar>{content}</MaybeAppBar>
+                    </Suspense>
+                  </TooltipProvider>
+                </ThemeProvider>
+              </BackgroundProvider>
+            </HomeProvider>
+          </LocationUrlParamsProvider>
+        </BrowserRouter>
+      </HostBridgeProvider>
+    </I18nextProvider>
   );
 };
diff --git a/src/AppBar.module.css b/src/AppBar.module.css
index cc63854e7..1b234a223 100644
--- a/src/AppBar.module.css
+++ b/src/AppBar.module.css
@@ -68,7 +68,7 @@
 }
 
 /* Hide everything but the subtitle in small windows */
-@media (max-height: 450px) {
+@container element-call (max-height: 450px) {
   .bar {
     display: none;
   }
@@ -131,7 +131,7 @@
   }
 }
 
-body[data-platform="ios"] {
+[data-element-call-root][data-platform="ios"] {
   .bar > header {
     grid-template-rows: minmax(var(--cpd-space-11x), auto) var(--cpd-space-4x);
     grid-template-areas: "primaryButton title secondaryButton";
@@ -166,7 +166,7 @@ body[data-platform="ios"] {
   }
 
   /* Hide everything but the subtitle in small windows */
-  @media (max-height: 450px) {
+  @container element-call (max-height: 450px) {
     .bar:has(.subtitle) > header {
       grid-template-rows: var(--cpd-space-4x) minmax(var(--cpd-space-5x), auto);
       grid-template-areas: "." "subtitle";
diff --git a/src/Avatar.test.tsx b/src/Avatar.test.tsx
index 1e32de0e0..c5d5e25af 100644
--- a/src/Avatar.test.tsx
+++ b/src/Avatar.test.tsx
@@ -9,18 +9,22 @@ import { afterEach, expect, test, vi } from "vitest";
 import { render, screen } from "@testing-library/react";
 import { type MatrixClient } from "matrix-js-sdk";
 import { type FC, type PropsWithChildren } from "react";
-import { type WidgetApi } from "matrix-widget-api";
 
 import { ClientContextProvider } from "./ClientContext";
-import { Avatar, getAvatarFromWidgetAPI } from "./Avatar";
+import { Avatar } from "./Avatar";
 import { mockMatrixRoomMember, mockRtcMembership } from "./utils/test";
-import { widget } from "./widget";
+import {
+  type HostBridge,
+  HostBridgeProvider,
+  nullHostBridge,
+} from "./HostBridge";
 
 const TestComponent: FC<
   PropsWithChildren<{
     client: MatrixClient;
+    hostBridge?: HostBridge;
   }>
-> = ({ client, children }) => {
+> = ({ client, hostBridge = nullHostBridge, children }) => {
   return (
     <ClientContextProvider
       value={{
@@ -38,17 +42,11 @@ const TestComponent: FC<
         },
       }}
     >
-      {children}
+      <HostBridgeProvider value={hostBridge}>{children}</HostBridgeProvider>
     </ClientContextProvider>
   );
 };
 
-vi.mock("./widget", () => ({
-  widget: {
-    api: null, // Ideally we'd only mock this in the as a widget test so the whole module is otherwise null, but just nulling `api` by default works well enough
-  },
-}));
-
 afterEach(() => {
   vi.unstubAllGlobals();
 });
@@ -135,7 +133,7 @@ test("should attempt to fetch authenticated media from the server", async () =>
   });
 });
 
-test("should attempt to use widget API if running as a widget", async () => {
+test("should download media through the host when it offers to", async () => {
   const expectedMXCUrl = "mxc://example.org/alice-avatar";
   const expectedObjectURL = "my-object-url";
   const theBlob = new Blob([]);
@@ -151,8 +149,8 @@ test("should attempt to use widget API if running as a widget", async () => {
     getAccessToken: () => undefined,
   } as unknown as MatrixClient);
 
-  widget!.api = { downloadFile: vi.fn() } as unknown as WidgetApi;
-  vi.spyOn(widget!.api, "downloadFile").mockResolvedValue({ file: theBlob });
+  const downloadMedia = vi.fn().mockResolvedValue(theBlob);
+  const hostBridge: HostBridge = { ...nullHostBridge, downloadMedia };
   const member = mockMatrixRoomMember(
     mockRtcMembership("@alice:example.org", "AAAA"),
     {
@@ -161,7 +159,7 @@ test("should attempt to use widget API if running as a widget", async () => {
   );
   const displayName = "Alice";
   render(
-    <TestComponent client={client}>
+    <TestComponent client={client} hostBridge={hostBridge}>
       <Avatar
         id={member.userId}
         name={displayName}
@@ -176,38 +174,5 @@ test("should attempt to use widget API if running as a widget", async () => {
     document.querySelector(`img[src='${expectedObjectURL}']`),
   );
 
-  expect(widget!.api.downloadFile).toBeCalledWith(expectedMXCUrl);
-});
-
-test("Supports download files as base64", async () => {
-  const expectedMXCUrl = "mxc://example.org/alice-avatar";
-  const expectedBase64 =
-    "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAIAAACQkWg2AAADIElEQVR4nAAQA+/8ApxhEfFNuwna" +
-    "+DO1pFMx5YDg6gb8p1WFkbFSox9H6r5c8jp1gxlHXrDfA/oQFi4A0gTXH9YBNgwRm12xO68QP6lv" +
-    "ZLKH9qW1VM6kz6zA3T1Ui8J+Xbnh2BZ7oXDe/2gajzoA6j1JGotpz99xO+T2NR634Nhx3zhuera/" +
-    "UdrpMLdEpwWXLnSqZRasGsrl93FjdTwRBMaqsx6vJksnPOmV9ttbXFIOb0XDGPbVythSC2n7P/bS" +
-    "Zv0U0QqbBLk/5Wu1werYzAHiz11Bj8bEylQ92Pxvo+PwF6/KbGnIHTvGZkFzDkMnqz3g7Pw3NOSP" +
-    "oV+qfyJuSI0AeZmrPejFQ8kzBSDWO8D7lr4+6ePRBRmZtKCf+fNjSCOyb5jqwhBnD2cycbJtQQbR" +
-    "A4qdPG2ONfTPeQgi96+zT7grBI0JwvgFBceJdLJd4BX1VQIyY+j7OYueNWqEpf8iYgMj78I95eRt" +
-    "nfPLwlxhVns84iL4Yvw8jDrB9vQi8ktpsdJOMiDwKrBGD3q56COD2oIA96CCBgiro4tkvkumZSAc" +
-    "ZKXRLsziUFGytWJLaPjwnzXv2hicPy6k9AXsF3QkysOZAkB3m9XPpixhq9b0OKqV/zZx3L79o6wZ" +
-    "Dr40J7sj7f+ARd545CP01r5omHt94tbnjgA46HsM2OhP+qQ882LN+Bhscq2WSHGSHT4J9MQcsWZP" +
-    "2+N2LdPy61MN4/1++BJHmDcDLQBUEwLvjZp1fRfzxV7yirwIiOA7Vr8z+1yvS/pSkfUzkjswybOd" +
-    "M5i0I8Q69MTXAKxqtR0/tyGkfCmHfupGASp/SAT9J8f3aQV+gDbpva592v4w8Cv5EMm7CzZPwThF" +
-    "kgTChNPts7F03ccxpblfIz0EiAON1DKk71rX07BvDlLHY1ItPuqZ7hjy19jrAgl+QqEE1btHVA5R" +
-    "uAnRXpEWc6rjARlJY5G1wbMk12rrqpr8rhR3YpFgLgOx4BtQ0D/hGe7KANSGBMQojmObId0asCmd" +
-    "XzmnQI9P8QnwsO9vtqZlgIoU4g+f2/G8Q3/nVMX7dujniwEAAP//KmiQs7P8MeIAAAAASUVORK5C" +
-    "YII=";
-  const mockWidgetAPI = {
-    downloadFile: vi.fn().mockImplementation(async (contentUri) => {
-      if (contentUri !== expectedMXCUrl) {
-        return Promise.reject(new Error("Unexpected content URI"));
-      }
-      return { file: expectedBase64 };
-    }),
-  } as unknown as WidgetApi;
-
-  const blob = await getAvatarFromWidgetAPI(mockWidgetAPI, expectedMXCUrl);
-
-  expect(blob).toBeInstanceOf(Blob);
+  expect(downloadMedia).toBeCalledWith(expectedMXCUrl);
 });
diff --git a/src/Avatar.tsx b/src/Avatar.tsx
index 99940540d..185ae97b4 100644
--- a/src/Avatar.tsx
+++ b/src/Avatar.tsx
@@ -14,10 +14,9 @@ import {
 } from "react";
 import { Avatar as CompoundAvatar } from "@vector-im/compound-web";
 import { type MatrixClient } from "matrix-js-sdk";
-import { type WidgetApi } from "matrix-widget-api";
 
 import { useClientState } from "./ClientContext";
-import { widget } from "./widget";
+import { useHostBridge } from "./HostBridge";
 
 export enum Size {
   XS = "xs",
@@ -76,6 +75,7 @@ export const Avatar: FC<Props> = ({
   ...props
 }) => {
   const clientState = useClientState();
+  const hostBridge = useHostBridge();
 
   const sizePx = useMemo(
     () =>
@@ -87,7 +87,8 @@ export const Avatar: FC<Props> = ({
 
   const [avatarUrl, setAvatarUrl] = useState<string | undefined>(undefined);
 
-  // In theory, a change in `clientState` or `sizePx` could run extra getAvatarFromWidgetAPI calls, but in practice they should be stable long before this code runs.
+  // In theory, a change in `clientState` or `sizePx` could run extra media
+  // downloads, but in practice they should be stable long before this code runs.
   useEffect(() => {
     if (!src) {
       setAvatarUrl(undefined);
@@ -96,8 +97,8 @@ export const Avatar: FC<Props> = ({
 
     let blob: Promise<Blob>;
 
-    if (widget?.api) {
-      blob = getAvatarFromWidgetAPI(widget.api, src);
+    if (hostBridge.downloadMedia) {
+      blob = hostBridge.downloadMedia(src);
     } else if (
       clientState?.state === "valid" &&
       clientState.authenticated?.client &&
@@ -132,7 +133,7 @@ export const Avatar: FC<Props> = ({
         URL.revokeObjectURL(objectUrl);
       }
     };
-  }, [clientState, src, sizePx]);
+  }, [clientState, hostBridge, src, sizePx]);
 
   return (
     <CompoundAvatar
@@ -172,24 +173,3 @@ async function getAvatarFromServer(
 
   return blob;
 }
-
-// export for testing
-export async function getAvatarFromWidgetAPI(
-  api: WidgetApi,
-  src: string,
-): Promise<Blob> {
-  const response = await api.downloadFile(src);
-  const file = response.file;
-
-  // element-web sends a Blob, and the MSC4039 is considering changing the spec to strictly Blob, so only handling that
-  if (file instanceof Blob) {
-    return file;
-  } else if (typeof file === "string") {
-    // it is a base64 string
-    const bytes = Uint8Array.from(atob(file), (c) => c.charCodeAt(0));
-    return new Blob([bytes]);
-  }
-  throw new Error(
-    "Downloaded file format is not supported: " + typeof file + "",
-  );
-}
diff --git a/src/ClientContext.test.tsx b/src/ClientContext.test.tsx
new file mode 100644
index 000000000..65ff03d03
--- /dev/null
+++ b/src/ClientContext.test.tsx
@@ -0,0 +1,115 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, test, vi } from "vitest";
+import { render, waitFor } from "@testing-library/react";
+import { BrowserRouter } from "react-router-dom";
+import { type MatrixClient } from "matrix-js-sdk";
+import { type FC } from "react";
+
+import { ClientProvider, useClientState } from "./ClientContext";
+
+const mockClient = (userId = "@alice:example.org"): MatrixClient =>
+  ({
+    on: vi.fn(),
+    removeListener: vi.fn(),
+    getUserId: () => userId,
+    getDeviceId: () => "AAAA",
+    stopClient: vi.fn(),
+  }) as Partial<MatrixClient> as MatrixClient;
+
+/** Reports what the context says, so a test can assert on it. */
+const ShowClientState: FC = () => {
+  const state = useClientState();
+  if (state === undefined) return <span>loading</span>;
+  if (state.state === "error") return <span>error</span>;
+  return (
+    <span>{state.authenticated?.client.getUserId() ?? "unauthenticated"}</span>
+  );
+};
+
+test("uses a client supplied by the host without waiting", () => {
+  const client = mockClient();
+
+  const { container } = render(
+    <BrowserRouter>
+      <ClientProvider client={client}>
+        <ShowClientState />
+      </ClientProvider>
+    </BrowserRouter>,
+  );
+
+  // Available on the very first render: a supplied client needs no session
+  // restoring, so there is no loading state to pass through.
+  expect(container.textContent).toBe("@alice:example.org");
+});
+
+test("does not claim exclusive use of storage when given a client", () => {
+  // The channel is created when the module loads, so spy on the prototype
+  // rather than trying to replace the global.
+  const postMessage = vi.spyOn(BroadcastChannel.prototype, "postMessage");
+
+  render(
+    <BrowserRouter>
+      <ClientProvider client={mockClient()}>
+        <ShowClientState />
+      </ClientProvider>
+    </BrowserRouter>,
+  );
+
+  // The broadcast shuts down other instances to protect Element Call's own
+  // stores. A host's client brings its own, so there is nothing to protect.
+  expect(postMessage).not.toHaveBeenCalled();
+
+  postMessage.mockRestore();
+});
+
+test("follows the client when the host swaps it", () => {
+  const first = mockClient();
+  const second = mockClient("@bob:example.org");
+
+  const { container, rerender } = render(
+    <BrowserRouter>
+      <ClientProvider client={first}>
+        <ShowClientState />
+      </ClientProvider>
+    </BrowserRouter>,
+  );
+  expect(container.textContent).toBe("@alice:example.org");
+
+  // A host that re-authenticates hands us a new client on a mounted component
+  rerender(
+    <BrowserRouter>
+      <ClientProvider client={second}>
+        <ShowClientState />
+      </ClientProvider>
+    </BrowserRouter>,
+  );
+
+  expect(container.textContent).toBe("@bob:example.org");
+});
+
+test("finds a client of its own when the host supplies none", async () => {
+  const client = mockClient();
+  vi.doMock("./utils/spa", () => ({
+    initSPA: vi.fn().mockResolvedValue({ client, passwordlessUser: true }),
+  }));
+
+  const { container } = render(
+    <BrowserRouter>
+      <ClientProvider>
+        <ShowClientState />
+      </ClientProvider>
+    </BrowserRouter>,
+  );
+
+  // Nothing to show until a session has been restored or created
+  expect(container.textContent).toBe("loading");
+  await waitFor(() => expect(container.textContent).toBe("@alice:example.org"));
+
+  vi.doUnmock("./utils/spa");
+});
diff --git a/src/ClientContext.tsx b/src/ClientContext.tsx
index f2ff3dd4b..526581996 100644
--- a/src/ClientContext.tsx
+++ b/src/ClientContext.tsx
@@ -16,14 +16,13 @@ import {
   useMemo,
   type JSX,
 } from "react";
-import { useNavigate } from "react-router-dom";
 import { logger } from "matrix-js-sdk/lib/logger";
 import { type ISyncStateData, type SyncState } from "matrix-js-sdk/lib/sync";
 import { ClientEvent, type MatrixClient } from "matrix-js-sdk";
 
-import type { WidgetApi } from "matrix-widget-api";
 import { ErrorPage } from "./FullScreenView";
-import { widget } from "./widget";
+import { useHostBridge } from "./HostBridge";
+import { useLeaveToHome } from "./LeaveToHomeContext";
 import {
   PosthogAnalytics,
   RegistrationType,
@@ -134,18 +133,48 @@ const loadChannel =
 
 interface Props {
   children: JSX.Element;
+  /**
+   * The client Element Call should use.
+   *
+   * An application hosting Element Call as a component already has a client,
+   * and owns the user's session; supplying it here means Element Call neither
+   * authenticates anyone nor manages their session. Left out, Element Call finds a client
+   * itself — from the widget API, or by restoring or creating a session of its
+   * own.
+   */
+  client?: MatrixClient;
 }
 
-export const ClientProvider: FC<Props> = ({ children }) => {
-  const navigate = useNavigate();
+export const ClientProvider: FC<Props> = ({ children, client }) => {
+  const leaveToHome = useLeaveToHome();
+  const hostBridge = useHostBridge();
 
   // null = signed out, undefined = loading
   const [initClientState, setInitClientState] = useState<
     InitResult | null | undefined
-  >(undefined);
+  >(
+    client === undefined
+      ? undefined
+      : // A supplied client belongs to the host, so there is no session of ours
+        // to restore and nothing to wait for.
+        { client, passwordlessUser: false },
+  );
 
   const initializing = useRef(false);
   useEffect(() => {
+    if (client !== undefined) {
+      // Nothing to load, but a host may hand us a different client later — on
+      // re-authenticating, say — so follow whichever one it has given us.
+      setInitClientState((current) =>
+        current?.client === client
+          ? current
+          : { client, passwordlessUser: false },
+      );
+      // Analytics still need to follow the user's choices.
+      if (PosthogAnalytics.instance.isEnabled())
+        PosthogAnalytics.instance.startListeningToSettingsChanges();
+      return;
+    }
     // In case the component is mounted, unmounted, and remounted quickly (as
     // React does in strict mode), we need to make sure not to doubly initialize
     // the client.
@@ -160,7 +189,7 @@ export const ClientProvider: FC<Props> = ({ children }) => {
       })
       .catch((err) => logger.error(err))
       .finally(() => (initializing.current = false));
-  }, []);
+  }, [client]);
 
   const changePassword = useCallback(
     async (password: string) => {
@@ -201,7 +230,6 @@ export const ClientProvider: FC<Props> = ({ children }) => {
 
       saveSession(session);
       setInitClientState({
-        widgetApi: null,
         client,
         passwordlessUser: session.passwordlessUser,
       });
@@ -221,18 +249,20 @@ export const ClientProvider: FC<Props> = ({ children }) => {
     await client.clearStores();
     clearSession();
     setInitClientState(null);
-    await navigate("/");
+    leaveToHome?.();
     PosthogAnalytics.instance.logout();
     PosthogAnalytics.instance.setRegistrationType(RegistrationType.Guest);
-  }, [navigate, initClientState?.client]);
+  }, [leaveToHome, initClientState?.client]);
 
   // To protect against multiple sessions writing to the same storage
   // simultaneously, we send a broadcast message that shuts down all other
-  // running instances of the app. This isn't necessary if the app is running in
-  // a widget though, since then it'll be mostly stateless.
+  // running instances of the app. Element Call only has storage of its own to
+  // protect when it created the session itself; given a client — by a host, or
+  // over the widget API — it is mostly stateless.
+  const ownsSession = client === undefined;
   useEffect(() => {
-    if (!widget) loadChannel?.postMessage({});
-  }, []);
+    if (ownsSession) loadChannel?.postMessage({});
+  }, [ownsSession]);
 
   const [alreadyOpenedErr, setAlreadyOpenedErr] = useState<Error | undefined>(
     undefined,
@@ -307,64 +337,36 @@ export const ClientProvider: FC<Props> = ({ children }) => {
       initClientState.client.on(ClientEvent.Sync, onSync);
     }
 
-    if (initClientState.widgetApi) {
-      const reactSend = initClientState.widgetApi.hasCapability(
-        "org.matrix.msc2762.send.event:m.reaction",
-      );
-      const redactSend = initClientState.widgetApi.hasCapability(
-        "org.matrix.msc2762.send.event:m.room.redaction",
-      );
-      const reactRcv = initClientState.widgetApi.hasCapability(
-        "org.matrix.msc2762.receive.event:m.reaction",
-      );
-      const redactRcv = initClientState.widgetApi.hasCapability(
-        "org.matrix.msc2762.receive.event:m.room.redaction",
-      );
-
-      if (!reactSend || !reactRcv || !redactSend || !redactRcv) {
-        logger.warn("Widget does not support reactions");
-        setSupportsReactions(false);
-      } else {
-        setSupportsReactions(true);
-      }
-    } else {
-      setSupportsReactions(true);
-    }
+    if (!hostBridge.supportsReactions)
+      logger.warn("The host does not permit reactions");
+    setSupportsReactions(hostBridge.supportsReactions);
 
     return (): void => {
       if (initClientState.client) {
         initClientState.client.removeListener(ClientEvent.Sync, onSync);
       }
     };
-  }, [initClientState, onSync]);
+  }, [initClientState, onSync, hostBridge]);
 
   if (alreadyOpenedErr) {
-    return <ErrorPage widget={widget} error={alreadyOpenedErr} />;
+    return <ErrorPage error={alreadyOpenedErr} />;
   }
 
   return <ClientContext value={state}>{children}</ClientContext>;
 };
 
 export type InitResult = {
-  widgetApi: WidgetApi | null;
   client: MatrixClient;
   passwordlessUser: boolean;
 };
 
+/**
+ * Restores or creates a session of Element Call's own. Only reached when no
+ * client was supplied for it to use.
+ */
 async function loadClient(): Promise<InitResult | null> {
-  if (widget) {
-    // We're inside a widget, so let's engage *matryoshka mode*
-    logger.log("Using a matryoshka client");
-    const client = await widget.client;
-    return {
-      widgetApi: widget.api,
-      client,
-      passwordlessUser: false,
-    };
-  } else {
-    const { initSPA } = await import("./utils/spa");
-    return initSPA(loadSession, clearSession);
-  }
+  const { initSPA } = await import("./utils/spa");
+  return initSPA(loadSession, clearSession);
 }
 
 export interface Session {
diff --git a/src/ErrorView.tsx b/src/ErrorView.tsx
index 1309ae046..00ffba372 100644
--- a/src/ErrorView.tsx
+++ b/src/ErrorView.tsx
@@ -20,8 +20,8 @@ import { logger } from "matrix-js-sdk/lib/logger";
 import { RageshakeButton } from "./settings/RageshakeButton";
 import styles from "./ErrorView.module.css";
 import { useUrlParams } from "./UrlParams";
-import { LinkButton } from "./button";
-import { ElementWidgetActions, type WidgetHelpers } from "./widget.ts";
+import { useLeaveToHome } from "./LeaveToHomeContext";
+import { useHostBridge } from "./HostBridge.ts";
 
 interface Props {
   Icon: ComponentType<SVGAttributes<SVGElement>>;
@@ -38,7 +38,6 @@ interface Props {
    */
   fatal?: boolean;
   children: ReactNode;
-  widget: WidgetHelpers | null;
 }
 
 export const ErrorView: FC<Props> = ({
@@ -47,53 +46,47 @@ export const ErrorView: FC<Props> = ({
   rageshake,
   fatal,
   children,
-  widget,
 }) => {
   const { t } = useTranslation();
   const { confineToRoom } = useUrlParams();
+  const hostBridge = useHostBridge();
+  const leaveToHome = useLeaveToHome();
 
   const onReload = useCallback(() => {
     window.location.href = "/";
   }, []);
 
-  const CloseWidgetButton: FC<{ widget: WidgetHelpers }> = ({
-    widget,
+  const CloseButton: FC<{ close: () => Promise<void> }> = ({
+    close,
   }): ReactElement => {
-    // in widget mode we don't want to show the return home button but a close button
-    const closeWidget = (): void => {
-      widget.api.transport
-        .send(ElementWidgetActions.Close, {})
-        .catch((e) => {
-          // What to do here?
-          logger.error("Failed to send close action", e);
-        })
-        .finally(() => {
-          widget.api.transport.stop();
-        });
+    // When the host can dismiss us, offer that instead of a link home
+    const onClose = (): void => {
+      close().catch((e) => {
+        // What to do here?
+        logger.error("Failed to ask the host to close Element Call", e);
+      });
     };
     return (
-      <Button kind="primary" onClick={closeWidget}>
+      <Button kind="primary" onClick={onClose}>
         {t("action.close")}
       </Button>
     );
   };
 
   // Whether the error is considered fatal or pathname is `/` then reload the all app.
-  // If not then navigate to home page.
-  const ReturnToHomeButton = (): ReactElement => {
-    if (fatal || location.pathname === "/") {
-      return (
-        <Button kind="tertiary" className={styles.homeLink} onClick={onReload}>
-          {t("return_home_button")}
-        </Button>
-      );
-    } else {
-      return (
-        <LinkButton kind="tertiary" className={styles.homeLink} to="/">
-          {t("return_home_button")}
-        </LinkButton>
-      );
-    }
+  // If not then navigate to home page. Neither applies when there is no home
+  // to go to.
+  const ReturnToHomeButton = (): ReactElement | null => {
+    if (leaveToHome === null) return null;
+    return (
+      <Button
+        kind="tertiary"
+        className={styles.homeLink}
+        onClick={fatal || location.pathname === "/" ? onReload : leaveToHome}
+      >
+        {t("return_home_button")}
+      </Button>
+    );
   };
 
   return (
@@ -108,8 +101,8 @@ export const ErrorView: FC<Props> = ({
       {rageshake && (
         <RageshakeButton description={`***Error View***: ${title}`} />
       )}
-      {widget ? (
-        <CloseWidgetButton widget={widget} />
+      {hostBridge.close ? (
+        <CloseButton close={hostBridge.close} />
       ) : (
         !confineToRoom && <ReturnToHomeButton />
       )}
diff --git a/src/FullScreenView.tsx b/src/FullScreenView.tsx
index eb84010e5..ea2a4a0d2 100644
--- a/src/FullScreenView.tsx
+++ b/src/FullScreenView.tsx
@@ -17,7 +17,6 @@ import styles from "./FullScreenView.module.css";
 import { useUrlParams } from "./UrlParams";
 import { RichError } from "./RichError";
 import { ErrorView } from "./ErrorView";
-import { type WidgetHelpers } from "./widget.ts";
 
 interface FullScreenViewProps {
   className?: string;
@@ -48,12 +47,11 @@ export const FullScreenView: FC<FullScreenViewProps> = ({
 
 interface ErrorPageProps {
   error: unknown;
-  widget: WidgetHelpers | null;
 }
 
 // Due to this component being used as the crash fallback for Sentry, which has
 // weird type requirements, we can't just give this a type of FC<ErrorPageProps>
-export const ErrorPage = ({ error, widget }: ErrorPageProps): ReactElement => {
+export const ErrorPage = ({ error }: ErrorPageProps): ReactElement => {
   const { t } = useTranslation();
   useEffect(() => {
     logger.error(error);
@@ -66,7 +64,6 @@ export const ErrorPage = ({ error, widget }: ErrorPageProps): ReactElement => {
         error.richMessage
       ) : (
         <ErrorView
-          widget={widget}
           Icon={ErrorSolidIcon}
           title={t("error.generic")}
           rageshake
diff --git a/src/Header.module.css b/src/Header.module.css
index f82f5fbd6..58a710a79 100644
--- a/src/Header.module.css
+++ b/src/Header.module.css
@@ -30,6 +30,11 @@ Please see LICENSE in the repository root for full details.
   display: none;
   align-items: center;
   text-decoration: none;
+  /* A button when it leads home, so undo the browser's button styling */
+  background: none;
+  border: none;
+  padding: 0;
+  cursor: pointer;
 }
 
 .leftNav.hideMobile {
@@ -107,7 +112,7 @@ Please see LICENSE in the repository root for full details.
   gap: var(--cpd-space-1-5x);
 }
 
-@media (min-width: 800px) {
+@container element-call (min-width: 800px) {
   .headerLogo,
   .leftNav.hideMobile,
   .rightNav.hideMobile {
diff --git a/src/Header.tsx b/src/Header.tsx
index cffc34023..e3bda1659 100644
--- a/src/Header.tsx
+++ b/src/Header.tsx
@@ -6,8 +6,13 @@ Please see LICENSE in the repository root for full details.
 */
 
 import classNames from "classnames";
-import { type Ref, type FC, type HTMLAttributes, type ReactNode } from "react";
-import { Link } from "react-router-dom";
+import {
+  type Ref,
+  type FC,
+  type HTMLAttributes,
+  type ReactNode,
+  useCallback,
+} from "react";
 import { useTranslation } from "react-i18next";
 import { Heading, Text } from "@vector-im/compound-web";
 import { UserProfileIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
@@ -16,7 +21,8 @@ import styles from "./Header.module.css";
 import Logo from "./icons/Logo.svg?react";
 import { Avatar, Size } from "./Avatar";
 import { EncryptionLock } from "./room/EncryptionLock";
-import { useMediaQuery } from "./useMediaQuery";
+import { useRootSizeMatches } from "./useRootSize";
+import { useLeaveToHome } from "./LeaveToHomeContext";
 import { DisconnectedBanner } from "./DisconnectedBanner";
 
 interface HeaderProps extends HTMLAttributes<HTMLElement> {
@@ -112,17 +118,30 @@ interface HeaderLogoProps {
   className?: string;
 }
 
+/**
+ * The logo, which is also the way home — when there is a home to go to. As a
+ * component there is not, and it is just the logo.
+ */
 export const HeaderLogo: FC<HeaderLogoProps> = ({ className }) => {
   const { t } = useTranslation();
+  const leaveToHome = useLeaveToHome();
+  const onClick = useCallback(() => leaveToHome?.(), [leaveToHome]);
 
+  if (leaveToHome === null)
+    return (
+      <div className={classNames(styles.headerLogo, className)}>
+        <Logo />
+      </div>
+    );
   return (
-    <Link
+    <button
+      type="button"
       className={classNames(styles.headerLogo, className)}
-      to="/"
+      onClick={onClick}
       aria-label={t("header_label")}
     >
       <Logo />
-    </Link>
+    </button>
   );
 };
 
@@ -142,7 +161,7 @@ export const RoomHeaderInfo: FC<RoomHeaderInfoProps> = ({
   participantCount,
 }) => {
   const { t } = useTranslation();
-  const size = useMediaQuery("(max-width: 550px)") ? "sm" : "lg";
+  const size = useRootSizeMatches(({ width }) => width <= 550) ? "sm" : "lg";
 
   return (
     <div className={styles.roomHeaderInfo} data-size={size}>
diff --git a/src/HostBridge.test.ts b/src/HostBridge.test.ts
new file mode 100644
index 000000000..fb3779f41
--- /dev/null
+++ b/src/HostBridge.test.ts
@@ -0,0 +1,306 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test, vi } from "vitest";
+import { type WidgetApi, WidgetApiToWidgetAction } from "matrix-widget-api";
+import EventEmitter from "events";
+
+import { type Observable } from "rxjs";
+
+import {
+  createWidgetHostBridge,
+  type HostBridge,
+  nullHostBridge,
+} from "./HostBridge";
+import { ElementWidgetActions, type WidgetHelpers } from "./widget";
+
+function mockWidget(api: Partial<WidgetApi>): WidgetHelpers {
+  return {
+    api: api as WidgetApi,
+    lazyActions: new EventEmitter(),
+    client: Promise.resolve(),
+  } as unknown as WidgetHelpers;
+}
+
+/** A widget whose transport records what Element Call sends it. */
+function mockTransport(): {
+  send: ReturnType<typeof vi.fn>;
+  reply: ReturnType<typeof vi.fn>;
+  stop: ReturnType<typeof vi.fn>;
+} {
+  return {
+    send: vi.fn().mockResolvedValue(undefined),
+    reply: vi.fn(),
+    stop: vi.fn(),
+  };
+}
+
+describe("createWidgetHostBridge", () => {
+  describe("telling the host what Element Call is doing", () => {
+    test("asks to be kept on screen, and to stop being", async () => {
+      const setAlwaysOnScreen = vi.fn().mockResolvedValue(true);
+      const bridge = createWidgetHostBridge(mockWidget({ setAlwaysOnScreen }));
+
+      await bridge.setAlwaysOnScreen(true);
+      await bridge.setAlwaysOnScreen(false);
+
+      expect(setAlwaysOnScreen).toHaveBeenNthCalledWith(1, true);
+      expect(setAlwaysOnScreen).toHaveBeenNthCalledWith(2, false);
+    });
+
+    test("reports that it has loaded", async () => {
+      const sendContentLoaded = vi.fn().mockResolvedValue(undefined);
+      const bridge = createWidgetHostBridge(mockWidget({ sendContentLoaded }));
+
+      await bridge.contentLoaded();
+
+      expect(sendContentLoaded).toHaveBeenCalledOnce();
+    });
+
+    test.each([
+      ["notifyJoined", ElementWidgetActions.JoinCall, {}],
+      ["notifyHungUp", ElementWidgetActions.HangupCall, {}],
+    ] as const)("sends %s as %s", async (method, action, payload) => {
+      const transport = mockTransport();
+      const bridge = createWidgetHostBridge(mockWidget({ transport } as never));
+
+      await bridge[method]();
+
+      expect(transport.send).toHaveBeenCalledWith(action, payload);
+    });
+
+    test("sends the mute state the host needs to mirror", async () => {
+      const transport = mockTransport();
+      const bridge = createWidgetHostBridge(mockWidget({ transport } as never));
+
+      await bridge.notifyDeviceMute({
+        audio_enabled: true,
+        video_enabled: false,
+      });
+
+      expect(transport.send).toHaveBeenCalledWith(
+        ElementWidgetActions.DeviceMute,
+        { audio_enabled: true, video_enabled: false },
+      );
+    });
+  });
+
+  describe("relaying what the host asks for", () => {
+    /** Emits a widget action the way widget.ts does, and returns the event. */
+    function askHost(
+      widget: WidgetHelpers,
+      action: string,
+      data: unknown,
+    ): CustomEvent {
+      const ev = new CustomEvent(action, { detail: { action, data } });
+      widget.lazyActions.emit(action, ev);
+      return ev;
+    }
+
+    // Selectors rather than keys, so each stream keeps its own request type
+    const inboundStreams: [
+      name: string,
+      select: (bridge: HostBridge) => Observable<{ data: unknown }>,
+      action: string,
+    ][] = [
+      [
+        "themeChange$",
+        (bridge) => bridge.themeChange$,
+        WidgetApiToWidgetAction.ThemeChange,
+      ],
+      ["join$", (bridge) => bridge.join$, ElementWidgetActions.JoinCall],
+      ["hangUp$", (bridge) => bridge.hangUp$, ElementWidgetActions.HangupCall],
+      [
+        "deviceMute$",
+        (bridge) => bridge.deviceMute$,
+        ElementWidgetActions.DeviceMute,
+      ],
+    ];
+
+    test.each(inboundStreams)(
+      "surfaces %s with the host's data",
+      (_name, select, action) => {
+        const widget = mockWidget({ transport: mockTransport() } as never);
+        const bridge = createWidgetHostBridge(widget);
+        const seen: unknown[] = [];
+        select(bridge).subscribe((request) => seen.push(request.data));
+
+        askHost(widget, action, { some: "payload" });
+
+        expect(seen).toEqual([{ some: "payload" }]);
+      },
+    );
+
+    test("replies to the host against the request it made", () => {
+      const transport = mockTransport();
+      const widget = mockWidget({ transport } as never);
+      const bridge = createWidgetHostBridge(widget);
+      bridge.deviceMute$.subscribe((request) =>
+        request.reply({ audio_enabled: false, video_enabled: true }),
+      );
+
+      const ev = askHost(widget, ElementWidgetActions.DeviceMute, {
+        audio_enabled: false,
+      });
+
+      expect(transport.reply).toHaveBeenCalledWith(ev.detail, {
+        audio_enabled: false,
+        video_enabled: true,
+      });
+    });
+
+    test("still replies when there is nothing to say", () => {
+      const transport = mockTransport();
+      const widget = mockWidget({ transport } as never);
+      const bridge = createWidgetHostBridge(widget);
+      bridge.hangUp$.subscribe((request) => request.reply());
+
+      const ev = askHost(widget, ElementWidgetActions.HangupCall, {});
+
+      // The widget API requires an answer, so an empty reply becomes {}
+      expect(transport.reply).toHaveBeenCalledWith(ev.detail, {});
+    });
+
+    test("stops listening once unsubscribed", () => {
+      const widget = mockWidget({ transport: mockTransport() } as never);
+      const bridge = createWidgetHostBridge(widget);
+      const seen: unknown[] = [];
+      const subscription = bridge.hangUp$.subscribe((r) => seen.push(r.data));
+
+      subscription.unsubscribe();
+      askHost(widget, ElementWidgetActions.HangupCall, {});
+
+      expect(seen).toEqual([]);
+    });
+  });
+
+  describe("downloadMedia", () => {
+    const mxcUri = "mxc://example.org/alice-avatar";
+
+    test("passes a Blob through unchanged", async () => {
+      const file = new Blob([]);
+      const bridge = createWidgetHostBridge(
+        mockWidget({ downloadFile: vi.fn().mockResolvedValue({ file }) }),
+      );
+
+      await expect(bridge.downloadMedia!(mxcUri)).resolves.toBe(file);
+    });
+
+    test("decodes a base64 string into a Blob", async () => {
+      const bridge = createWidgetHostBridge(
+        mockWidget({
+          // "hello" in base64
+          downloadFile: vi.fn().mockResolvedValue({ file: "aGVsbG8=" }),
+        }),
+      );
+
+      const blob = await bridge.downloadMedia!(mxcUri);
+
+      expect(blob).toBeInstanceOf(Blob);
+      // The five decoded bytes, rather than the eight characters of base64 —
+      // which is what we'd get if the string were stored verbatim.
+      expect(blob.size).toBe(5);
+    });
+
+    test("rejects a file format it does not understand", async () => {
+      const bridge = createWidgetHostBridge(
+        mockWidget({ downloadFile: vi.fn().mockResolvedValue({ file: 42 }) }),
+      );
+
+      await expect(bridge.downloadMedia!(mxcUri)).rejects.toThrow(
+        "Downloaded file format is not supported",
+      );
+    });
+  });
+
+  describe("close", () => {
+    test("asks the host to close, then stops the transport", async () => {
+      const transport = {
+        send: vi.fn().mockResolvedValue(undefined),
+        stop: vi.fn(),
+      };
+      const bridge = createWidgetHostBridge(mockWidget({ transport } as never));
+
+      await bridge.close!();
+
+      expect(transport.send).toHaveBeenCalledWith(
+        ElementWidgetActions.Close,
+        {},
+      );
+      expect(transport.stop).toHaveBeenCalledOnce();
+    });
+
+    test("stops the transport even when the host refuses to close", async () => {
+      const transport = {
+        send: vi.fn().mockRejectedValue(new Error("no")),
+        stop: vi.fn(),
+      };
+      const bridge = createWidgetHostBridge(mockWidget({ transport } as never));
+
+      // Leaving the messaging live would leave the close affordance dead
+      await expect(bridge.close!()).rejects.toThrow("no");
+      expect(transport.stop).toHaveBeenCalledOnce();
+    });
+  });
+
+  test("does not offer profile changes, since the host signed the user in", () => {
+    const bridge = createWidgetHostBridge(mockWidget({}));
+    expect(bridge.supportsProfileChanges).toBe(false);
+  });
+
+  test("allows joining unmuted on the intent, since the host asked for the call", () => {
+    const bridge = createWidgetHostBridge(mockWidget({}));
+    expect(bridge.allowJoinUnmutedViaIntent).toBe(true);
+  });
+
+  describe("supportsReactions", () => {
+    const capabilities = [
+      "org.matrix.msc2762.send.event:m.reaction",
+      "org.matrix.msc2762.send.event:m.room.redaction",
+      "org.matrix.msc2762.receive.event:m.reaction",
+      "org.matrix.msc2762.receive.event:m.room.redaction",
+    ];
+
+    test("is true when the host grants every reaction capability", () => {
+      const bridge = createWidgetHostBridge(
+        mockWidget({ hasCapability: () => true }),
+      );
+
+      expect(bridge.supportsReactions).toBe(true);
+    });
+
+    test.each(capabilities)("is false without %s", (missing) => {
+      const bridge = createWidgetHostBridge(
+        mockWidget({ hasCapability: (c) => c !== missing }),
+      );
+
+      expect(bridge.supportsReactions).toBe(false);
+    });
+  });
+});
+
+describe("nullHostBridge", () => {
+  test("offers no way to close, so the interface falls back to navigation", () => {
+    expect(nullHostBridge.close).toBeUndefined();
+  });
+
+  test("supports profile changes, since Element Call signed the user in itself", () => {
+    expect(nullHostBridge.supportsProfileChanges).toBe(true);
+  });
+
+  test("offers no media download, so Element Call uses its own client", () => {
+    expect(nullHostBridge.downloadMedia).toBeUndefined();
+  });
+
+  test("supports reactions, since nothing is mediating its homeserver access", () => {
+    expect(nullHostBridge.supportsReactions).toBe(true);
+  });
+
+  test("does not allow joining unmuted on the intent, since nobody vouched for it", () => {
+    expect(nullHostBridge.allowJoinUnmutedViaIntent).toBe(false);
+  });
+});
diff --git a/src/HostBridge.ts b/src/HostBridge.ts
new file mode 100644
index 000000000..2ba50257c
--- /dev/null
+++ b/src/HostBridge.ts
@@ -0,0 +1,248 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { createContext, use } from "react";
+import { fromEvent, map, NEVER, type Observable } from "rxjs";
+import {
+  type IWidgetApiRequest,
+  type IWidgetApiRequestData,
+  WidgetApiToWidgetAction,
+} from "matrix-widget-api";
+
+import {
+  ElementWidgetActions,
+  type JoinCallData,
+  type WidgetHelpers,
+} from "./widget";
+
+// Note: these are type aliases rather than interfaces so that they satisfy the
+// widget API's index-signature payload types.
+
+/** The mute state Element Call and its host exchange. */
+export type DeviceMuteState = {
+  audio_enabled: boolean;
+  video_enabled: boolean;
+};
+
+/**
+ * A mute state change requested by the host. An absent field means "leave this
+ * one as it is".
+ */
+export type DeviceMuteRequest = {
+  audio_enabled?: boolean;
+  video_enabled?: boolean;
+};
+
+/**
+ * Something the host has asked of Element Call, which it is expected to
+ * acknowledge.
+ */
+export interface HostRequest<Data, Reply = void> {
+  data: Data;
+  /** Acknowledges the request. Should be called exactly once. */
+  reply(reply: Reply): void;
+}
+
+/**
+ * Element Call's view of the application hosting it.
+ *
+ * Element Call can run as its own page, as a widget inside a Matrix client, or
+ * as a component inside one. Only the last two give it a host, and each of
+ * them reaches it by a different route — so everything Element Call needs from
+ * whatever is hosting it goes through this interface, rather than being
+ * expressed in terms of the widget API.
+ *
+ * This covers the interactions Element Call has with its host while running.
+ * The Matrix client it talks to is supplied separately, at startup.
+ */
+export interface HostBridge {
+  // What Element Call tells the host.
+
+  /**
+   * Asks the host to keep Element Call on screen (or stop doing so), so that a
+   * call in progress is not torn down when the user navigates elsewhere.
+   */
+  setAlwaysOnScreen(alwaysOnScreen: boolean): Promise<void>;
+  /** Tells the host that Element Call has finished loading. */
+  contentLoaded(): Promise<void>;
+  /** Tells the host that the user has joined the call. */
+  notifyJoined(): Promise<void>;
+  /** Tells the host that the user has hung up. */
+  notifyHungUp(): Promise<void>;
+  /** Tells the host the user's current audio and video mute state. */
+  notifyDeviceMute(state: DeviceMuteState): Promise<void>;
+  /**
+   * Asks the host to close Element Call, and stops communicating with it. No
+   * further calls should be made on this bridge afterwards.
+   *
+   * Absent when the host has no way to dismiss Element Call — standalone, the
+   * user navigates away instead — so its presence is what tells the interface
+   * whether to offer a close affordance.
+   */
+  close?(): Promise<void>;
+
+  // What the host asks of Element Call.
+
+  /** The host has changed the theme Element Call should use. */
+  themeChange$: Observable<HostRequest<{ name?: string }>>;
+  /** The host wants a preloaded Element Call to join the call now. */
+  join$: Observable<HostRequest<JoinCallData>>;
+  /** The host wants Element Call to leave the call. */
+  hangUp$: Observable<HostRequest<Record<string, never>>>;
+  /** The host wants to change, or read back, the device mute state. */
+  deviceMute$: Observable<HostRequest<DeviceMuteRequest, DeviceMuteState>>;
+
+  // What the host is, and is capable of.
+
+  /**
+   * Whether Element Call may offer to change the user's profile — their
+   * display name and avatar. Only when the account is Element Call's own,
+   * which is to say standalone: a widget's host and an application hosting
+   * the component both signed the user in themselves, so the profile is theirs
+   * to manage and Element Call must not offer to edit it.
+   */
+  readonly supportsProfileChanges: boolean;
+  /** Whether the host permits Element Call to send and receive reactions. */
+  readonly supportsReactions: boolean;
+  /**
+   * Whether the user may be put into a call unmuted on the strength of the
+   * intent alone, when the lobby is skipped and so they get no chance to check
+   * their devices first. A host that asked for the call on the user's behalf
+   * has that much of their trust; standalone Element Call does not, and starts
+   * them muted instead.
+   */
+  readonly allowJoinUnmutedViaIntent: boolean;
+  /**
+   * Fetches media on Element Call's behalf, for hosts that do not give it
+   * direct access to the homeserver. Absent when Element Call should fetch
+   * media itself using its own client.
+   */
+  downloadMedia?(mxcUri: string): Promise<Blob>;
+}
+
+/**
+ * A bridge to nowhere, for when Element Call has no host — that is, when it is
+ * running as its own page and talks to the homeserver directly.
+ */
+export const nullHostBridge: HostBridge = {
+  setAlwaysOnScreen: async () => {},
+  contentLoaded: async () => {},
+  notifyJoined: async () => {},
+  notifyHungUp: async () => {},
+  notifyDeviceMute: async () => {},
+  themeChange$: NEVER,
+  join$: NEVER,
+  hangUp$: NEVER,
+  deviceMute$: NEVER,
+  // Standalone, the account is Element Call's own: it signed the user in, so
+  // it may offer to change the profile.
+  supportsProfileChanges: true,
+  // Standalone Element Call reaches the homeserver itself, so nothing is
+  // withholding these from it.
+  supportsReactions: true,
+  // Standalone, nobody vouched for the intent: it came from a URL, which is
+  // not enough to switch the user's camera and microphone on unasked.
+  allowJoinUnmutedViaIntent: false,
+};
+
+/** Bridges to a host that Element Call is a widget of. */
+export function createWidgetHostBridge(widget: WidgetHelpers): HostBridge {
+  const requests = <Data, Reply>(
+    action: string,
+  ): Observable<HostRequest<Data, Reply>> =>
+    (
+      fromEvent(widget.lazyActions, action) as Observable<
+        CustomEvent<IWidgetApiRequest>
+      >
+    ).pipe(
+      map((ev) => ({
+        data: ev.detail.data as Data,
+        // The widget API requires a reply for every request, and carries the
+        // payload as a plain object, so an empty reply becomes {}.
+        reply: (reply: Reply): void =>
+          widget.api.transport.reply(ev.detail, reply ?? {}),
+      })),
+    );
+
+  const send = async (
+    action: ElementWidgetActions,
+    data: IWidgetApiRequestData = {},
+  ): Promise<void> => {
+    await widget.api.transport.send(action, data);
+  };
+
+  return {
+    setAlwaysOnScreen: async (alwaysOnScreen) => {
+      await widget.api.setAlwaysOnScreen(alwaysOnScreen);
+    },
+    contentLoaded: async () => widget.api.sendContentLoaded(),
+    notifyJoined: async () => send(ElementWidgetActions.JoinCall),
+    notifyHungUp: async () => send(ElementWidgetActions.HangupCall),
+    notifyDeviceMute: async (state) =>
+      send(ElementWidgetActions.DeviceMute, state),
+    close: async () => {
+      try {
+        await send(ElementWidgetActions.Close);
+      } finally {
+        // Stop regardless of whether the host acknowledged the request. A host
+        // that rejects or never answers would otherwise leave the messaging
+        // live, and the close affordance doing nothing at all.
+        widget.api.transport.stop();
+      }
+    },
+    themeChange$: requests(WidgetApiToWidgetAction.ThemeChange),
+    join$: requests(ElementWidgetActions.JoinCall),
+    hangUp$: requests(ElementWidgetActions.HangupCall),
+    deviceMute$: requests(ElementWidgetActions.DeviceMute),
+    // The client we are a widget of signed the user in, so the profile is its
+    // to manage
+    supportsProfileChanges: false,
+    // The client we are a widget of asked for this call on the user's behalf,
+    // so its intent may be trusted to say whether they start unmuted
+    allowJoinUnmutedViaIntent: true,
+    // Element Call needs the host's permission to send reactions on its behalf.
+    // Read on access rather than up front: the widget API negotiates its
+    // capabilities asynchronously, and the bridge is built before that settles.
+    get supportsReactions(): boolean {
+      return (
+        widget.api.hasCapability("org.matrix.msc2762.send.event:m.reaction") &&
+        widget.api.hasCapability(
+          "org.matrix.msc2762.send.event:m.room.redaction",
+        ) &&
+        widget.api.hasCapability(
+          "org.matrix.msc2762.receive.event:m.reaction",
+        ) &&
+        widget.api.hasCapability(
+          "org.matrix.msc2762.receive.event:m.room.redaction",
+        )
+      );
+    },
+    downloadMedia: async (mxcUri) => {
+      const { file } = await widget.api.downloadFile(mxcUri);
+      if (file instanceof Blob) return file;
+      if (typeof file === "string")
+        // it is a base64 string
+        return new Blob([Uint8Array.from(atob(file), (c) => c.charCodeAt(0))]);
+      throw new Error(
+        `Downloaded file format is not supported: ${typeof file}`,
+      );
+    },
+  };
+}
+
+const HostBridgeContext = createContext<HostBridge | null>(null);
+
+export const HostBridgeProvider = HostBridgeContext.Provider;
+
+/**
+ * The application hosting Element Call.
+ *
+ * Defaults to {@link nullHostBridge}, so that tests and stories, which have no
+ * host, need no provider.
+ */
+export const useHostBridge = (): HostBridge =>
+  use(HostBridgeContext) ?? nullHostBridge;
diff --git a/src/LeaveToHomeContext.ts b/src/LeaveToHomeContext.ts
new file mode 100644
index 000000000..4af56c216
--- /dev/null
+++ b/src/LeaveToHomeContext.ts
@@ -0,0 +1,29 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { createContext, use } from "react";
+
+/**
+ * How the user leaves the call for wherever they came from: the standalone
+ * app's home page, with its list of recent calls.
+ *
+ * The call itself has no idea where that is, or whether there is such a place
+ * at all. Standalone there is, and the shell navigates to it; as a component
+ * there is not — the host decides what happens after a call — so nothing is
+ * supplied, and the call offers no way out of its own. This is what lets the
+ * call be rendered without a router.
+ */
+const LeaveToHomeContext = createContext<(() => void) | null>(null);
+
+export const LeaveToHomeProvider = LeaveToHomeContext.Provider;
+
+/**
+ * The way out of the call, or null when there is nowhere to go and the call
+ * should not offer one.
+ */
+export const useLeaveToHome = (): (() => void) | null =>
+  use(LeaveToHomeContext);
diff --git a/src/Modal.module.css b/src/Modal.module.css
index ae8006a53..303272091 100644
--- a/src/Modal.module.css
+++ b/src/Modal.module.css
@@ -48,7 +48,7 @@ Please see LICENSE in the repository root for full details.
   --handle-inset-block-end: var(--cpd-space-4x);
 }
 
-body[data-platform="ios"] .drawer {
+[data-element-call-root][data-platform="ios"] .drawer {
   --border-radius: 10px;
   --handle-block-size: 5px;
   --handle-inline-size: 36px;
diff --git a/src/Modal.tsx b/src/Modal.tsx
index e6ffdf450..46316d370 100644
--- a/src/Modal.tsx
+++ b/src/Modal.tsx
@@ -24,6 +24,7 @@ import { Heading, Glass } from "@vector-im/compound-web";
 import styles from "./Modal.module.css";
 import overlayStyles from "./Overlay.module.css";
 import { useMediaQuery } from "./useMediaQuery";
+import { useRootElement } from "./RootElementContext";
 
 export interface Props {
   title: string;
@@ -78,6 +79,7 @@ export const Modal: FC<Props> = ({
   ...rest
 }) => {
   const { t } = useTranslation();
+  const rootElement = useRootElement();
   // Empirically, Chrome on Android can end up not matching (hover: none), but
   // still matching (pointer: coarse) :/
   const touchscreen = useMediaQuery("(hover: none) or (pointer: coarse)");
@@ -100,7 +102,7 @@ export const Modal: FC<Props> = ({
         onOpenChange={onOpenChange}
         dismissible={onDismiss !== undefined}
       >
-        <Drawer.Portal>
+        <Drawer.Portal container={rootElement}>
           <Drawer.Overlay className={classNames(overlayStyles.bg)} />
           <Drawer.Content
             className={classNames(
@@ -155,7 +157,7 @@ export const Modal: FC<Props> = ({
 
     return (
       <DialogRoot open={open} onOpenChange={onOpenChange}>
-        <DialogPortal>
+        <DialogPortal container={rootElement}>
           <DialogOverlay
             className={classNames(overlayStyles.bg, overlayStyles.animate)}
           />
diff --git a/src/QrCode.tsx b/src/QrCode.tsx
index 09bd92ea7..da5693957 100644
--- a/src/QrCode.tsx
+++ b/src/QrCode.tsx
@@ -8,7 +8,7 @@ Please see LICENSE in the repository root for full details.
 import { type FC, useEffect, useState } from "react";
 import { toDataURL } from "qrcode";
 import classNames from "classnames";
-import { t } from "i18next";
+import { useTranslation } from "react-i18next";
 
 import styles from "./QrCode.module.css";
 
@@ -18,6 +18,7 @@ interface Props {
 }
 
 export const QrCode: FC<Props> = ({ data, className }) => {
+  const { t } = useTranslation();
   const [url, setUrl] = useState<string | null>(null);
 
   useEffect(() => {
diff --git a/src/RichError.tsx b/src/RichError.tsx
index 699486e25..abacf0b34 100644
--- a/src/RichError.tsx
+++ b/src/RichError.tsx
@@ -10,7 +10,6 @@ import { PopOutIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
 
 import type { FC, ReactNode } from "react";
 import { ErrorView } from "./ErrorView";
-import { widget } from "./widget.ts";
 
 /**
  * An error consisting of a terse message to be logged to the console and a
@@ -32,11 +31,7 @@ const OpenElsewhere: FC = () => {
   const { t } = useTranslation();
 
   return (
-    <ErrorView
-      widget={widget}
-      Icon={PopOutIcon}
-      title={t("error.open_elsewhere")}
-    >
+    <ErrorView Icon={PopOutIcon} title={t("error.open_elsewhere")}>
       <p>
         {t("error.open_elsewhere_description", {
           brand: import.meta.env.VITE_PRODUCT_NAME || "Element Call",
diff --git a/src/RootElementContext.ts b/src/RootElementContext.ts
new file mode 100644
index 000000000..3eda39f51
--- /dev/null
+++ b/src/RootElementContext.ts
@@ -0,0 +1,43 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { createContext, use } from "react";
+
+/**
+ * The element that Element Call treats as the root of its own interface.
+ *
+ * Element Call decorates this element with the theme, layout and background
+ * attributes its stylesheets key off, and portals its modals into it. When
+ * Element Call owns the page this is simply the document body; as a component
+ * it is the container the host mounted it into, so that Element Call does not
+ * reach outside its own subtree.
+ *
+ * The stylesheets find this element by its `data-element-call-root` attribute,
+ * which {@link useTheme} sets along with the platform and theme, so they no
+ * longer depend on it being the body.
+ *
+ * What remains body-specific is the standalone page's own furniture: the
+ * `body` rule in `index.css` still sets the page background and margin, and
+ * `index.html` starts the body hidden with `no-theme` until the theme lands.
+ * Neither applies when a host mounts Element Call into a container of its own.
+ */
+const RootElementContext = createContext<HTMLElement | null>(null);
+
+/**
+ * Supplies the element Element Call should confine itself to. The standalone
+ * and widget builds need no provider, since for them that element is the body.
+ */
+export const RootElementProvider = RootElementContext.Provider;
+
+/**
+ * The element Element Call should decorate and portal into.
+ *
+ * Defaults to the document body, so that the standalone and widget builds work
+ * without a provider.
+ */
+export const useRootElement = (): HTMLElement =>
+  use(RootElementContext) ?? document.body;
diff --git a/src/Toast.tsx b/src/Toast.tsx
index 83e220bc1..0a2a2f1b8 100644
--- a/src/Toast.tsx
+++ b/src/Toast.tsx
@@ -25,6 +25,7 @@ import { Text } from "@vector-im/compound-web";
 
 import styles from "./Toast.module.css";
 import overlayStyles from "./Overlay.module.css";
+import { useRootElement } from "./RootElementContext";
 
 interface Props {
   /**
@@ -64,6 +65,7 @@ export const Toast: FC<Props> = ({
   Icon,
   modal = true,
 }) => {
+  const rootElement = useRootElement();
   const onOpenChange = useCallback(
     (open: boolean) => {
       if (!open) onDismiss();
@@ -104,7 +106,11 @@ export const Toast: FC<Props> = ({
 
   return (
     <DialogRoot open={open} onOpenChange={onOpenChange} modal={modal}>
-      {modal ? <DialogPortal>{content}</DialogPortal> : content}
+      {modal ? (
+        <DialogPortal container={rootElement}>{content}</DialogPortal>
+      ) : (
+        content
+      )}
     </DialogRoot>
   );
 };
diff --git a/src/UrlParams.test.ts b/src/UrlParams.test.ts
index 3a61a76b9..65be8ae85 100644
--- a/src/UrlParams.test.ts
+++ b/src/UrlParams.test.ts
@@ -11,10 +11,14 @@ import { logger } from "matrix-js-sdk/lib/logger";
 
 import * as PlatformMod from "../src/Platform";
 import {
+  BackgroundStyle,
+  configurationForIntent,
   getRoomIdentifierFromUrl,
   computeUrlParams,
   HeaderStyle,
   getUrlParams,
+  componentProperties,
+  UserIntent,
 } from "../src/UrlParams";
 import { mockConfig } from "./utils/test";
 
@@ -335,6 +339,50 @@ describe("UrlParams", () => {
         callIntent: "audio",
       });
     });
+
+    it("accepts start_call_dm_voice", () => {
+      expect(
+        computeUrlParams(
+          "?intent=start_call_dm_voice&widgetId=1234&parentUrl=parent.org",
+        ),
+      ).toMatchObject({
+        ...startNewCallDefaults("desktop"),
+        // A DM rings the other side and waits for them, whichever platform
+        sendNotificationType: "ring",
+        autoLeaveWhenOthersLeft: true,
+        waitForCallPickup: true,
+        callIntent: "audio",
+      });
+    });
+
+    it("accepts join_existing_dm", () => {
+      expect(
+        computeUrlParams(
+          "?intent=join_existing_dm&widgetId=1234&parentUrl=parent.org",
+        ),
+      ).toMatchObject({
+        ...joinExistingCallDefaults("desktop"),
+        // Straight in: the other side is already waiting
+        skipLobby: true,
+        autoLeaveWhenOthersLeft: true,
+        waitForCallPickup: false,
+        callIntent: "video",
+      });
+    });
+
+    it("accepts join_existing_dm_voice", () => {
+      expect(
+        computeUrlParams(
+          "?intent=join_existing_dm_voice&widgetId=1234&parentUrl=parent.org",
+        ),
+      ).toMatchObject({
+        ...joinExistingCallDefaults("desktop"),
+        skipLobby: true,
+        autoLeaveWhenOthersLeft: true,
+        waitForCallPickup: false,
+        callIntent: "audio",
+      });
+    });
   });
 
   describe("skipLobby", () => {
@@ -424,4 +472,48 @@ describe("UrlParams", () => {
       );
     });
   });
+
+  // What Element Call runs with when a host embeds it as a component, which
+  // has no URL of its own for any of this to come from
+  describe("hosted defaults", () => {
+    it("assume nothing about a session or a page", () => {
+      expect(componentProperties).toMatchObject({
+        // The host is not a widget host, and supplies the client itself, so
+        // none of the widget or session plumbing applies
+        isWidget: false,
+        widgetId: null,
+        parentUrl: null,
+        userId: null,
+        deviceId: null,
+        baseUrl: null,
+        homeserver: null,
+        // The gradient is drawn by a `position: fixed` pseudo-element, which
+        // would escape the container and cover the host's own interface
+        background: BackgroundStyle.Solid,
+      });
+    });
+
+    it("keep a hosted call inside its room", () => {
+      const hosted = configurationForIntent(UserIntent.JoinExistingCall);
+      expect(hosted).toMatchObject({
+        // A host owns navigation, so Element Call must not offer a way out of
+        // the room
+        confineToRoom: true,
+        perParticipantE2EE: true,
+        // The lobby first, so that the user picks their devices rather than
+        // being thrown into the call by the act of being rendered
+        skipLobby: false,
+      });
+      // No Element Call branding inside someone else's application
+      expect(hosted.header).not.toBe(HeaderStyle.Standard);
+    });
+
+    it("fall back to the standalone app's when no intent is stated", () => {
+      expect(configurationForIntent(UserIntent.Unknown)).toMatchObject({
+        confineToRoom: false,
+        header: HeaderStyle.Standard,
+        perParticipantE2EE: false,
+      });
+    });
+  });
 });
diff --git a/src/UrlParams.ts b/src/UrlParams.ts
index 805cab710..7c32c15f8 100644
--- a/src/UrlParams.ts
+++ b/src/UrlParams.ts
@@ -6,7 +6,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { useMemo } from "react";
+import { createContext, use, useMemo } from "react";
 import { useLocation } from "react-router-dom";
 import { logger } from "matrix-js-sdk/lib/logger";
 import {
@@ -59,6 +59,17 @@ export interface UrlProperties {
   // Widget api related params
   widgetId: string | null;
   parentUrl: string | null;
+  /**
+   * Whether Element Call was started as a widget of a Matrix client, which is
+   * to say whether it was given a widget ID and a parent to talk to.
+   *
+   * Only meaningful to the standalone and widget builds, which own the URL —
+   * so use it for decisions that belong to the app shell, such as whether
+   * Element Call is responsible for authenticating the user. Anything the call
+   * interface itself needs to know about its host should come from the host
+   * bridge instead.
+   */
+  isWidget: boolean;
   /**
    * Anything about what room we're pointed to should be from useRoomIdentifier which
    * parses the path and resolves alias with respect to the default server name, however
@@ -343,6 +354,136 @@ export const getUrlParams = (
   return params;
 };
 
+/**
+ * The configuration implied by what the user meant to do — if they pressed a
+ * Start Call button this would be `start_call`, and if they pressed Join Call,
+ * `join_existing`.
+ *
+ * These are platform-specific defaults, so that a host can start a call by
+ * saying what the user asked for rather than by setting every parameter itself,
+ * and so that what each intent means is Element Call's decision, made in one
+ * place. A host that wants something else states it alongside the intent.
+ *
+ * {@link UserIntent.Unknown} means no intent was stated, and gives the
+ * standalone app's defaults: Element Call owns the whole page, so it offers the
+ * way out of the room that a hosted call must not.
+ */
+export function configurationForIntent(intent: UserIntent): UrlConfiguration {
+  // Only constants and `platform` here, so that this depends on nothing but
+  // the intent.
+  let preset: UrlConfiguration = {
+    confineToRoom: true,
+    preload: false,
+    header: platform === "desktop" ? HeaderStyle.None : HeaderStyle.AppBar,
+    showControls: true,
+    hideScreensharing: false,
+    allowIceFallback: true,
+    perParticipantE2EE: true,
+    controlledAudioDevices: platform === "desktop" ? false : true,
+    skipLobby: true,
+    returnToLobby: false,
+    sendNotificationType: "notification",
+    autoLeaveWhenOthersLeft: false,
+    waitForCallPickup: false,
+  };
+  switch (intent) {
+    case UserIntent.StartNewCall:
+      preset.skipLobby = false;
+      preset.callIntent = "video";
+      break;
+    case UserIntent.JoinExistingCall:
+      // On desktop this will be overridden based on which button was used to join the call
+      preset.skipLobby = false;
+      preset.callIntent = "video";
+      break;
+    case UserIntent.StartNewCallVoice:
+      preset.skipLobby = false;
+      preset.callIntent = "audio";
+      break;
+    case UserIntent.JoinExistingCallVoice:
+      // On desktop this will be overridden based on which button was used to join the call
+      preset.skipLobby = false;
+      preset.callIntent = "audio";
+      break;
+    case UserIntent.StartNewCallDMVoice:
+      preset.callIntent = "audio";
+    // Fall through
+    case UserIntent.StartNewCallDM:
+      preset.skipLobby = true;
+      preset.sendNotificationType = "ring";
+      preset.autoLeaveWhenOthersLeft = true;
+      preset.waitForCallPickup = true;
+      preset.callIntent = preset.callIntent ?? "video";
+      break;
+    case UserIntent.JoinExistingCallDMVoice:
+      preset.callIntent = "audio";
+    // Fall through
+    case UserIntent.JoinExistingCallDM:
+      // On desktop this will be overridden based on which button was used to join the call
+      preset.skipLobby = true;
+      preset.autoLeaveWhenOthersLeft = true;
+      preset.callIntent = preset.callIntent ?? "video";
+      break;
+    // Non widget usecase defaults
+    default:
+      preset = {
+        confineToRoom: false,
+        preload: false,
+        header: HeaderStyle.Standard,
+        showControls: true,
+        hideScreensharing: false,
+        allowIceFallback: false,
+        perParticipantE2EE: false,
+        controlledAudioDevices: false,
+        skipLobby: false,
+        returnToLobby: false,
+        sendNotificationType: undefined,
+        autoLeaveWhenOthersLeft: false,
+        waitForCallPickup: false,
+      };
+  }
+  return preset;
+}
+
+/**
+ * The {@link UrlProperties} for Element Call running as a component inside a
+ * host application.
+ *
+ * It has no URL of its own to read these from, and it does not need most of
+ * them: the widget plumbing does not apply, the Matrix client and the analytics
+ * configuration come from the host by other routes, and what is left is either
+ * the host's to state through the component's props or Element Call's own
+ * default.
+ */
+export const componentProperties: UrlProperties = {
+  widgetId: null,
+  parentUrl: null,
+  isWidget: false,
+  roomId: null,
+  userId: null,
+  displayName: null,
+  deviceId: null,
+  baseUrl: null,
+  lang: null,
+  fonts: [],
+  fontScale: null,
+  posthogUserId: null,
+  posthogApiHost: null,
+  posthogApiKey: null,
+  e2eEnabled: true,
+  password: null,
+  viaServers: null,
+  homeserver: null,
+  rageshakeSubmitUrl: null,
+  sentryDsn: null,
+  sentryEnvironment: null,
+  theme: null,
+  // Solid rather than the gradient the standalone app defaults to: the gradient
+  // is drawn by a `position: fixed` pseudo-element, which would escape the
+  // container Element Call was given and cover the host's own interface.
+  background: BackgroundStyle.Solid,
+};
+
 /**
  * Gets the app parameters for the current URL.
  * @param search The URL search string
@@ -372,82 +513,12 @@ export const computeUrlParams = (search = "", hash = ""): UrlParams => {
   const intent = !isWidget
     ? UserIntent.Unknown
     : (parser.getEnumParam("intent", UserIntent) ?? UserIntent.Unknown);
-  // Here we only use constants and `platform` to determine the intent preset.
-  let intentPreset: UrlConfiguration = {
-    confineToRoom: true,
-    preload: false,
-    header: platform === "desktop" ? HeaderStyle.None : HeaderStyle.AppBar,
-    showControls: true,
-    hideScreensharing: false,
-    allowIceFallback: true,
-    perParticipantE2EE: true,
-    controlledAudioDevices: platform === "desktop" ? false : true,
-    skipLobby: true,
-    returnToLobby: false,
-    sendNotificationType: "notification",
-    autoLeaveWhenOthersLeft: false,
-    waitForCallPickup: false,
-  };
-  switch (intent) {
-    case UserIntent.StartNewCall:
-      intentPreset.skipLobby = false;
-      intentPreset.callIntent = "video";
-      break;
-    case UserIntent.JoinExistingCall:
-      // On desktop this will be overridden based on which button was used to join the call
-      intentPreset.skipLobby = false;
-      intentPreset.callIntent = "video";
-      break;
-    case UserIntent.StartNewCallVoice:
-      intentPreset.skipLobby = false;
-      intentPreset.callIntent = "audio";
-      break;
-    case UserIntent.JoinExistingCallVoice:
-      // On desktop this will be overridden based on which button was used to join the call
-      intentPreset.skipLobby = false;
-      intentPreset.callIntent = "audio";
-      break;
-    case UserIntent.StartNewCallDMVoice:
-      intentPreset.callIntent = "audio";
-    // Fall through
-    case UserIntent.StartNewCallDM:
-      intentPreset.skipLobby = true;
-      intentPreset.sendNotificationType = "ring";
-      intentPreset.autoLeaveWhenOthersLeft = true;
-      intentPreset.waitForCallPickup = true;
-      intentPreset.callIntent = intentPreset.callIntent ?? "video";
-      break;
-    case UserIntent.JoinExistingCallDMVoice:
-      intentPreset.callIntent = "audio";
-    // Fall through
-    case UserIntent.JoinExistingCallDM:
-      // On desktop this will be overridden based on which button was used to join the call
-      intentPreset.skipLobby = true;
-      intentPreset.autoLeaveWhenOthersLeft = true;
-      intentPreset.callIntent = intentPreset.callIntent ?? "video";
-      break;
-    // Non widget usecase defaults
-    default:
-      intentPreset = {
-        confineToRoom: false,
-        preload: false,
-        header: HeaderStyle.Standard,
-        showControls: true,
-        hideScreensharing: false,
-        allowIceFallback: false,
-        perParticipantE2EE: false,
-        controlledAudioDevices: false,
-        skipLobby: false,
-        returnToLobby: false,
-        sendNotificationType: undefined,
-        autoLeaveWhenOthersLeft: false,
-        waitForCallPickup: false,
-      };
-  }
+  const intentPreset = configurationForIntent(intent);
 
   const properties: UrlProperties = {
     widgetId,
     parentUrl,
+    isWidget,
     // NB. we don't validate roomId here as we do in getRoomIdentifierFromUrl:
     // what would we do if it were invalid? If the widget API says that's what
     // the room ID is, then that's what it is.
@@ -519,11 +590,37 @@ export const computeUrlParams = (search = "", hash = ""): UrlParams => {
   };
 };
 
+const UrlParamsContext = createContext<UrlParams | null>(null);
+
 /**
- * Hook to simplify use of getUrlParams.
- * @returns The app parameters for the current URL
+ * Supplies the parameters Element Call should run with.
+ *
+ * The standalone and widget builds derive these from the URL, but the
+ * component has no URL of its own to read them from, so its host provides them
+ * directly instead.
+ *
+ * TODO: `UrlParams` is no longer an accurate name now that these need not come
+ * from a URL. Renaming it touches every consumer, so it is left until the rest
+ * of the de-globalisation work has settled.
  */
-export const useUrlParams = (): UrlParams => {
+export const UrlParamsProvider = UrlParamsContext.Provider;
+
+/**
+ * The parameters Element Call is running with.
+ *
+ * Falls back to parsing `window.location` when no provider is present, so that
+ * tests and stories keep working without one.
+ */
+export const useUrlParams = (): UrlParams =>
+  use(UrlParamsContext) ?? getUrlParams();
+
+/**
+ * Derives {@link UrlParams} from the current router location.
+ *
+ * Only meaningful when Element Call owns the URL; the component is given its
+ * params directly through {@link UrlParamsProvider}.
+ */
+export const useUrlParamsFromLocation = (): UrlParams => {
   const { search, hash } = useLocation();
   return useMemo(() => getUrlParams(search, hash), [search, hash]);
 };
diff --git a/src/analytics/PosthogAnalytics.test.ts b/src/analytics/PosthogAnalytics.test.ts
index 7c1128ad4..cd821c175 100644
--- a/src/analytics/PosthogAnalytics.test.ts
+++ b/src/analytics/PosthogAnalytics.test.ts
@@ -15,6 +15,7 @@ import {
   afterAll,
 } from "vitest";
 import posthog, { type CaptureResult } from "posthog-js";
+import { type MatrixClient } from "matrix-js-sdk";
 
 import {
   Anonymity,
@@ -22,75 +23,122 @@ import {
   PosthogAnalytics,
 } from "./PosthogAnalytics";
 import { mockConfig } from "../utils/test";
+import { analyticsConfigFromEnvironment } from "../initializer";
+import { optInAnalytics } from "../settings/settings";
 
 describe("PosthogAnalytics", () => {
-  describe("embedded package", () => {
-    beforeAll(() => {
-      vi.stubEnv("VITE_PACKAGE", "embedded");
-    });
-
+  describe("enablement", () => {
     beforeEach(() => {
-      mockConfig({});
-      window.location.hash = "#";
       PosthogAnalytics.resetInstance();
     });
 
-    afterAll(() => {
-      vi.unstubAllEnvs();
-    });
-
-    it("does not create instance without config value or URL params", () => {
+    it("stays off until it is configured", () => {
       expect(PosthogAnalytics.instance.isEnabled()).toBe(false);
     });
 
-    it("ignores config value and does not create instance", () => {
-      mockConfig({
-        posthog: {
-          api_host: "https://api.example.com.localhost",
-          api_key: "api_key",
-        },
+    it("stays off when configured without credentials", () => {
+      PosthogAnalytics.configure({ matrixBackend: "jssdk" });
+      expect(PosthogAnalytics.instance.isEnabled()).toBe(false);
+    });
+
+    it("stays off when given only a key", () => {
+      PosthogAnalytics.configure({
+        matrixBackend: "jssdk",
+        apiKey: "api_key",
       });
       expect(PosthogAnalytics.instance.isEnabled()).toBe(false);
     });
 
-    it("uses URL params if both set", () => {
-      window.location.hash = `#?posthogApiHost=${encodeURIComponent("https://url.example.com.localhost")}&posthogApiKey=api_key`;
+    it("turns on when given both a key and a host", () => {
+      PosthogAnalytics.configure({
+        matrixBackend: "jssdk",
+        apiKey: "api_key",
+        apiHost: "https://api.example.com.localhost",
+      });
       expect(PosthogAnalytics.instance.isEnabled()).toBe(true);
     });
   });
 
-  describe("full package", () => {
-    beforeAll(() => {
-      vi.stubEnv("VITE_PACKAGE", "full");
-    });
-
+  // Which of the URL and config.json the credentials come from is a deliberate
+  // policy: an embedder is responsible for its own users' telemetry, so it must
+  // not pick up the deployment's, and vice versa.
+  describe("analyticsConfigFromEnvironment", () => {
     beforeEach(() => {
       mockConfig({});
       window.location.hash = "#";
-      PosthogAnalytics.resetInstance();
     });
 
     afterAll(() => {
       vi.unstubAllEnvs();
     });
 
-    it("does not create instance without config value", () => {
-      expect(PosthogAnalytics.instance.isEnabled()).toBe(false);
-    });
+    const urlCredentials = `posthogApiHost=${encodeURIComponent("https://url.example.com.localhost")}&posthogApiKey=url_key`;
+    const configCredentials = {
+      posthog: {
+        api_host: "https://config.example.com.localhost",
+        api_key: "config_key",
+      },
+    };
 
-    it("ignores URL params and does not create instance", () => {
-      window.location.hash = `#?posthogApiHost=${encodeURIComponent("https://url.example.com.localhost")}&posthogApiKey=api_key`;
-      expect(PosthogAnalytics.instance.isEnabled()).toBe(false);
-    });
-
-    it("creates instance with config value", () => {
-      mockConfig({
-        posthog: {
-          api_host: "https://api.example.com.localhost",
-          api_key: "api_key",
-        },
+    describe("embedded package", () => {
+      beforeAll(() => {
+        vi.stubEnv("VITE_PACKAGE", "embedded");
       });
-      expect(PosthogAnalytics.instance.isEnabled()).toBe(true);
+
+      it("has no credentials without URL params", () => {
+        expect(analyticsConfigFromEnvironment().apiKey).toBeUndefined();
+      });
+
+      it("takes the credentials from the URL", () => {
+        window.location.hash = `#?${urlCredentials}`;
+        expect(analyticsConfigFromEnvironment()).toMatchObject({
+          apiKey: "url_key",
+          apiHost: "https://url.example.com.localhost",
+        });
+      });
+
+      it("ignores the deployment's config", () => {
+        mockConfig(configCredentials);
+        expect(analyticsConfigFromEnvironment().apiKey).toBeUndefined();
+      });
+    });
+
+    describe("full package", () => {
+      beforeAll(() => {
+        vi.stubEnv("VITE_PACKAGE", "full");
+      });
+
+      it("has no credentials without config", () => {
+        expect(analyticsConfigFromEnvironment().apiKey).toBeUndefined();
+      });
+
+      it("takes the credentials from the config", () => {
+        mockConfig(configCredentials);
+        expect(analyticsConfigFromEnvironment()).toMatchObject({
+          apiKey: "config_key",
+          apiHost: "https://config.example.com.localhost",
+        });
+      });
+
+      it("ignores the URL params", () => {
+        window.location.hash = `#?${urlCredentials}`;
+        expect(analyticsConfigFromEnvironment().apiKey).toBeUndefined();
+      });
+    });
+
+    // Who owns the user's analytics identity depends on how Element Call is
+    // running, not on which package it was built as.
+    it("reports the embedded backend when running as a widget", () => {
+      vi.stubEnv("VITE_PACKAGE", "full");
+      window.location.hash = `#?widgetId=id&parentUrl=${encodeURIComponent("https://host.example.com.localhost")}&posthogUserId=given_id`;
+      expect(analyticsConfigFromEnvironment()).toMatchObject({
+        matrixBackend: "embedded",
+        hostAnalyticsId: "given_id",
+      });
+    });
+
+    it("reports the jssdk backend when running standalone", () => {
+      expect(analyticsConfigFromEnvironment().matrixBackend).toBe("jssdk");
     });
   });
 
@@ -204,22 +252,13 @@ describe("PosthogAnalytics", () => {
   // posthog-js bumps renaming/removing the hook. The filter logic itself is
   // covered by the applyPrivacyFilters block above.
   describe("posthog.init wiring", () => {
-    beforeAll(() => {
-      vi.stubEnv("VITE_PACKAGE", "full");
-    });
-
     beforeEach(() => {
-      mockConfig({
-        posthog: {
-          api_host: "https://api.example.com.localhost",
-          api_key: "api_key",
-        },
-      });
       PosthogAnalytics.resetInstance();
-    });
-
-    afterAll(() => {
-      vi.unstubAllEnvs();
+      PosthogAnalytics.configure({
+        matrixBackend: "jssdk",
+        apiKey: "api_key",
+        apiHost: "https://api.example.com.localhost",
+      });
     });
 
     it("passes events through the privacy filter via before_send", () => {
@@ -244,3 +283,86 @@ describe("PosthogAnalytics", () => {
     });
   });
 });
+
+describe("identifying the user", () => {
+  const credentials = {
+    apiKey: "api_key",
+    apiHost: "https://api.example.com.localhost",
+  };
+
+  function mockClient(accountDataId: string | null): MatrixClient {
+    return {
+      isGuest: () => false,
+      getCrypto: () => undefined,
+      getAccountDataFromServer: vi
+        .fn()
+        .mockResolvedValue(
+          accountDataId === null ? null : { id: accountDataId },
+        ),
+      setAccountData: vi.fn().mockResolvedValue({}),
+    } as Partial<MatrixClient> as MatrixClient;
+  }
+
+  beforeEach(() => {
+    PosthogAnalytics.resetInstance();
+    optInAnalytics.setValue(true);
+  });
+
+  it("reports under the ID its host assigned, and stores nothing", async () => {
+    const client = mockClient(null);
+    window.matrixclient = client;
+    PosthogAnalytics.configure({
+      ...credentials,
+      matrixBackend: "embedded",
+      hostAnalyticsId: "assigned-by-host",
+    });
+    const identify = vi.spyOn(posthog, "identify");
+
+    PosthogAnalytics.instance.startListeningToSettingsChanges();
+    await vi.waitFor(() =>
+      expect(identify).toHaveBeenCalledWith("assigned-by-host"),
+    );
+
+    // The host owns the user's account, so Element Call must not write to it
+    expect(client.setAccountData).not.toHaveBeenCalled();
+  });
+
+  it("keeps its own ID in account data when it owns the session", async () => {
+    const client = mockClient(null);
+    window.matrixclient = client;
+    PosthogAnalytics.configure({ ...credentials, matrixBackend: "jssdk" });
+
+    PosthogAnalytics.instance.startListeningToSettingsChanges();
+
+    // No ID on the server yet, so one is minted and stored for other devices
+    await vi.waitFor(() => expect(client.setAccountData).toHaveBeenCalled());
+  });
+
+  it("reuses the ID already in account data", async () => {
+    const client = mockClient("stored-earlier");
+    window.matrixclient = client;
+    PosthogAnalytics.configure({ ...credentials, matrixBackend: "jssdk" });
+    const identify = vi.spyOn(posthog, "identify");
+
+    PosthogAnalytics.instance.startListeningToSettingsChanges();
+    await vi.waitFor(() =>
+      expect(identify).toHaveBeenCalledWith("stored-earlier"),
+    );
+
+    expect(client.setAccountData).not.toHaveBeenCalled();
+  });
+
+  it("records how it reaches Matrix as a super property", async () => {
+    window.matrixclient = mockClient("stored-earlier");
+    PosthogAnalytics.configure({ ...credentials, matrixBackend: "embedded" });
+    const register = vi.spyOn(posthog, "register");
+
+    PosthogAnalytics.instance.startListeningToSettingsChanges();
+
+    await vi.waitFor(() =>
+      expect(register).toHaveBeenCalledWith(
+        expect.objectContaining({ matrixBackend: "embedded" }),
+      ),
+    );
+  });
+});
diff --git a/src/analytics/PosthogAnalytics.ts b/src/analytics/PosthogAnalytics.ts
index 01a146e0d..01a05bfb9 100644
--- a/src/analytics/PosthogAnalytics.ts
+++ b/src/analytics/PosthogAnalytics.ts
@@ -15,7 +15,6 @@ import { logger } from "matrix-js-sdk/lib/logger";
 import { type MatrixClient } from "matrix-js-sdk";
 import { type Subscription } from "rxjs";
 
-import { widget } from "../widget";
 import {
   CallEndedTracker,
   CallStartedTracker,
@@ -29,8 +28,6 @@ import {
   CallConnectDurationTracker,
   CallReconnectingTracker,
 } from "./PosthogEvents";
-import { Config } from "../config/Config";
-import { getUrlParams } from "../UrlParams";
 import { optInAnalytics } from "../settings/settings";
 
 /* Posthog analytics tracking.
@@ -140,6 +137,27 @@ interface PlatformProperties {
   cryptoVersion?: string;
 }
 
+/**
+ * How analytics reporting should be set up, supplied by whoever is starting
+ * Element Call rather than discovered from the page it happens to be on.
+ */
+export interface AnalyticsConfig {
+  /** The PostHog project key. Without one, analytics stay switched off. */
+  apiKey?: string;
+  apiHost?: string;
+  /**
+   * How Element Call reaches Matrix. When `embedded`, the host owns the user's
+   * identity: it supplies the analytics ID, and Element Call must not store one
+   * in the user's account data.
+   */
+  matrixBackend: "embedded" | "jssdk";
+  /** The analytics ID the host has assigned to this user, when embedded. */
+  hostAnalyticsId?: string | null;
+}
+
+/** Analytics are off until someone asks for them. */
+const analyticsDisabled: AnalyticsConfig = { matrixBackend: "jssdk" };
+
 export class PosthogAnalytics {
   /* Wrapper for Posthog analytics.
    * 3 modes of anonymity are supported, governed by this.anonymity
@@ -167,13 +185,32 @@ export class PosthogAnalytics {
   private registrationType: RegistrationType = RegistrationType.Guest;
   private optInListener: Subscription | null = null;
 
+  private static analyticsConfig: AnalyticsConfig = analyticsDisabled;
+
+  /**
+   * Sets up analytics reporting. Must be called before the instance is first
+   * used; without it, analytics stay switched off.
+   */
+  public static configure(config: AnalyticsConfig): void {
+    if (this.internalInstance)
+      // Configuration is read once, when the instance is built, so arriving
+      // late means analytics are already running unconfigured.
+      logger.warn(
+        "Analytics were configured after they had already been started; the new configuration will not take effect",
+      );
+    this.analyticsConfig = config;
+  }
+
   public static hasInstance(): boolean {
     return Boolean(this.internalInstance);
   }
 
   public static get instance(): PosthogAnalytics {
     if (!this.internalInstance) {
-      this.internalInstance = new PosthogAnalytics(posthog);
+      this.internalInstance = new PosthogAnalytics(
+        posthog,
+        PosthogAnalytics.analyticsConfig,
+      );
     }
     return this.internalInstance;
   }
@@ -181,20 +218,14 @@ export class PosthogAnalytics {
   public static resetInstance(): void {
     // Reset the singleton instance
     this.internalInstance = null;
+    this.analyticsConfig = analyticsDisabled;
   }
 
-  private constructor(private readonly posthog: PostHog) {
-    let apiKey: string | undefined;
-    let apiHost: string | undefined;
-    if (import.meta.env.VITE_PACKAGE === "embedded") {
-      // for the embedded package we always use the values from the URL as the widget host is responsible for analytics configuration
-      apiKey = getUrlParams().posthogApiKey ?? undefined;
-      apiHost = getUrlParams().posthogApiHost ?? undefined;
-    } else if (import.meta.env.VITE_PACKAGE === "full") {
-      // in full package it is the server responsible for the analytics
-      apiKey = Config.get().posthog?.api_key;
-      apiHost = Config.get().posthog?.api_host;
-    }
+  private constructor(
+    private readonly posthog: PostHog,
+    private readonly config: AnalyticsConfig,
+  ) {
+    const { apiKey, apiHost } = config;
 
     if (apiKey && apiHost) {
       const beforeSend = (event: CaptureResult | null): CaptureResult | null =>
@@ -225,15 +256,15 @@ export class PosthogAnalytics {
     }
   }
 
-  private static getPlatformProperties(): PlatformProperties {
+  private getPlatformProperties(): PlatformProperties {
     const appVersion = import.meta.env.VITE_APP_VERSION || "dev";
     return {
       appVersion,
-      matrixBackend: widget ? "embedded" : "jssdk",
+      matrixBackend: this.config.matrixBackend,
       callBackend: "livekit",
-      cryptoVersion: widget
-        ? undefined
-        : window.matrixclient?.getCrypto()?.getVersion(),
+      // Undefined when Element Call has no crypto of its own, which is the case
+      // whenever a host is doing the encrypting for it.
+      cryptoVersion: window.matrixclient?.getCrypto()?.getVersion(),
     };
   }
 
@@ -283,8 +314,8 @@ export class PosthogAnalytics {
       // different devices to send the same ID.
       let analyticsID = await this.getAnalyticsId();
       try {
-        if (!analyticsID && !widget) {
-          // only try setting up a new analytics ID in the standalone app.
+        if (!analyticsID && this.config.matrixBackend !== "embedded") {
+          // only mint an analytics ID when we are the ones storing it.
 
           // Couldn't retrieve an analytics ID from user settings, so create one and set it on the server.
           // Note there's a race condition here - if two devices do these steps at the same time, last write
@@ -313,8 +344,8 @@ export class PosthogAnalytics {
 
   private async getAnalyticsId(): Promise<string | null> {
     const client: MatrixClient = window.matrixclient;
-    if (widget) {
-      return getUrlParams().posthogUserId;
+    if (this.config.matrixBackend === "embedded") {
+      return this.config.hostAnalyticsId ?? null;
     } else {
       const accountData = await client.getAccountDataFromServer(
         PosthogAnalytics.ANALYTICS_EVENT_TYPE,
@@ -324,7 +355,7 @@ export class PosthogAnalytics {
   }
 
   private async setAccountAnalyticsId(analyticsID: string): Promise<void> {
-    if (!widget) {
+    if (this.config.matrixBackend !== "embedded") {
       const client = window.matrixclient;
 
       // the analytics ID only needs to be set in the standalone version.
@@ -362,7 +393,7 @@ export class PosthogAnalytics {
     // These properties will be subsequently passed in every event.
     //
     // This only needs to be done once per page lifetime. Note that getPlatformProperties
-    this.platformSuperProperties = PosthogAnalytics.getPlatformProperties();
+    this.platformSuperProperties = this.getPlatformProperties();
     this.registerSuperProperties({
       ...this.platformSuperProperties,
       registrationType:
diff --git a/src/auth/useInteractiveRegistration.ts b/src/auth/useInteractiveRegistration.ts
index 4972c0312..7314c9e4a 100644
--- a/src/auth/useInteractiveRegistration.ts
+++ b/src/auth/useInteractiveRegistration.ts
@@ -17,7 +17,7 @@ import { logger } from "matrix-js-sdk/lib/logger";
 import { initClient } from "../utils/matrix";
 import { type Session } from "../ClientContext";
 import { Config } from "../config/Config";
-import { widget } from "../widget";
+import { useUrlParams } from "../UrlParams";
 
 export const useInteractiveRegistration = (
   oldClient?: MatrixClient,
@@ -32,6 +32,7 @@ export const useInteractiveRegistration = (
     passwordlessUser: boolean,
   ) => Promise<[MatrixClient, Session]>;
 } => {
+  const { isWidget } = useUrlParams();
   const [privacyPolicyUrl, setPrivacyPolicyUrl] = useState<string | undefined>(
     undefined,
   );
@@ -47,7 +48,7 @@ export const useInteractiveRegistration = (
   }
 
   useEffect(() => {
-    if (widget) return;
+    if (isWidget) return;
     // An empty registerRequest is used to get the privacy policy and recaptcha key.
     authClient.current!.registerRequest({}).catch((error) => {
       setPrivacyPolicyUrl(
@@ -55,7 +56,7 @@ export const useInteractiveRegistration = (
       );
       setRecaptchaKey(error.data?.params["m.login.recaptcha"]?.public_key);
     });
-  }, []);
+  }, [isWidget]);
 
   const register = useCallback(
     async (
diff --git a/src/auth/useRegisterPasswordlessUser.ts b/src/auth/useRegisterPasswordlessUser.ts
index c2cbe2d37..27674c623 100644
--- a/src/auth/useRegisterPasswordlessUser.ts
+++ b/src/auth/useRegisterPasswordlessUser.ts
@@ -12,7 +12,7 @@ import { useClient } from "../ClientContext";
 import { useInteractiveRegistration } from "../auth/useInteractiveRegistration";
 import { generateRandomName } from "../auth/generateRandomName";
 import { useRecaptcha } from "../auth/useRecaptcha";
-import { widget } from "../widget";
+import { useUrlParams } from "../UrlParams";
 
 interface UseRegisterPasswordlessUserType {
   privacyPolicyUrl?: string;
@@ -22,6 +22,7 @@ interface UseRegisterPasswordlessUserType {
 
 export function useRegisterPasswordlessUser(): UseRegisterPasswordlessUserType {
   const { setClient } = useClient();
+  const { isWidget } = useUrlParams();
   const { privacyPolicyUrl, recaptchaKey, register } =
     useInteractiveRegistration();
   const { execute, reset, recaptchaId } = useRecaptcha(recaptchaKey);
@@ -31,7 +32,7 @@ export function useRegisterPasswordlessUser(): UseRegisterPasswordlessUserType {
       if (!setClient) {
         throw new Error("No client context");
       }
-      if (widget) {
+      if (isWidget) {
         throw new Error(
           "Registration was skipped: We should never try to register password-less user in embedded mode.",
         );
@@ -53,7 +54,7 @@ export function useRegisterPasswordlessUser(): UseRegisterPasswordlessUserType {
         throw e;
       }
     },
-    [execute, reset, register, setClient],
+    [execute, reset, register, setClient, isWidget],
   );
 
   return { privacyPolicyUrl, registerPasswordlessUser, recaptchaId };
diff --git a/src/base.css b/src/base.css
new file mode 100644
index 000000000..51751eb79
--- /dev/null
+++ b/src/base.css
@@ -0,0 +1,223 @@
+/*
+Copyright 2021-2024 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/* The styles Element Call needs wherever it is shown: the design tokens, fonts
+and element defaults its own stylesheets build on top of.
+
+Split out from index.css so that Element Call as a component can have these
+without also being given the standalone page's layout, which would style the
+host's own document. What remains here still speaks of the
+document — normalize.css and the typography below use bare element selectors,
+and the custom properties are declared on `:root` — which is right for the
+page, and is why the component build rewrites it: there every selector is
+confined to Element Call's root element (see component/build/scopeStylesToRoot.ts),
+with `html`, `body` and `:root` becoming that element. Nothing needs to be
+written differently here for that to work, but nothing here may rely on
+reaching the host's document either.
+
+Nothing here should depend on where it lands relative to Element Call's
+component stylesheets: the bundler decides that, and it decides differently for
+the app and for the component build. */
+
+@layer normalize, compound-legacy, compound;
+
+@import url("@fontsource/inter/400.css");
+@import url("@fontsource/inter/500.css");
+@import url("@fontsource/inter/600.css");
+@import url("@fontsource/inter/700.css");
+@import url("@fontsource/inconsolata/400.css");
+@import url("@fontsource/inconsolata/700.css");
+
+@import url("normalize.css/normalize.css") layer(normalize);
+@import url("@vector-im/compound-design-tokens/assets/web/css/compound-design-tokens.css") layer(compound);
+@import url("@vector-im/compound-web/dist/style.css") layer(compound.components);
+
+:root {
+  --font-scale: 1;
+  --font-size-micro: calc(10px * var(--font-scale));
+  --font-size-caption: calc(12px * var(--font-scale));
+  --font-size-body: calc(15px * var(--font-scale));
+  --font-size-subtitle: calc(18px * var(--font-scale));
+  --font-size-title: calc(24px * var(--font-scale));
+  --font-size-headline: calc(32px * var(--font-scale));
+
+  --cpd-color-border-accent: var(--cpd-color-green-800);
+  /* The distance to inset non-full-width content from the edge of Element
+  Call's root along the inline axis. This ramps up from 16px for typical mobile
+  windows, to 96px for typical desktop windows, and accounts for the safe area.
+  Container units resolve where the property is used, so this must only be used
+  by elements whose nearest query container is the root. */
+  --content-inset-left: calc(
+    env(safe-area-inset-left) +
+      min(
+        var(--cpd-space-24x),
+        max(var(--cpd-space-4x), calc((100cqw - 900px) / 3))
+      )
+  );
+  --content-inset-right: calc(
+    env(safe-area-inset-right) +
+      min(
+        var(--cpd-space-24x),
+        max(var(--cpd-space-4x), calc((100cqw - 900px) / 3))
+      )
+  );
+  --small-drop-shadow: 0px 1.2px 2.4px 0px rgba(0, 0, 0, 0.15);
+  --big-drop-shadow: 0px 0px 24px 0px #1b1d221a;
+  --subtle-drop-shadow: 0px 1px 2px 0px rgba(16, 24, 40, 0.05);
+
+  --call-view-overlay-layer: 1;
+  --call-view-header-footer-layer: 2;
+}
+
+:root,
+[class*="cpd-theme-"] {
+  --video-tile-background: var(--cpd-color-bg-subtle-secondary);
+}
+
+/* The breakpoints in Element Call's stylesheets are container queries against
+this element rather than media queries against the viewport. For the standalone
+app the two are the same thing, since the root is the page; for a host that
+embeds Element Call in a corner of its own page they are not, and it is the
+corner that the layout has to fit.
+
+For the same reason, lengths that were once a share of the viewport (`100vw`)
+are a share of the nearest query container (`100cqw`). Container units cannot
+name their container, so they only mean this element where no other query
+container — a spotlight layout, a media tile — lies in between; check that
+before using one further down the tree. */
+[data-element-call-root] {
+  container: element-call / size;
+}
+
+.cpd-theme-dark {
+  --cpd-color-border-accent: var(--cpd-color-green-1100);
+  --stopgap-color-on-solid-accent: var(--cpd-color-text-primary);
+  --stopgap-background-85: rgba(16, 19, 23, 0.85);
+}
+
+@media (min-height: 330px) {
+  [data-element-call-root][data-background="gradient"]::before {
+    content: "";
+    position: fixed;
+    /* Chromium abruptly fades our images to fully transparent at the edge of
+    the element. If we just make the element a little bigger than the viewport,
+    this is no longer visible. */
+    inset: -20px;
+    background-image: url("graphics/mobile-gradient.png");
+    background-size: 1400px 305px;
+    background-position: bottom;
+    background-repeat: no-repeat;
+  }
+
+  [data-element-call-root][data-background="gradient"][data-platform="desktop"]::before {
+    background-image: url("graphics/desktop-gradient.png");
+    background-size: max(1440px, 100cqw) max(1440px, 100cqh);
+    background-position: center;
+  }
+}
+
+/* We use this to not render the page at all until we know the theme.*/
+.no-theme {
+  opacity: 0;
+}
+
+/* On Android and iOS, prefer native system fonts. The global.css file of
+Compound Web is where these variables ultimately get consumed to set the page's
+font-family. */
+[data-element-call-root][data-platform="android"] {
+  --cpd-font-family-sans: "Roboto", "Noto", "Inter", sans-serif;
+}
+
+[data-element-call-root][data-platform="ios"] {
+  --cpd-font-family-sans:
+    -apple-system, BlinkMacSystemFont, "Inter", sans-serif;
+}
+
+@layer compound-legacy {
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6,
+  p,
+  a {
+    margin-top: 0;
+  }
+
+  /* Headline Semi Bold */
+  h1 {
+    font-weight: 600;
+    font-size: var(--font-size-headline);
+  }
+
+  /* Title */
+  h2 {
+    font-weight: 600;
+    font-size: var(--font-size-title);
+  }
+
+  /* Subtitle */
+  h3 {
+    font-weight: 600;
+    font-size: var(--font-size-subtitle);
+  }
+
+  /* Body Semi Bold */
+  h4 {
+    font-weight: 600;
+    font-size: var(--font-size-body);
+  }
+
+  h1,
+  h2,
+  h3 {
+    line-height: 1.2;
+  }
+
+  /* Body */
+  p {
+    font-size: var(--font-size-body);
+    line-height: var(--font-size-title);
+  }
+
+  hr {
+    width: calc(100% - 24px);
+    border: none;
+    border-top: 1px solid var(--cpd-color-border-interactive-secondary);
+    color: var(--cpd-color-border-interactive-secondary);
+    overflow: visible;
+    text-align: center;
+    height: 5px;
+    font-weight: 600;
+    font-size: var(--font-size-body);
+    line-height: 24px;
+    margin: 0 12px;
+  }
+
+  summary {
+    font-size: var(--font-size-body);
+  }
+
+  details > :not(summary) {
+    margin-left: var(--font-size-body);
+  }
+
+  details[open] > summary {
+    margin-bottom: var(--font-size-body);
+  }
+}
+
+/* normalize.css sets the focus rings on buttons in Firefox to an unusual custom
+outline, which is inconsistent with our other components and is not sufficiently
+visible to be accessible. This resets it back to 'auto'. */
+button:-moz-focusring,
+[type="button"]:-moz-focusring,
+[type="reset"]:-moz-focusring,
+[type="submit"]:-moz-focusring {
+  outline: auto;
+}
diff --git a/src/button/LeaveToHomeLink.tsx b/src/button/LeaveToHomeLink.tsx
new file mode 100644
index 000000000..50385a5d3
--- /dev/null
+++ b/src/button/LeaveToHomeLink.tsx
@@ -0,0 +1,40 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type FC, type MouseEvent, type ReactNode, useCallback } from "react";
+import { Link } from "@vector-im/compound-web";
+
+import { useLeaveToHome } from "../LeaveToHomeContext";
+
+interface Props {
+  className?: string;
+  children: ReactNode;
+}
+
+/**
+ * A link out of the call, to wherever the user came from. Renders nothing when
+ * there is nowhere to go (see {@link useLeaveToHome}).
+ */
+export const LeaveToHomeLink: FC<Props> = ({ className, children }) => {
+  const leaveToHome = useLeaveToHome();
+  const onClick = useCallback(
+    (e: MouseEvent<HTMLAnchorElement>) => {
+      e.preventDefault();
+      leaveToHome?.();
+    },
+    [leaveToHome],
+  );
+
+  if (leaveToHome === null) return null;
+  // Where this leads is the shell's business, so the link has no address of
+  // its own to offer
+  return (
+    <Link className={className} href="#" onClick={onClick}>
+      {children}
+    </Link>
+  );
+};
diff --git a/src/button/ReactionToggleButton.module.css b/src/button/ReactionToggleButton.module.css
index 90c6af021..4a2bd8ba8 100644
--- a/src/button/ReactionToggleButton.module.css
+++ b/src/button/ReactionToggleButton.module.css
@@ -10,7 +10,7 @@
   width: fit-content;
 }
 
-@media (max-width: 420px) {
+@container element-call (max-width: 420px) {
   .reactionPopupMenu {
     --reaction-button-padding: 8px;
     --reaction-button-fontsize: 16px;
@@ -19,7 +19,12 @@
 }
 
 div.reactionPopupMenuRoot.reactionPopupMenuModal {
-  --overlay-top: 82vh;
+  /* Down near the footer it belongs to, rather than centred like other modals.
+  A percentage, not a viewport unit: the overlay is positioned `fixed`, so this
+  resolves against the page in the standalone app and against the container
+  when a host embeds us — where 82vh would put it below the container
+  entirely. */
+  --overlay-top: 82%;
   width: fit-content;
 }
 
@@ -30,7 +35,7 @@ div.reactionPopupMenuRoot {
 
 .reactionPopupMenuRoot > div {
   width: fit-content;
-  max-width: 100vw;
+  max-width: 100cqw;
 }
 
 div.reactionPopupMenuRoot.reactionPopupMenuModal > div > div {
diff --git a/src/components/CallFooter.module.css b/src/components/CallFooter.module.css
index d919b33eb..e006a5f7d 100644
--- a/src/components/CallFooter.module.css
+++ b/src/components/CallFooter.module.css
@@ -77,7 +77,7 @@ Please see LICENSE in the repository root for full details.
 }
 
 /*First hide the logo*/
-@media (max-width: 750px) {
+@container element-call (max-width: 750px) {
   .logo {
     display: none;
   }
@@ -94,7 +94,7 @@ Please see LICENSE in the repository root for full details.
 With the logo hidden >500px is enough space to show overflow, buttons, layout.
 Once we exceed 500 we hide everything except the buttons.
 */
-@media (max-width: 500px) {
+@container element-call (max-width: 500px) {
   .footer {
     grid-template-areas: "buttons buttons buttons";
   }
@@ -115,27 +115,27 @@ Once we exceed 500 we hide everything except the buttons.
   }
 }
 
-@media (max-height: 800px) {
+@container element-call (max-height: 800px) {
   .footer {
     padding-block: var(--cpd-space-8x)
       calc(env(safe-area-inset-bottom) + var(--cpd-space-8x));
   }
 }
 
-@media (max-height: 400px) {
+@container element-call (max-height: 400px) {
   .footer {
     padding-block: var(--cpd-space-4x)
       calc(env(safe-area-inset-bottom) + var(--cpd-space-4x));
   }
 }
 
-@media (max-width: 370px) {
+@container element-call (max-width: 370px) {
   .shareScreen {
     display: none;
   }
 
   /* PIP custom css */
-  @media (max-height: 400px) {
+  @container element-call (max-height: 400px) {
     .shareScreen {
       display: flex;
     }
@@ -148,13 +148,13 @@ Once we exceed 500 we hide everything except the buttons.
   }
 }
 
-@media (max-width: 320px) {
+@container element-call (max-width: 320px) {
   .raiseHand {
     display: none;
   }
 }
 
-@media (min-width: 800px) {
+@container element-call (min-width: 800px) {
   .buttons {
     gap: var(--cpd-space-4x);
   }
diff --git a/src/components/CallFooter.stories.tsx b/src/components/CallFooter.stories.tsx
index 667cb6070..3c3f46074 100644
--- a/src/components/CallFooter.stories.tsx
+++ b/src/components/CallFooter.stories.tsx
@@ -29,7 +29,9 @@ const reactionData = {
   reactions$: new BehaviorSubject({}),
 };
 
-const mediaDevices = new MediaDevices(globalScope);
+const mediaDevices = new MediaDevices(globalScope, {
+  controlledAudioDevices: false,
+});
 
 /**
  * A wrapper component that is used for:
diff --git a/src/components/CallFooterViewModel.test.ts b/src/components/CallFooterViewModel.test.ts
index 1fc9187ad..9e73393be 100644
--- a/src/components/CallFooterViewModel.test.ts
+++ b/src/components/CallFooterViewModel.test.ts
@@ -15,6 +15,7 @@ import type { Alignment, Layout } from "../state/layout-types";
 import type { SpotlightTileViewModel } from "../state/TileViewModel";
 import type { DeviceLabel } from "../state/MediaDevices";
 import { createCallFooterViewModel } from "./CallFooterViewModel";
+import { HeaderStyle } from "../UrlParams";
 
 const platformMock = vi.hoisted(() => vi.fn(() => "desktop"));
 vi.mock("../Platform", () => ({
@@ -105,6 +106,7 @@ describe("createCallFooterViewModel", () => {
         mockMuteStates(),
         twoMicsAndOneCamMediaDevices,
         /* reactionIdentifier */ undefined,
+        { showControls: true, header: HeaderStyle.Standard },
       );
 
       expect(vm.audioOptions$.value).toEqual([]);
@@ -126,6 +128,7 @@ describe("createCallFooterViewModel", () => {
         mockMuteStates(),
         twoMicsAndOneCamMediaDevices,
         /* reactionIdentifier */ undefined,
+        { showControls: true, header: HeaderStyle.Standard },
       );
 
       expect(vm.audioOptions$?.value).toEqual([
diff --git a/src/components/CallFooterViewModel.tsx b/src/components/CallFooterViewModel.tsx
index 7e391b169..a2ca6c88e 100644
--- a/src/components/CallFooterViewModel.tsx
+++ b/src/components/CallFooterViewModel.tsx
@@ -19,7 +19,7 @@ import { type Behavior, constant } from "../state/Behavior";
 import type { ObservableScope } from "../state/ObservableScope";
 import { type MuteStates } from "../state/MuteStates";
 import { createStaticViewModel, type ViewModel } from "../state/ViewModel";
-import { getUrlParams, HeaderStyle } from "../UrlParams";
+import { HeaderStyle } from "../UrlParams";
 import { platform } from "../Platform";
 import { type FooterSnapshot } from "./CallFooter";
 
@@ -138,6 +138,8 @@ function buildDeviceBehaviors(
  * @param mediaDevices - Available and selected input devices.
  * @param reactionIdentifier - The local user's reaction identifier string, or
  *   undefined when reactions are not supported (hides the reaction button).
+ * @param options - `showControls`: whether the call controls should be shown.
+ *   `header`: the style of header, which decides whether to show the logo.
  */
 export function createCallFooterViewModel(
   scope: ObservableScope,
@@ -145,8 +147,9 @@ export function createCallFooterViewModel(
   muteStates: MuteStates,
   mediaDevices: MediaDevices,
   reactionIdentifier: string | undefined,
+  options: { showControls: boolean; header: HeaderStyle },
 ): ViewModel<FooterSnapshot> {
-  const { showControls, header: headerStyle } = getUrlParams();
+  const { showControls, header: headerStyle } = options;
   const showLogo = headerStyle === HeaderStyle.Standard;
 
   const isPip$ = scope.behavior(
diff --git a/src/components/MediaMuteAndSwitchButton.stories.tsx b/src/components/MediaMuteAndSwitchButton.stories.tsx
index 89c123929..21def4007 100644
--- a/src/components/MediaMuteAndSwitchButton.stories.tsx
+++ b/src/components/MediaMuteAndSwitchButton.stories.tsx
@@ -14,7 +14,9 @@ import { MediaDevicesContext } from "../MediaDevicesContext";
 import { MediaDevices } from "../state/MediaDevices";
 import { globalScope } from "../state/ObservableScope";
 
-const mediaDevices = new MediaDevices(globalScope);
+const mediaDevices = new MediaDevices(globalScope, {
+  controlledAudioDevices: false,
+});
 
 const meta = {
   component: MediaMuteAndSwitchButton,
diff --git a/src/config/Config.test.ts b/src/config/Config.test.ts
index 34dd44cb7..5f8b09a27 100644
--- a/src/config/Config.test.ts
+++ b/src/config/Config.test.ts
@@ -8,8 +8,8 @@ Please see LICENSE in the repository root for full details.
 import { describe, expect, it, vi, afterEach } from "vitest";
 import { logger } from "matrix-js-sdk/lib/logger";
 
-import { validateConfig } from "./Config";
-import { MatrixRTCMode } from "./ConfigOptions";
+import { Config, validateConfig } from "./Config";
+import { DEFAULT_CONFIG, MatrixRTCMode } from "./ConfigOptions";
 
 describe("validateConfig", () => {
   afterEach(() => {
@@ -52,3 +52,52 @@ describe("validateConfig", () => {
     expect(result.ssla).toBe("https://example.invalid/ssla");
   });
 });
+
+describe("Config.initWith", () => {
+  // vitest.setup.ts has already called initDefault(), so every test here is
+  // free to re-initialize; the last call wins.
+  afterEach(() => {
+    vi.restoreAllMocks();
+    Config.initDefault();
+  });
+
+  it("makes the supplied config readable", () => {
+    Config.initWith({ ssla: "https://example.invalid/ssla" });
+    expect(Config.get().ssla).toBe("https://example.invalid/ssla");
+  });
+
+  it("fills in defaults for keys the embedder did not supply", () => {
+    Config.initWith({ ssla: "https://example.invalid/ssla" });
+    expect(Config.get().media_quality).toEqual(DEFAULT_CONFIG.media_quality);
+  });
+
+  it("validates the supplied config just as a fetched one would be", () => {
+    const warnSpy = vi.spyOn(logger, "warn").mockImplementation(() => {});
+    Config.initWith({
+      matrix_rtc_mode: "nonsense" as unknown as MatrixRTCMode,
+    });
+    expect(Config.get().matrix_rtc_mode).toBeUndefined();
+    expect(warnSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it("does not share nested state with DEFAULT_CONFIG", () => {
+    Config.initWith({});
+    expect(Config.get().media_quality).not.toBe(DEFAULT_CONFIG.media_quality);
+  });
+
+  it("stops a later init() from fetching over the top of it", async () => {
+    const fetchSpy = vi.spyOn(globalThis, "fetch");
+    Config.initWith({ ssla: "https://example.invalid/ssla" });
+
+    await Config.init();
+
+    expect(fetchSpy).not.toHaveBeenCalled();
+    expect(Config.get().ssla).toBe("https://example.invalid/ssla");
+  });
+
+  it("replaces a config initialized earlier", () => {
+    Config.initWith({ ssla: "https://first.invalid/ssla" });
+    Config.initWith({ ssla: "https://second.invalid/ssla" });
+    expect(Config.get().ssla).toBe("https://second.invalid/ssla");
+  });
+});
diff --git a/src/config/Config.ts b/src/config/Config.ts
index f52b28fde..e2c5eb8fa 100644
--- a/src/config/Config.ts
+++ b/src/config/Config.ts
@@ -30,6 +30,14 @@ export class Config {
     return this.internalInstance.config;
   }
 
+  /**
+   * Initializes the config by fetching `config.json`, locating it relative to
+   * the current page.
+   *
+   * Does nothing if the config has already been initialized, including by
+   * {@link Config.initWith}, so that the regular startup path can run unchanged
+   * when a component host has already supplied the config.
+   */
   public static async init(): Promise<void> {
     if (!Config.internalInstance?.initPromise) {
       const internalInstance = new Config();
@@ -50,17 +58,35 @@ export class Config {
 
       Config.internalInstance.initPromise = downloadConfig(fetchTarget).then(
         (config) => {
-          internalInstance.config = merge(
-            {},
-            DEFAULT_CONFIG,
-            validateConfig(config),
-          );
+          internalInstance.config = resolveConfig(config);
         },
       );
     }
     return Config.internalInstance.initPromise;
   }
 
+  /**
+   * Initializes the config from an object supplied by the application hosting
+   * the component, instead of fetching `config.json`.
+   *
+   * {@link Config.init} derives the location of `config.json` from
+   * `window.location`, which only makes sense while Element Call owns the page.
+   * As a component, the host owns the configuration and passes it in here.
+   *
+   * The config goes through the same validation and defaulting as a fetched
+   * one, so that a supplied config behaves identically to a fetched one.
+   *
+   * Replaces any config initialized earlier.
+   */
+  public static initWith(config: ConfigOptions): void {
+    const internalInstance = new Config();
+    internalInstance.config = resolveConfig(config);
+    // Mark initialization as already done, so that a later init() resolves
+    // immediately rather than fetching config.json over the top of this.
+    internalInstance.initPromise = Promise.resolve();
+    Config.internalInstance = internalInstance;
+  }
+
   /**
    * This is a alternative initializer that does not load anything
    * from a hosted config file but instead just initializes the config using the
@@ -69,8 +95,7 @@ export class Config {
    * It is supposed to only be used in tests. (It is executed in `vite.setup.js`)
    */
   public static initDefault(): void {
-    Config.internalInstance = new Config();
-    Config.internalInstance.config = { ...DEFAULT_CONFIG };
+    Config.initWith({});
   }
 
   // Convenience accessors
@@ -94,6 +119,15 @@ export class Config {
   private initPromise?: Promise<void>;
 }
 
+/**
+ * Applies validation and the built-in defaults to a config, however it was
+ * obtained. Deep-merges onto a fresh object so that the result never shares
+ * nested state with {@link DEFAULT_CONFIG}.
+ */
+function resolveConfig(config: ConfigOptions): ResolvedConfigOptions {
+  return merge({}, DEFAULT_CONFIG, validateConfig(config));
+}
+
 export function validateConfig(config: ConfigOptions): ConfigOptions {
   const mode = config.matrix_rtc_mode;
   if (mode !== undefined && !VALID_MATRIX_RTC_MODES.has(mode)) {
diff --git a/src/e2ee/sharedKeyManagement.test.ts b/src/e2ee/sharedKeyManagement.test.ts
new file mode 100644
index 000000000..9d0375309
--- /dev/null
+++ b/src/e2ee/sharedKeyManagement.test.ts
@@ -0,0 +1,36 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { afterEach, describe, expect, test } from "vitest";
+
+import { getKeyForRoom, saveKeyForRoom } from "./sharedKeyManagement";
+
+const roomId = "!room:example.org";
+
+describe("getKeyForRoom", () => {
+  afterEach(() => {
+    window.location.hash = "#";
+    localStorage.clear();
+  });
+
+  test("prefers a key given in the parameters over the stored one", () => {
+    saveKeyForRoom(roomId, "stored");
+    window.location.hash = `#?roomId=${encodeURIComponent(roomId)}&password=from-the-link`;
+
+    expect(getKeyForRoom(roomId)).toBe("from-the-link");
+  });
+
+  test("falls back to the stored key", () => {
+    saveKeyForRoom(roomId, "stored");
+
+    expect(getKeyForRoom(roomId)).toBe("stored");
+  });
+
+  test("has no key to offer for a room it has never seen", () => {
+    expect(getKeyForRoom(roomId)).toBeNull();
+  });
+});
diff --git a/src/e2ee/sharedKeyManagement.ts b/src/e2ee/sharedKeyManagement.ts
index 18d007e2b..b29ede319 100644
--- a/src/e2ee/sharedKeyManagement.ts
+++ b/src/e2ee/sharedKeyManagement.ts
@@ -12,7 +12,7 @@ import {
   setLocalStorageItemReactive,
   useLocalStorage,
 } from "../useLocalStorage";
-import { getUrlParams } from "../UrlParams";
+import { getUrlParams, useUrlParams } from "../UrlParams";
 import { E2eeType } from "./e2eeType";
 import { useClient } from "../ClientContext";
 
@@ -57,19 +57,31 @@ const useRoomSharedKey = (
   return [setInitialValue ?? roomSharedKey, setRoomSharedKey];
 };
 
-export function getKeyForRoom(roomId: string): string | null {
-  const { roomId: urlRoomId, password } = getUrlParams();
-  if (roomId !== urlRoomId)
+/**
+ * The shared key for a room, preferring one supplied in the parameters Element
+ * Call was started with over whatever is in local storage.
+ */
+function keyForRoom(
+  roomId: string,
+  paramsRoomId: string | null,
+  password: string | null,
+): string | null {
+  if (roomId !== paramsRoomId)
     logger.warn(
       "requested key for a roomId which is not the current call room id (from the URL)",
       roomId,
-      urlRoomId,
+      paramsRoomId,
     );
   return (
     password ?? localStorage.getItem(getRoomSharedKeyLocalStorageKey(roomId))
   );
 }
 
+export function getKeyForRoom(roomId: string): string | null {
+  const { roomId: paramsRoomId, password } = getUrlParams();
+  return keyForRoom(roomId, paramsRoomId, password);
+}
+
 export type Unencrypted = { kind: E2eeType.NONE };
 export type SharedSecret = { kind: E2eeType.SHARED_KEY; secret: string };
 export type PerParticipantE2EE = { kind: E2eeType.PER_PARTICIPANT };
@@ -77,10 +89,15 @@ export type EncryptionSystem = Unencrypted | SharedSecret | PerParticipantE2EE;
 
 export function useRoomEncryptionSystem(roomId: string): EncryptionSystem {
   const { client } = useClient();
+  const { roomId: paramsRoomId, password } = useUrlParams();
 
   const [storedPassword] = useRoomSharedKey(
+    // TODO: this passes an already-prefixed key where a room ID is expected, so
+    // the local storage key ends up prefixed twice and never matches what
+    // saveKeyForRoom writes. Preserved as-is here to keep this commit a pure
+    // refactor; the reactive read is effectively dead until it is fixed.
     getRoomSharedKeyLocalStorageKey(roomId),
-    getKeyForRoom(roomId) ?? undefined,
+    keyForRoom(roomId, paramsRoomId, password) ?? undefined,
   );
 
   const room = client?.getRoom(roomId);
diff --git a/src/grid/OneOnOneMobileLayout.module.css b/src/grid/OneOnOneMobileLayout.module.css
index e781726c9..d07520f55 100644
--- a/src/grid/OneOnOneMobileLayout.module.css
+++ b/src/grid/OneOnOneMobileLayout.module.css
@@ -30,7 +30,7 @@ Please see LICENSE in the repository root for full details.
   block-size: 140px;
 }
 
-@media (max-width: 600px) {
+@container element-call (max-width: 600px) {
   /* Give the PiP a portrait aspect ratio */
   .pip[data-size="sm"] {
     inline-size: 88px;
diff --git a/src/grid/SpotlightExpandedLayout.module.css b/src/grid/SpotlightExpandedLayout.module.css
index d765c6fce..570b62662 100644
--- a/src/grid/SpotlightExpandedLayout.module.css
+++ b/src/grid/SpotlightExpandedLayout.module.css
@@ -25,7 +25,7 @@ Please see LICENSE in the repository root for full details.
     var(--content-inset-left);
 }
 
-@media (min-width: 600px) {
+@container element-call (min-width: 600px) {
   .pip {
     inline-size: 180px;
     block-size: 135px;
diff --git a/src/home/HomePage.tsx b/src/home/HomePage.tsx
index ca1f0ea83..e61368559 100644
--- a/src/home/HomePage.tsx
+++ b/src/home/HomePage.tsx
@@ -13,7 +13,6 @@ import { ErrorPage, LoadingPage } from "../FullScreenView";
 import { UnauthenticatedView } from "./UnauthenticatedView";
 import { RegisteredView } from "./RegisteredView";
 import { usePageTitle } from "../usePageTitle";
-import { widget } from "../widget.ts";
 
 export const HomePage: FC = () => {
   const { t } = useTranslation();
@@ -24,7 +23,7 @@ export const HomePage: FC = () => {
   if (!clientState) {
     return <LoadingPage />;
   } else if (clientState.state === "error") {
-    return <ErrorPage widget={widget} error={clientState.error} />;
+    return <ErrorPage error={clientState.error} />;
   } else {
     return clientState.authenticated ? (
       <RegisteredView client={clientState.authenticated.client} />
diff --git a/src/index.css b/src/index.css
index 77db3394c..7188f5e79 100644
--- a/src/index.css
+++ b/src/index.css
@@ -5,64 +5,11 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-@layer normalize, compound-legacy, compound;
+/* Styles for Element Call as a page of its own. The parts that apply wherever
+Element Call is shown live in base.css; these are about owning the document,
+and are not loaded when a host embeds Element Call as a component. */
 
-@import url("@fontsource/inter/400.css");
-@import url("@fontsource/inter/500.css");
-@import url("@fontsource/inter/600.css");
-@import url("@fontsource/inter/700.css");
-@import url("@fontsource/inconsolata/400.css");
-@import url("@fontsource/inconsolata/700.css");
-
-@import url("normalize.css/normalize.css") layer(normalize);
-@import url("@vector-im/compound-design-tokens/assets/web/css/compound-design-tokens.css") layer(compound);
-@import url("@vector-im/compound-web/dist/style.css") layer(compound.components);
-
-:root {
-  --font-scale: 1;
-  --font-size-micro: calc(10px * var(--font-scale));
-  --font-size-caption: calc(12px * var(--font-scale));
-  --font-size-body: calc(15px * var(--font-scale));
-  --font-size-subtitle: calc(18px * var(--font-scale));
-  --font-size-title: calc(24px * var(--font-scale));
-  --font-size-headline: calc(32px * var(--font-scale));
-
-  --cpd-color-border-accent: var(--cpd-color-green-800);
-  /* The distance to inset non-full-width content from the edge of the window
-  along the inline axis. This ramps up from 16px for typical mobile windows, to
-  96px for typical desktop windows, and accounts for the safe area. */
-  --content-inset-left: calc(
-    env(safe-area-inset-left) +
-      min(
-        var(--cpd-space-24x),
-        max(var(--cpd-space-4x), calc((100vw - 900px) / 3))
-      )
-  );
-  --content-inset-right: calc(
-    env(safe-area-inset-right) +
-      min(
-        var(--cpd-space-24x),
-        max(var(--cpd-space-4x), calc((100vw - 900px) / 3))
-      )
-  );
-  --small-drop-shadow: 0px 1.2px 2.4px 0px rgba(0, 0, 0, 0.15);
-  --big-drop-shadow: 0px 0px 24px 0px #1b1d221a;
-  --subtle-drop-shadow: 0px 1px 2px 0px rgba(16, 24, 40, 0.05);
-
-  --call-view-overlay-layer: 1;
-  --call-view-header-footer-layer: 2;
-}
-
-:root,
-[class*="cpd-theme-"] {
-  --video-tile-background: var(--cpd-color-bg-subtle-secondary);
-}
-
-.cpd-theme-dark {
-  --cpd-color-border-accent: var(--cpd-color-green-1100);
-  --stopgap-color-on-solid-accent: var(--cpd-color-text-primary);
-  --stopgap-background-85: rgba(16, 19, 23, 0.85);
-}
+@import url("./base.css");
 
 body {
   background-color: var(--cpd-color-bg-canvas-default);
@@ -74,39 +21,16 @@ body {
   -webkit-tap-highlight-color: transparent;
 }
 
-@media (min-height: 330px) {
-  body[data-background="gradient"]::before {
-    content: "";
-    position: fixed;
-    /* Chromium abruptly fades our images to fully transparent at the edge of
-    the element. If we just make the element a little bigger than the viewport,
-    this is no longer visible. */
-    inset: -20px;
-    background-image: url("graphics/mobile-gradient.png");
-    background-size: 1400px 305px;
-    background-position: bottom;
-    background-repeat: no-repeat;
-  }
-
-  body[data-background="gradient"][data-platform="desktop"]::before {
-    background-image: url("graphics/desktop-gradient.png");
-    background-size: max(1440px, 100vw) max(1440px, 100vh);
-    background-position: center;
-  }
-}
-
 /* This prohibits the view to scroll for pages smaller than 122px in width
-we use this for mobile pip webviews */
-.no-scroll-body {
+we use this for mobile pip webviews. Element Call adds this class to whatever
+it treats as its root, but it is only ever the page that should be pinned like
+this — done to a container inside a host application it would take that
+container out of the host's layout — so the selector says so. */
+body.no-scroll-body {
   position: fixed;
   width: 100%;
 }
 
-/* We use this to not render the page at all until we know the theme.*/
-.no-theme {
-  opacity: 0;
-}
-
 html,
 body,
 #root {
@@ -123,104 +47,7 @@ body,
   isolation: isolate;
 }
 
-/* On Android and iOS, prefer native system fonts. The global.css file of
-Compound Web is where these variables ultimately get consumed to set the page's
-font-family. */
-body[data-platform="android"] {
-  --cpd-font-family-sans: "Roboto", "Noto", "Inter", sans-serif;
-}
-
-body[data-platform="ios"] {
-  --cpd-font-family-sans:
-    -apple-system, BlinkMacSystemFont, "Inter", sans-serif;
-}
-
-@layer compound-legacy {
-  h1,
-  h2,
-  h3,
-  h4,
-  h5,
-  h6,
-  p,
-  a {
-    margin-top: 0;
-  }
-
-  /* Headline Semi Bold */
-  h1 {
-    font-weight: 600;
-    font-size: var(--font-size-headline);
-  }
-
-  /* Title */
-  h2 {
-    font-weight: 600;
-    font-size: var(--font-size-title);
-  }
-
-  /* Subtitle */
-  h3 {
-    font-weight: 600;
-    font-size: var(--font-size-subtitle);
-  }
-
-  /* Body Semi Bold */
-  h4 {
-    font-weight: 600;
-    font-size: var(--font-size-body);
-  }
-
-  h1,
-  h2,
-  h3 {
-    line-height: 1.2;
-  }
-
-  /* Body */
-  p {
-    font-size: var(--font-size-body);
-    line-height: var(--font-size-title);
-  }
-
-  hr {
-    width: calc(100% - 24px);
-    border: none;
-    border-top: 1px solid var(--cpd-color-border-interactive-secondary);
-    color: var(--cpd-color-border-interactive-secondary);
-    overflow: visible;
-    text-align: center;
-    height: 5px;
-    font-weight: 600;
-    font-size: var(--font-size-body);
-    line-height: 24px;
-    margin: 0 12px;
-  }
-
-  summary {
-    font-size: var(--font-size-body);
-  }
-
-  details > :not(summary) {
-    margin-left: var(--font-size-body);
-  }
-
-  details[open] > summary {
-    margin-bottom: var(--font-size-body);
-  }
-}
-
 #root > [data-overlay-container] {
   position: relative;
   height: 100%;
 }
-
-/* normalize.css sets the focus rings on buttons in Firefox to an unusual custom
-outline, which is inconsistent with our other components and is not sufficiently
-visible to be accessible. This resets it back to 'auto'. */
-button:-moz-focusring,
-[type="button"]:-moz-focusring,
-[type="reset"]:-moz-focusring,
-[type="submit"]:-moz-focusring {
-  outline: auto;
-}
diff --git a/src/initializer.tsx b/src/initializer.tsx
index 91436d100..76a7fcc39 100644
--- a/src/initializer.tsx
+++ b/src/initializer.tsx
@@ -6,12 +6,11 @@ Please see LICENSE in the repository root for full details.
 */
 
 import React from "react";
-import i18n, {
+import {
   type BackendModule,
   type ReadCallback,
   type ResourceKey,
 } from "i18next";
-import { initReactI18next } from "react-i18next";
 import LanguageDetector from "i18next-browser-languagedetector";
 import * as Sentry from "@sentry/react";
 import { logger } from "matrix-js-sdk/lib/logger";
@@ -31,10 +30,14 @@ import {
 import { getUrlParams } from "./UrlParams";
 import { Config } from "./config/Config";
 import { seedSettingsFromConfig } from "./settings/settings";
-import { platform } from "./Platform";
 import { isFailure } from "./utils/fetch";
-import { initializeWidget } from "./widget";
+import { initializeWidget, type WidgetHelpers } from "./widget";
 import { enableExtendedLivekitLogs } from "./settings/settings.ts";
+import {
+  type AnalyticsConfig,
+  PosthogAnalytics,
+} from "./analytics/PosthogAnalytics.ts";
+import { i18n, languageOfLocalePath } from "./utils/i18n.ts";
 
 // This generates a map of locale names to their URL (based on import.meta.url), which looks like this:
 // {
@@ -53,17 +56,7 @@ const getLocaleUrl = (
 ): string | undefined => locales[`../locales/${language}/${namespace}.json`];
 
 const supportedLngs = [
-  ...new Set(
-    Object.keys(locales).map((url) => {
-      // The URLs are of the form ../locales/en/app.json
-      // This extracts the language code from the URL
-      const lang = url.match(/\/([^/]+)\/[^/]+\.json$/)?.[1];
-      if (!lang) {
-        throw new Error(`Could not parse locale URL ${url}`);
-      }
-      return lang;
-    }),
-  ),
+  ...new Set(Object.keys(locales).map(languageOfLocalePath)),
 ];
 
 // A backend that fetches the locale files from the URLs generated by the glob above
@@ -98,6 +91,36 @@ const Backend = {
   },
 } satisfies BackendModule;
 
+/**
+ * Where analytics reporting is configured from.
+ *
+ * Note the two halves are decided differently, and deliberately so. *Where the
+ * PostHog credentials come from* depends on the package: an embedder passes
+ * them in through the URL because it is responsible for its own users'
+ * telemetry, whereas a standalone deployment is configured by whoever operates
+ * it. *Who owns the user's analytics identity*, on the other hand, depends on
+ * how Element Call is actually running right now — the full package can be used
+ * as a widget too.
+ */
+// Exported for testing
+export function analyticsConfigFromEnvironment(): AnalyticsConfig {
+  const { posthogApiKey, posthogApiHost, posthogUserId, isWidget } =
+    getUrlParams();
+  return {
+    matrixBackend: isWidget ? "embedded" : "jssdk",
+    hostAnalyticsId: posthogUserId,
+    ...(import.meta.env.VITE_PACKAGE === "embedded"
+      ? {
+          apiKey: posthogApiKey ?? undefined,
+          apiHost: posthogApiHost ?? undefined,
+        }
+      : {
+          apiKey: Config.get().posthog?.api_key,
+          apiHost: Config.get().posthog?.api_host,
+        }),
+  };
+}
+
 enum LoadState {
   None,
   Loading,
@@ -121,8 +144,8 @@ export class Initializer {
     return !!Initializer.internalInstance?.isInitialized;
   }
 
-  public static async initBeforeReact(): Promise<void> {
-    initializeWidget();
+  public static async initBeforeReact(): Promise<WidgetHelpers | null> {
+    const widget = initializeWidget();
 
     const polyfills: Promise<unknown>[] = [];
     if (shouldPolyfillSegmenter()) {
@@ -148,10 +171,12 @@ export class Initializer {
       document.documentElement.lang = lng;
     });
 
+    // Note: deliberately no `.use(initReactI18next)` — that would register this
+    // instance as react-i18next's global default, which is the very global we
+    // are avoiding. Components receive it through `<I18nextProvider>` instead.
     await i18n
       .use(Backend)
       .use(languageDetector)
-      .use(initReactI18next)
       .init({
         fallbackLng: "en",
         defaultNS: "app",
@@ -193,9 +218,6 @@ export class Initializer {
       );
     }
 
-    // Add the platform to the DOM, so CSS can query it
-    document.body.setAttribute("data-platform", platform);
-
     // livekit logging configuration
     setLKLogExtension((level, msg, context) => {
       // we pass a synthetic logger name of "livekit" to the rageshake to make it easier to read
@@ -207,6 +229,8 @@ export class Initializer {
     });
 
     window.setLKLogLevel = setLKLogLevel;
+
+    return widget;
   }
 
   public static init(): Promise<void> | null {
@@ -239,6 +263,7 @@ export class Initializer {
       Config.init().then(
         () => {
           seedSettingsFromConfig(Config.get().media_quality);
+          PosthogAnalytics.configure(analyticsConfigFromEnvironment());
           this.loadStates.config = LoadState.Loaded;
           this.initStep(resolve);
         },
diff --git a/src/main.tsx b/src/main.tsx
index 8f64c680a..b2f79f34e 100644
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -21,6 +21,7 @@ import { init as initRageshake } from "./settings/rageshake";
 import { Initializer } from "./initializer";
 import { AppViewModel } from "./state/AppViewModel";
 import { globalScope } from "./state/ObservableScope";
+import { getUrlParams } from "./UrlParams";
 
 initRageshake().catch((e) => {
   logger.error("Failed to initialize rageshake", e);
@@ -48,10 +49,19 @@ if (fatalError !== null) {
 }
 
 Initializer.initBeforeReact()
-  .then(() => {
+  .then((widget) => {
+    const { controlledAudioDevices, callIntent } = getUrlParams();
     root.render(
       <StrictMode>
-        <App vm={new AppViewModel(globalScope)} />
+        <App
+          vm={
+            new AppViewModel(globalScope, {
+              controlledAudioDevices,
+              callIntent,
+            })
+          }
+          widget={widget}
+        />
       </StrictMode>,
     );
   })
diff --git a/src/room/CallEndedView.module.css b/src/room/CallEndedView.module.css
index e62e93d0c..7b2dbee06 100644
--- a/src/room/CallEndedView.module.css
+++ b/src/room/CallEndedView.module.css
@@ -74,7 +74,7 @@ Please see LICENSE in the repository root for full details.
   margin-bottom: 44px;
 }
 
-@media (min-width: 800px) {
+@container element-call (min-width: 800px) {
   .logo {
     display: none;
   }
diff --git a/src/room/CallEndedView.tsx b/src/room/CallEndedView.tsx
index 4df3f297b..58417c38a 100644
--- a/src/room/CallEndedView.tsx
+++ b/src/room/CallEndedView.tsx
@@ -9,8 +9,6 @@ import { type FC, type FormEventHandler, useCallback, useState } from "react";
 import { type MatrixClient } from "matrix-js-sdk";
 import { Trans, useTranslation } from "react-i18next";
 import { Button, Heading, Text } from "@vector-im/compound-web";
-import { useNavigate } from "react-router-dom";
-import { logger } from "matrix-js-sdk/lib/logger";
 
 import styles from "./CallEndedView.module.css";
 import feedbackStyle from "../input/FeedbackInput.module.css";
@@ -19,8 +17,9 @@ import { Header, HeaderLogo, LeftNav, RightNav } from "../Header";
 import { PosthogAnalytics } from "../analytics/PosthogAnalytics";
 import { FieldRow, InputField } from "../input/Input";
 import { StarRatingInput } from "../input/StarRatingInput";
-import { Link } from "../button/Link";
 import { LinkButton } from "../button";
+import { LeaveToHomeLink } from "../button/LeaveToHomeLink";
+import { useLeaveToHome } from "../LeaveToHomeContext";
 
 interface Props {
   client: MatrixClient;
@@ -38,7 +37,7 @@ export const CallEndedView: FC<Props> = ({
   endedCallId,
 }) => {
   const { t } = useTranslation();
-  const navigate = useNavigate();
+  const leaveToHome = useLeaveToHome();
 
   const { displayName } = useProfile(client);
   const [surveySubmitted, setSurveySubmitted] = useState(false);
@@ -68,14 +67,12 @@ export const CallEndedView: FC<Props> = ({
             setSurveySubmitted(true);
           } else if (!confineToRoom) {
             // if the user already has an account immediately go back to the home screen
-            navigate("/")?.catch((error) => {
-              logger.error("Failed to navigate to /", error);
-            });
+            leaveToHome?.();
           }
         }, 1000);
       }, 1000);
     },
-    [endedCallId, navigate, isPasswordlessUser, confineToRoom, starRating],
+    [endedCallId, leaveToHome, isPasswordlessUser, confineToRoom, starRating],
   );
 
   const createAccountDialog = isPasswordlessUser && (
@@ -87,6 +84,8 @@ export const CallEndedView: FC<Props> = ({
           calls
         </p>
       </Trans>
+      {/* Only guests of the standalone app are ever passwordless, so this
+      route is always the standalone app's own. */}
       <LinkButton className={styles.callEndedButton} to="/register">
         {t("call_ended_view.create_account_button")}
       </LinkButton>
@@ -157,7 +156,10 @@ export const CallEndedView: FC<Props> = ({
         </main>
         {!confineToRoom && (
           <Text className={styles.footer}>
-            <Link to="/"> {t("call_ended_view.not_now_button")} </Link>
+            <LeaveToHomeLink>
+              {" "}
+              {t("call_ended_view.not_now_button")}{" "}
+            </LeaveToHomeLink>
           </Text>
         )}
       </div>
diff --git a/src/room/GroupCallView.test.tsx b/src/room/CallView.test.tsx
similarity index 70%
rename from src/room/GroupCallView.test.tsx
rename to src/room/CallView.test.tsx
index a5c3b0d8e..8ac920b84 100644
--- a/src/room/GroupCallView.test.tsx
+++ b/src/room/CallView.test.tsx
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-// TODO-MULTI-SFU: Restore or discard these tests. The role of GroupCallView has
+// TODO-MULTI-SFU: Restore or discard these tests. The role of CallView has
 // changed (it no longer manages the connection to the same extent), so they may
 // need extra work to adapt.
 
@@ -36,7 +36,8 @@ import userEvent, {
 import { type RelationsContainer } from "matrix-js-sdk/lib/models/relations-container";
 import { useState } from "react";
 import { TooltipProvider } from "@vector-im/compound-web";
-import { type ITransport } from "matrix-widget-api";
+import { Subject } from "rxjs";
+import { Room as LivekitRoom } from "livekit-client";
 
 import { prefetchSounds } from "../soundUtils";
 import { useAudioContext } from "../useAudioContext";
@@ -50,15 +51,19 @@ import {
   mockRtcMembership,
   MockRTCSession,
 } from "../utils/test";
-import { GroupCallView } from "./GroupCallView";
+import { CallView } from "./CallView";
 import { GroupCallErrorBoundary } from "./GroupCallErrorBoundary";
-import { ElementWidgetActions, type WidgetHelpers } from "../widget";
-import { LazyEventEmitter } from "../LazyEventEmitter";
+import {
+  type HostBridge,
+  HostBridgeProvider,
+  type HostRequest,
+  nullHostBridge,
+} from "../HostBridge";
+import { type JoinCallData } from "../widget";
 import { MatrixRTCTransportMissingError } from "../utils/errors";
 import { ProcessorProvider } from "../livekit/TrackProcessorContext";
 import { MediaDevicesContext } from "../MediaDevicesContext";
 import { constant } from "../state/Behavior";
-import { type MuteStates } from "../state/MuteStates.ts";
 
 vi.mock("../soundUtils");
 vi.mock("../useAudioContext");
@@ -117,7 +122,7 @@ beforeEach(() => {
     playSoundLooping: vi.fn(),
     soundDuration: {},
   });
-  // A trivial implementation of Active call to ensure we are testing GroupCallView exclusively here.
+  // A trivial implementation of Active call to ensure we are testing CallView exclusively here.
   (ActiveCall as MockedFunction<typeof ActiveCall>).mockImplementation(
     ({ onLeft: onLeave }) => {
       return (
@@ -133,11 +138,13 @@ beforeEach(() => {
   );
 });
 
-function createGroupCallView(
-  widget: WidgetHelpers | null,
+function createCallView(
+  hostBridge: HostBridge,
   joined = true,
   options: {
     withErrorBoundary?: boolean;
+    /** Wait for the host to say when to join, rather than joining at once. */
+    preload?: boolean;
   } = {},
 ): {
   rtcSession: MatrixRTCSession;
@@ -170,44 +177,34 @@ function createGroupCallView(
     constant([localRtcMember]),
   );
   rtcSession.joined = joined;
-  const muteState = {
-    audio: { enabled: false },
-    video: { enabled: false },
-    // TODO-MULTI-SFU: This cast isn't valid, it's likely the cause of some current test failures
-  } as unknown as MuteStates;
-  const groupCallView = (
-    <GroupCallView
+  const callView = (
+    <CallView
       client={client}
       isPasswordlessUser={false}
       confineToRoom={false}
-      preload={false}
-      skipLobby={false}
+      preload={options.preload ?? false}
+      // Straight into the (mocked) call, past the lobby
+      skipLobby
       rtcSession={rtcSession.asMockedSession()}
-      muteStates={muteState}
-      widget={widget}
-      // TODO-MULTI-SFU: Make joined and setJoined work
-      joined={true}
-      setJoined={function (value: boolean): void {}}
     />
   );
   const { getByText } = render(
     <BrowserRouter>
-      <TooltipProvider>
-        <MediaDevicesContext value={mockMediaDevices({})}>
-          <ProcessorProvider>
-            {options.withErrorBoundary ? (
-              <GroupCallErrorBoundary
-                recoveryActionHandler={vi.fn()}
-                widget={null}
-              >
-                {groupCallView}
-              </GroupCallErrorBoundary>
-            ) : (
-              groupCallView
-            )}
-          </ProcessorProvider>
-        </MediaDevicesContext>
-      </TooltipProvider>
+      <HostBridgeProvider value={hostBridge}>
+        <TooltipProvider>
+          <MediaDevicesContext value={mockMediaDevices({})}>
+            <ProcessorProvider>
+              {options.withErrorBoundary ? (
+                <GroupCallErrorBoundary recoveryActionHandler={vi.fn()}>
+                  {callView}
+                </GroupCallErrorBoundary>
+              ) : (
+                callView
+              )}
+            </ProcessorProvider>
+          </MediaDevicesContext>
+        </TooltipProvider>
+      </HostBridgeProvider>
     </BrowserRouter>,
   );
   return {
@@ -216,9 +213,9 @@ function createGroupCallView(
   };
 }
 
-test.skip("GroupCallView plays a leave sound asynchronously in SPA mode", async () => {
+test.skip("CallView plays a leave sound asynchronously in SPA mode", async () => {
   const user = userEvent.setup();
-  const { getByText, rtcSession } = createGroupCallView(null);
+  const { getByText, rtcSession } = createCallView(nullHostBridge);
   const leaveButton = getByText("Leave");
   await user.click(leaveButton);
   expect(playSound).toHaveBeenCalledWith("left");
@@ -233,14 +230,9 @@ test.skip("GroupCallView plays a leave sound asynchronously in SPA mode", async
   await waitFor(() => expect(leaveRTCSession).toHaveResolved());
 });
 
-test.skip("GroupCallView plays a leave sound synchronously in widget mode", async () => {
+test.skip("CallView plays a leave sound synchronously in widget mode", async () => {
   const user = userEvent.setup();
-  const widget = {
-    api: {
-      setAlwaysOnScreen: async () => Promise.resolve(true),
-    } as Partial<WidgetHelpers["api"]>,
-    lazyActions: new LazyEventEmitter(),
-  };
+  const hostBridge: HostBridge = { ...nullHostBridge, close: vi.fn() };
   let resolvePlaySound: () => void;
   playSound = vi
     .fn()
@@ -253,9 +245,7 @@ test.skip("GroupCallView plays a leave sound synchronously in widget mode", asyn
     soundDuration: {},
   });
 
-  const { getByText, rtcSession } = createGroupCallView(
-    widget as WidgetHelpers,
-  );
+  const { getByText, rtcSession } = createCallView(hostBridge);
   const leaveButton = getByText("Leave");
   await user.click(leaveButton);
   await flushPromises();
@@ -272,28 +262,13 @@ test.skip("GroupCallView plays a leave sound synchronously in widget mode", asyn
   expect(leaveRTCSession).toHaveBeenCalledOnce();
 });
 
-test("Should close widget when all other left and play a sound", async () => {
+test("Should ask the host to close when all other left and play a sound", async () => {
   const user = userEvent.setup();
-  let widgetClosedCalled = false;
-  const { promise: widgetClosedPromise, resolve: widgetClosedResolver } =
-    Promise.withResolvers<void>();
-  const widgetSendMock = vi.fn().mockImplementation((action: string) => {
-    if (action === ElementWidgetActions.Close) {
-      widgetClosedCalled = true;
-      widgetClosedResolver();
-    }
-  });
-  const widgetStopMock = vi.fn().mockResolvedValue(undefined);
-  const widget = {
-    api: {
-      setAlwaysOnScreen: vi.fn().mockResolvedValue(true),
-      transport: {
-        send: widgetSendMock,
-        reply: vi.fn().mockResolvedValue(undefined),
-        stop: widgetStopMock,
-      } as unknown as ITransport,
-    } as Partial<WidgetHelpers["api"]>,
-    lazyActions: new LazyEventEmitter(),
+  const close = vi.fn().mockResolvedValue(undefined);
+  const hostBridge: HostBridge = {
+    ...nullHostBridge,
+    setAlwaysOnScreen: vi.fn().mockResolvedValue(undefined),
+    close,
   };
   const resolvePlaySound = Promise.withResolvers<void>();
   playSound = vi.fn().mockReturnValue(resolvePlaySound.promise);
@@ -303,53 +278,61 @@ test("Should close widget when all other left and play a sound", async () => {
     soundDuration: {},
   });
 
-  const { getByText } = createGroupCallView(widget as WidgetHelpers);
+  const { getByText } = createCallView(hostBridge);
   const leaveButton = getByText("SimulateOtherLeft");
   await user.click(leaveButton);
   await flushPromises();
-  expect(widgetClosedCalled).toBeFalsy();
+  expect(close).not.toHaveBeenCalled();
   resolvePlaySound.resolve();
 
   expect(playSound).toHaveBeenCalledWith("left", 0);
-  await widgetClosedPromise;
-  await flushPromises();
-  expect(widgetClosedCalled).toBeTruthy();
-  expect(widgetStopMock).toHaveBeenCalledOnce();
+  await waitFor(() => expect(close).toHaveBeenCalledOnce());
 }, 80000);
 
-test("Should not close widget when auto leave due to error", async () => {
+test("Waits for the host to say when to join, when preloaded", async () => {
+  // Nothing to match device names against; the host names none anyway
+  vi.spyOn(LivekitRoom, "getLocalDevices").mockResolvedValue([]);
+  const join$ = new Subject<HostRequest<JoinCallData>>();
+  const hostBridge: HostBridge = { ...nullHostBridge, join$ };
+
+  createCallView(hostBridge, false, { preload: true });
+  await flushPromises();
+  // Past the lobby, but not in the call: the host has not asked yet
+  expect(screen.queryByText("Leave")).toBeNull();
+
+  const reply = vi.fn();
+  act(() =>
+    join$.next({ data: { audioInput: null, videoInput: null }, reply }),
+  );
+  // Then in the call, and the host told so
+  await waitFor(() => expect(reply).toHaveBeenCalledOnce());
+  expect(screen.getByText("Leave")).toBeInTheDocument();
+});
+
+test("Should not ask the host to close when auto leave due to error", async () => {
   const user = userEvent.setup();
 
-  const widgetStopMock = vi.fn().mockResolvedValue(undefined);
-  const widgetSendMock = vi.fn().mockResolvedValue(undefined);
-  const widget = {
-    api: {
-      setAlwaysOnScreen: vi.fn().mockResolvedValue(true),
-      transport: {
-        send: widgetSendMock,
-        reply: vi.fn().mockResolvedValue(undefined),
-        stop: widgetStopMock,
-      } as unknown as ITransport,
-    } as Partial<WidgetHelpers["api"]>,
-    lazyActions: new LazyEventEmitter(),
+  const close = vi.fn().mockResolvedValue(undefined);
+  const setAlwaysOnScreen = vi.fn().mockResolvedValue(undefined);
+  const hostBridge: HostBridge = {
+    ...nullHostBridge,
+    setAlwaysOnScreen,
+    close,
   };
 
-  const alwaysOnScreenSpy = vi.spyOn(widget.api, "setAlwaysOnScreen");
-
-  const { getByText } = createGroupCallView(widget as WidgetHelpers);
+  const { getByText } = createCallView(hostBridge);
   const leaveButton = getByText("SimulateErrorLeft");
   await user.click(leaveButton);
   await flushPromises();
 
   // When onLeft is called, we first set always on screen to false
-  await waitFor(() => expect(alwaysOnScreenSpy).toHaveBeenCalledWith(false));
+  await waitFor(() => expect(setAlwaysOnScreen).toHaveBeenCalledWith(false));
   await flushPromises();
-  // But then we do not close the widget automatically
-  expect(widgetStopMock).not.toHaveBeenCalledOnce();
-  expect(widgetSendMock).not.toHaveBeenCalledOnce();
+  // But then we do not ask to be closed automatically
+  expect(close).not.toHaveBeenCalled();
 });
 
-test.skip("GroupCallView leaves the session when an error occurs", async () => {
+test.skip("CallView leaves the session when an error occurs", async () => {
   (ActiveCall as MockedFunction<typeof ActiveCall>).mockImplementation(() => {
     const [error, setError] = useState<Error | null>(null);
     if (error !== null) throw error;
@@ -360,7 +343,7 @@ test.skip("GroupCallView leaves the session when an error occurs", async () => {
     );
   });
   const user = userEvent.setup();
-  const { rtcSession } = createGroupCallView(null);
+  const { rtcSession } = createCallView(nullHostBridge);
   await user.click(screen.getByRole("button", { name: "Panic!" }));
   screen.getByText("Something went wrong");
   expect(leaveRTCSession).toHaveBeenCalledWith(
@@ -370,14 +353,14 @@ test.skip("GroupCallView leaves the session when an error occurs", async () => {
   );
 });
 
-test.skip("GroupCallView shows errors that occur during joining", async () => {
+test.skip("CallView shows errors that occur during joining", async () => {
   const user = userEvent.setup();
   // This should not mock this error that deep. it should only mock the CallViewModel.
   enterRTCSession.mockRejectedValue(new MatrixRTCTransportMissingError(""));
   onTestFinished(() => {
     enterRTCSession.mockReset();
   });
-  createGroupCallView(null, false);
+  createCallView(nullHostBridge, false);
   await user.click(screen.getByRole("button", { name: "Join call" }));
   screen.getByText("Call is not supported");
 });
@@ -396,7 +379,7 @@ test("translates wrapped UnsupportedStickyEventsEndpointError to the StickyEvent
     { cause: stickyError },
   );
 
-  const { rtcSession } = createGroupCallView(null, true, {
+  const { rtcSession } = createCallView(nullHostBridge, true, {
     withErrorBoundary: true,
   });
 
@@ -408,7 +391,7 @@ test("translates wrapped UnsupportedStickyEventsEndpointError to the StickyEvent
 });
 
 test("falls back to ConnectionLostError for unrecognised membership manager errors", async () => {
-  const { rtcSession } = createGroupCallView(null, true, {
+  const { rtcSession } = createCallView(nullHostBridge, true, {
     withErrorBoundary: true,
   });
 
@@ -424,7 +407,7 @@ test("falls back to ConnectionLostError for unrecognised membership manager erro
 
 test("user can reconnect after a membership manager error", async () => {
   const user = userEvent.setup();
-  const { rtcSession } = createGroupCallView(null, true);
+  const { rtcSession } = createCallView(nullHostBridge, true);
   await act(() =>
     rtcSession.emit(MatrixRTCSessionEvent.MembershipManagerError, undefined),
   );
diff --git a/src/room/GroupCallView.tsx b/src/room/CallView.tsx
similarity index 73%
rename from src/room/GroupCallView.tsx
rename to src/room/CallView.tsx
index fbd589e78..3c34dc845 100644
--- a/src/room/GroupCallView.tsx
+++ b/src/room/CallView.tsx
@@ -28,14 +28,8 @@ import {
   MatrixRTCSessionEvent,
   type MatrixRTCSession,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { useNavigate } from "react-router-dom";
 
-import type { IWidgetApiRequest } from "matrix-widget-api";
-import {
-  ElementWidgetActions,
-  type JoinCallData,
-  type WidgetHelpers,
-} from "../widget";
+import { type JoinCallData } from "../widget";
 import { LobbyView } from "./LobbyView";
 import { type MatrixInfo } from "./VideoPreview";
 import { CallEndedView } from "./CallEndedView";
@@ -54,12 +48,7 @@ import { useRoomAvatar } from "./useRoomAvatar";
 import { useRoomName } from "./useRoomName";
 import { useJoinRule } from "./useJoinRule";
 import { InviteModal } from "./InviteModal";
-import {
-  getUrlParams,
-  HeaderStyle,
-  type UrlParams,
-  useUrlParams,
-} from "../UrlParams";
+import { HeaderStyle, type UrlParams, useUrlParams } from "../UrlParams";
 import { E2eeType } from "../e2ee/e2eeType";
 import { useAudioContext } from "../useAudioContext";
 import {
@@ -67,7 +56,6 @@ import {
   type CallEventSounds,
 } from "./CallEventAudioRenderer";
 import { useLatest } from "../useLatest";
-import { usePageTitle } from "../usePageTitle";
 import {
   ConnectionLostError,
   E2EENotSupportedError,
@@ -80,6 +68,10 @@ import { useTypedEventEmitter } from "../useEvents";
 import { muteAllAudio$ } from "../state/MuteAllAudioModel.ts";
 import { useAppBarTitle } from "../AppBar.tsx";
 import { useBehavior } from "../useBehavior.ts";
+import { useRootElement } from "../RootElementContext.ts";
+import { useHostBridge } from "../HostBridge.ts";
+import { useMuteStates } from "../state/useMuteStates.ts";
+import { useLeaveToHome } from "../LeaveToHomeContext.ts";
 
 /**
  * If there already are this many participants in the call, we automatically mute
@@ -94,19 +86,67 @@ declare global {
 }
 
 interface Props {
+  /** The client to place the call with. */
   client: MatrixClient;
-  isPasswordlessUser: boolean;
-  confineToRoom: boolean;
-  preload: UrlParams["preload"];
-  skipLobby: UrlParams["skipLobby"];
+  /** The call to join. */
   rtcSession: MatrixRTCSession;
+  /**
+   * Whether the user is signed in as a guest, and so should be offered the
+   * chance to create an account when the call ends.
+   */
+  isPasswordlessUser: boolean;
+  /** Whether to keep the user in this call rather than letting them navigate. */
+  confineToRoom: boolean;
+  /** Whether to wait for the host to ask us to join. */
+  preload: UrlParams["preload"];
+  /** Whether to enter the call directly, without showing the lobby first. */
+  skipLobby: UrlParams["skipLobby"];
+}
+
+/**
+ * A call, from start to finish.
+ *
+ * This owns the whole lifecycle of being in a call: the lobby, where the user
+ * checks their camera and microphone before joining; the call itself; and the
+ * screen shown once it has ended. Not every call has every stage — the lobby
+ * is skipped when the user is put straight into the call, or when the host
+ * wants to say when to join; and after the call there may be a post-call
+ * screen, a return to the lobby, or nothing, depending on whether the host
+ * decides what comes next. The view decides which stages apply from the
+ * parameters it was started with and from what the host bridge says.
+ *
+ * It owns nothing about how Element Call came to be showing a call: no
+ * routing, no authentication, no resolving of room aliases. Those belong to
+ * whatever is hosting it — the standalone app's own shell, or an application
+ * embedding Element Call as a component. Both render this.
+ */
+export const CallView: FC<Props> = (props): ReactNode => {
+  // Whether the user is in the call is the call's own business, not its host's.
+  // Held here rather than below so that it survives the mute state being
+  // rebuilt.
+  const [joined, setJoined] = useState(false);
+  const muteStates = useMuteStates();
+
+  if (muteStates === null) return null;
+
+  return (
+    <LoadedCallView
+      {...props}
+      joined={joined}
+      setJoined={setJoined}
+      muteStates={muteStates}
+    />
+  );
+};
+
+interface LoadedProps extends Props {
   joined: boolean;
   setJoined: (value: boolean) => void;
   muteStates: MuteStates;
-  widget: WidgetHelpers | null;
 }
 
-export const GroupCallView: FC<Props> = ({
+/** {@link CallView}, once it has the mute state everything below needs. */
+const LoadedCallView: FC<LoadedProps> = ({
   client,
   isPasswordlessUser,
   confineToRoom,
@@ -116,13 +156,19 @@ export const GroupCallView: FC<Props> = ({
   joined,
   setJoined,
   muteStates,
-  widget,
 }) => {
   // Used to thread through any errors that occur outside the error boundary
   const [externalError, setExternalError] = useState<ElementCallError | null>(
     null,
   );
   const memberships = useMatrixRTCSessionMemberships(rtcSession);
+  const rootElement = useRootElement();
+  const hostBridge = useHostBridge();
+  // A host that can close us is a host that decides when we stop existing, so
+  // we neither show our own post-call screens nor assume we have time to
+  // finish what we are doing. (Whose account the user's is, by contrast, is
+  // stated outright: see `HostBridge.supportsProfileChanges`.)
+  const hostControlsLifetime = hostBridge.close !== undefined;
 
   const muteAllAudio = useBehavior(muteAllAudio$);
   const leaveSoundContext = useLatest(
@@ -140,9 +186,9 @@ export const GroupCallView: FC<Props> = ({
   }, []);
 
   useEffect(() => {
-    logger.info("[Lifecycle] GroupCallView Component mounted");
+    logger.info("[Lifecycle] CallView Component mounted");
     return (): void => {
-      logger.info("[Lifecycle] GroupCallView Component unmounted");
+      logger.info("[Lifecycle] CallView Component unmounted");
     };
   }, []);
 
@@ -150,11 +196,11 @@ export const GroupCallView: FC<Props> = ({
   // viewport sizes smaller than 122px width. (It is actually this exact number: 122px
   // tested on different devices...)
   useEffect(() => {
-    document.body.classList.add("no-scroll-body");
+    rootElement.classList.add("no-scroll-body");
     return (): void => {
-      document.body.classList.remove("no-scroll-body");
+      rootElement.classList.remove("no-scroll-body");
     };
-  }, []);
+  }, [rootElement]);
 
   useEffect(() => {
     window.rtcSession = rtcSession;
@@ -209,7 +255,6 @@ export const GroupCallView: FC<Props> = ({
     if (passwordFromUrl) saveKeyForRoom(room.roomId, passwordFromUrl);
   }, [passwordFromUrl, room.roomId]);
 
-  usePageTitle(roomName);
   useAppBarTitle(roomName);
 
   const matrixInfo = useMemo((): MatrixInfo => {
@@ -297,28 +342,26 @@ export const GroupCallView: FC<Props> = ({
     };
 
     if (skipLobby) {
-      if (widget && preload) {
+      // `preload` is only ever set when we have a host to be preloaded by.
+      if (preload) {
         // In preload mode without lobby we wait for a join action before entering
-        const onJoin = (ev: CustomEvent<IWidgetApiRequest>): void => {
+        const subscription = hostBridge.join$.subscribe(({ data, reply }) => {
           (async (): Promise<void> => {
-            await defaultDeviceSetup(ev.detail.data as unknown as JoinCallData);
+            await defaultDeviceSetup(data);
             setJoined(true);
-            widget.api.transport.reply(ev.detail, {});
+            reply();
           })().catch((e) => {
             logger.error("Error joining RTC session on preload", e);
           });
-        };
-        widget.lazyActions.on(ElementWidgetActions.JoinCall, onJoin);
-        return (): void => {
-          widget.lazyActions.off(ElementWidgetActions.JoinCall, onJoin);
-        };
+        });
+        return (): void => subscription.unsubscribe();
       } else {
         // No lobby and no preload: we enter the rtc session right away
         setJoined(true);
       }
     }
   }, [
-    widget,
+    hostBridge,
     rtcSession,
     preload,
     skipLobby,
@@ -331,7 +374,7 @@ export const GroupCallView: FC<Props> = ({
   // TODO refactor this + "joined" to just one callState
   const [left, setLeft] = useState(false);
 
-  const navigate = useNavigate();
+  const leaveToHome = useLeaveToHome();
 
   // TODO split this into leave and onDisconnect
   const onLeft = useCallback(
@@ -344,7 +387,7 @@ export const GroupCallView: FC<Props> = ({
           // When "allOthersLeft", the leaveSoundEffect$ in CallEventAudioRenderer
           // already plays the "left" sound when the remote participant's media
           // disappears. We play it here silenced (volumeOverwrite = 0) so we have the right duration in the audioPromise.
-          // (used to destory the widget)
+          // (which is what delays asking the host to close us)
           audioPromise = leaveSoundContext.current?.playSound("left", 0);
           break;
         case "timeout":
@@ -359,12 +402,12 @@ export const GroupCallView: FC<Props> = ({
       setLeft(true);
 
       // We need to wait until the callEnded event is tracked on PostHog,
-      // otherwise the iframe may get killed first.
+      // otherwise we may be torn down first.
       const posthogRequest = new Promise((resolve) => {
-        // To increase the likelihood of the PostHog event being sent out in
-        // widget mode before the iframe is killed, we ask it to skip the
-        // usual queuing/batching of requests.
-        const sendInstantly = widget !== null;
+        // To increase the likelihood of the PostHog event being sent out
+        // before the host disposes of us, we ask it to skip the usual
+        // queuing/batching of requests.
+        const sendInstantly = hostControlsLifetime;
         PosthogAnalytics.instance.eventCallEnded.track(
           room.roomId,
           rtcSession.memberships.length,
@@ -372,8 +415,8 @@ export const GroupCallView: FC<Props> = ({
           rtcSession,
         );
         // Unfortunately the PostHog library provides no way to await the
-        // tracking of an event, but we don't really want it to hold up the
-        // closing of the widget that long anyway, so giving it 10 ms will do.
+        // tracking of an event, but we don't really want it to hold up our
+        // disposal that long anyway, so giving it 10 ms will do.
         window.setTimeout(resolve, 10);
       });
 
@@ -390,27 +433,21 @@ export const GroupCallView: FC<Props> = ({
             !confineToRoom &&
             !PosthogAnalytics.instance.isEnabled()
           )
-            void navigate("/");
+            leaveToHome?.();
 
-          if (widget) {
-            // After this point the iframe could die at any moment!
+          // After this point the host could dispose of us at any moment!
+          try {
+            await hostBridge.setAlwaysOnScreen(false);
+          } catch (e) {
+            logger.error("Failed to set `alwaysOnScreen` to false", e);
+          }
+          // On a normal user hangup we can shut down and ask to be closed. But
+          // if an error occurs we should stay open until the user reads it.
+          if (reason != "error" && !returnToLobby) {
             try {
-              await widget.api.setAlwaysOnScreen(false);
+              await hostBridge.close?.();
             } catch (e) {
-              logger.error(
-                "Failed to set call widget `alwaysOnScreen` to false",
-                e,
-              );
-            }
-            // On a normal user hangup we can shut down and close the widget. But if an
-            // error occurs we should keep the widget open until the user reads it.
-            if (reason != "error" && !getUrlParams().returnToLobby) {
-              try {
-                await widget.api.transport.send(ElementWidgetActions.Close, {});
-              } catch (e) {
-                logger.error("Failed to send close action", e);
-              }
-              widget.api.transport.stop();
+              logger.error("Failed to ask the host to close Element Call", e);
             }
           }
         });
@@ -418,22 +455,24 @@ export const GroupCallView: FC<Props> = ({
     [
       setJoined,
       leaveSoundContext,
-      widget,
+      hostBridge,
+      hostControlsLifetime,
       room.roomId,
       rtcSession,
       isPasswordlessUser,
       confineToRoom,
-      navigate,
+      returnToLobby,
+      leaveToHome,
     ],
   );
 
   useEffect(() => {
-    if (widget && joined)
-      // set widget to sticky once joined.
-      widget.api.setAlwaysOnScreen(true).catch((e) => {
+    if (joined)
+      // ask to be kept on screen once joined.
+      hostBridge.setAlwaysOnScreen(true).catch((e) => {
         logger.error("Error calling setAlwaysOnScreen(true)", e);
       });
-  }, [widget, joined, rtcSession]);
+  }, [hostBridge, joined, rtcSession]);
 
   const joinRule = useJoinRule(room);
 
@@ -503,19 +542,16 @@ export const GroupCallView: FC<Props> = ({
         />
       </>
     );
-  } else if (left && widget === null) {
-    // Left in SPA mode:
+  } else if (left && !hostControlsLifetime) {
+    // Left, and it is up to us what to show next:
 
     // The call ended view is shown for two reasons: prompting guests to create
     // an account, and prompting users that have opted into analytics to provide
-    // feedback. We don't show a feedback prompt to widget users however (at
-    // least for now), because we don't yet have designs that would allow widget
-    // users to dismiss the feedback prompt and close the call window without
-    // submitting anything.
-    if (
-      isPasswordlessUser ||
-      (PosthogAnalytics.instance.isEnabled() && widget === null)
-    ) {
+    // feedback. We don't show a feedback prompt when a host owns our lifetime
+    // however (at least for now), because we don't yet have designs that would
+    // allow those users to dismiss the feedback prompt and close the call
+    // window without submitting anything.
+    if (isPasswordlessUser || PosthogAnalytics.instance.isEnabled()) {
       body = (
         <CallEndedView
           endedCallId={rtcSession.room.roomId}
@@ -531,8 +567,8 @@ export const GroupCallView: FC<Props> = ({
       // LobbyView again which would open capture devices again.
       body = null;
     }
-  } else if (left && widget !== null) {
-    // Left in widget mode:
+  } else if (left && hostControlsLifetime) {
+    // Left, and the host decides what happens next:
     body = returnToLobby ? lobbyView : null;
   } else if (preload || skipLobby) {
     // The RTC session is not joined to yet (`isJoined`), but enterRTCSessionOrError should have been called.
@@ -543,7 +579,6 @@ export const GroupCallView: FC<Props> = ({
 
   return (
     <GroupCallErrorBoundary
-      widget={widget}
       recoveryActionHandler={async (action) => {
         setExternalError(null);
         if (action == "reconnect") {
@@ -555,9 +590,10 @@ export const GroupCallView: FC<Props> = ({
       }}
       onError={(_error) => {
         if (rtcSession.isJoined()) onLeft("error");
-        // If there is an error we need to be able to close the widget. This is done in `onLeft` as well
-        // We need it here explicitly in case rtcSession.isJoined is false.
-        void widget?.api.setAlwaysOnScreen(false);
+        // If there is an error we need to be dismissible again. This is done in
+        // `onLeft` as well; we need it here explicitly in case
+        // rtcSession.isJoined is false.
+        void hostBridge.setAlwaysOnScreen(false);
       }}
     >
       {body}
diff --git a/src/room/GroupCallErrorBoundary.test.tsx b/src/room/GroupCallErrorBoundary.test.tsx
index e10044ae1..b6d903d8a 100644
--- a/src/room/GroupCallErrorBoundary.test.tsx
+++ b/src/room/GroupCallErrorBoundary.test.tsx
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { describe, expect, test, vi } from "vitest";
+import { describe, expect, onTestFinished, test, vi } from "vitest";
 import { render, screen } from "@testing-library/react";
 import {
   type FC,
@@ -14,7 +14,7 @@ import {
   useCallback,
   useState,
 } from "react";
-import { BrowserRouter } from "react-router-dom";
+import { LeaveToHomeProvider } from "../LeaveToHomeContext";
 import userEvent from "@testing-library/user-event";
 import { ConnectionError } from "livekit-client";
 import { MatrixError } from "matrix-js-sdk";
@@ -36,7 +36,14 @@ import {
   UnknownCallError,
 } from "../utils/errors.ts";
 import { mockConfig } from "../utils/test.ts";
-import { ElementWidgetActions, type WidgetHelpers } from "../widget.ts";
+import {
+  type HostBridge,
+  HostBridgeProvider,
+  nullHostBridge,
+} from "../HostBridge.ts";
+
+// Somewhere to go home to, so that the error pages offer the way
+const leaveToHome = vi.fn();
 
 test.each([
   {
@@ -75,15 +82,14 @@ test.each([
 
     const onErrorMock = vi.fn();
     const { asFragment } = render(
-      <BrowserRouter>
+      <LeaveToHomeProvider value={leaveToHome}>
         <GroupCallErrorBoundary
           onError={onErrorMock}
           recoveryActionHandler={vi.fn()}
-          widget={null}
         >
           <TestComponent />
         </GroupCallErrorBoundary>
-      </BrowserRouter>,
+      </LeaveToHomeProvider>,
     );
 
     await screen.findByText(expectedTitle);
@@ -103,16 +109,19 @@ test("should render the error page with link back to home", async () => {
   };
 
   const onErrorMock = vi.fn();
+  // From the home page itself the home button reloads instead of navigating,
+  // so be somewhere else for this test
+  window.history.pushState({}, "", "/room/somewhere");
+  onTestFinished(() => window.history.pushState({}, "", "/"));
   const { asFragment } = render(
-    <BrowserRouter>
+    <LeaveToHomeProvider value={leaveToHome}>
       <GroupCallErrorBoundary
         onError={onErrorMock}
         recoveryActionHandler={vi.fn()}
-        widget={null}
       >
         <TestComponent />
       </GroupCallErrorBoundary>
-    </BrowserRouter>,
+    </LeaveToHomeProvider>,
   );
 
   await screen.findByText("Call is not supported");
@@ -121,7 +130,11 @@ test("should render the error page with link back to home", async () => {
     screen.getByText(/Error Code: MISSING_MATRIX_RTC_TRANSPORT/i),
   ).toBeInTheDocument();
 
-  await screen.findByRole("button", { name: "Return to home screen" });
+  // The way home is whatever the shell supplied, not a route of the call's own
+  await userEvent
+    .setup()
+    .click(screen.getByRole("button", { name: "Return to home screen" }));
+  expect(leaveToHome).toHaveBeenCalledOnce();
 
   expect(onErrorMock).toHaveBeenCalledOnce();
   expect(onErrorMock).toHaveBeenCalledWith(error);
@@ -153,14 +166,11 @@ test("ConnectionLostError: Action handling should reset error state", async () =
     );
 
     return (
-      <BrowserRouter>
-        <GroupCallErrorBoundary
-          recoveryActionHandler={reconnectCallback}
-          widget={null}
-        >
+      <LeaveToHomeProvider value={leaveToHome}>
+        <GroupCallErrorBoundary recoveryActionHandler={reconnectCallback}>
           <TestComponent fail={failState} />
         </GroupCallErrorBoundary>
-      </BrowserRouter>
+      </LeaveToHomeProvider>
     );
   };
 
@@ -195,15 +205,14 @@ describe("Rageshake button", () => {
     };
 
     render(
-      <BrowserRouter>
+      <LeaveToHomeProvider value={leaveToHome}>
         <GroupCallErrorBoundary
           onError={vi.fn()}
           recoveryActionHandler={vi.fn()}
-          widget={null}
         >
           <TestComponent />
         </GroupCallErrorBoundary>
-      </BrowserRouter>,
+      </LeaveToHomeProvider>,
     );
   }
 
@@ -224,30 +233,28 @@ describe("Rageshake button", () => {
   });
 });
 
-test("should have a close button in widget mode", async () => {
+test("should have a close button when the host can dismiss us", async () => {
   const error = new MatrixRTCTransportMissingError("example.com");
   const TestComponent = (): ReactNode => {
     throw error;
   };
 
-  const mockWidget = {
-    api: {
-      transport: { send: vi.fn().mockResolvedValue(undefined), stop: vi.fn() },
-    },
-  } as unknown as WidgetHelpers;
+  const close = vi.fn().mockResolvedValue(undefined);
+  const hostBridge: HostBridge = { ...nullHostBridge, close };
 
   const user = userEvent.setup();
   const onErrorMock = vi.fn();
   const { asFragment } = render(
-    <BrowserRouter>
-      <GroupCallErrorBoundary
-        widget={mockWidget}
-        onError={onErrorMock}
-        recoveryActionHandler={vi.fn()}
-      >
-        <TestComponent />
-      </GroupCallErrorBoundary>
-    </BrowserRouter>,
+    <LeaveToHomeProvider value={leaveToHome}>
+      <HostBridgeProvider value={hostBridge}>
+        <GroupCallErrorBoundary
+          onError={onErrorMock}
+          recoveryActionHandler={vi.fn()}
+        >
+          <TestComponent />
+        </GroupCallErrorBoundary>
+      </HostBridgeProvider>
+    </LeaveToHomeProvider>,
   );
 
   await screen.findByText("Call is not supported");
@@ -258,11 +265,7 @@ test("should have a close button in widget mode", async () => {
 
   await user.click(screen.getByRole("button", { name: "Close" }));
 
-  expect(mockWidget.api.transport.send).toHaveBeenCalledWith(
-    ElementWidgetActions.Close,
-    expect.anything(),
-  );
-  expect(mockWidget.api.transport.stop).toHaveBeenCalled();
+  expect(close).toHaveBeenCalled();
 });
 
 test("should show technical details when error has a matrixError cause", async () => {
@@ -281,15 +284,11 @@ test("should show technical details when error has a matrixError cause", async (
   };
 
   render(
-    <BrowserRouter>
-      <GroupCallErrorBoundary
-        onError={vi.fn()}
-        recoveryActionHandler={vi.fn()}
-        widget={null}
-      >
+    <LeaveToHomeProvider value={leaveToHome}>
+      <GroupCallErrorBoundary onError={vi.fn()} recoveryActionHandler={vi.fn()}>
         <TestComponent />
       </GroupCallErrorBoundary>
-    </BrowserRouter>,
+    </LeaveToHomeProvider>,
   );
 
   await screen.findByText("Something went wrong");
@@ -314,15 +313,11 @@ test("should not show technical details when error has no matrix error cause", a
   };
 
   render(
-    <BrowserRouter>
-      <GroupCallErrorBoundary
-        onError={vi.fn()}
-        recoveryActionHandler={vi.fn()}
-        widget={null}
-      >
+    <LeaveToHomeProvider value={leaveToHome}>
+      <GroupCallErrorBoundary onError={vi.fn()} recoveryActionHandler={vi.fn()}>
         <TestComponent />
       </GroupCallErrorBoundary>
-    </BrowserRouter>,
+    </LeaveToHomeProvider>,
   );
 
   await screen.findByText("Connection lost");
@@ -372,15 +367,14 @@ describe("LiveKit ConnectionError variants", () => {
       };
 
       const { asFragment } = render(
-        <BrowserRouter>
+        <LeaveToHomeProvider value={leaveToHome}>
           <GroupCallErrorBoundary
             onError={vi.fn()}
             recoveryActionHandler={vi.fn()}
-            widget={null}
           >
             <TestComponent />
           </GroupCallErrorBoundary>
-        </BrowserRouter>,
+        </LeaveToHomeProvider>,
       );
 
       // Check title
@@ -402,15 +396,14 @@ describe("LiveKit ConnectionError variants", () => {
     };
 
     const { asFragment } = render(
-      <BrowserRouter>
+      <LeaveToHomeProvider value={leaveToHome}>
         <GroupCallErrorBoundary
           onError={vi.fn()}
           recoveryActionHandler={vi.fn()}
-          widget={null}
         >
           <TestComponent />
         </GroupCallErrorBoundary>
-      </BrowserRouter>,
+      </LeaveToHomeProvider>,
     );
 
     await screen.findByText("Connection timeout");
diff --git a/src/room/GroupCallErrorBoundary.tsx b/src/room/GroupCallErrorBoundary.tsx
index 390a5a8c2..6d43cf78f 100644
--- a/src/room/GroupCallErrorBoundary.tsx
+++ b/src/room/GroupCallErrorBoundary.tsx
@@ -34,7 +34,6 @@ import {
 } from "../utils/errors.ts";
 import { FullScreenView } from "../FullScreenView.tsx";
 import { ErrorView } from "../ErrorView.tsx";
-import { type WidgetHelpers } from "../widget.ts";
 import styles from "../ErrorView.module.css";
 
 export type CallErrorRecoveryAction = "reconnect"; // | "retry" ;
@@ -47,13 +46,11 @@ interface ErrorPageProps {
   error: ElementCallError;
   recoveryActionHandler: RecoveryActionHandler;
   resetError: () => void;
-  widget: WidgetHelpers | null;
 }
 
 const ErrorPage: FC<ErrorPageProps> = ({
   error,
   recoveryActionHandler,
-  widget,
 }: ErrorPageProps): ReactElement => {
   const { t } = useTranslation();
   logger.error("Error boundary caught:", error);
@@ -89,7 +86,6 @@ const ErrorPage: FC<ErrorPageProps> = ({
         Icon={icon}
         title={error.localisedTitle}
         rageshake={error.code == ErrorCode.UNKNOWN_ERROR}
-        widget={widget}
       >
         <p>
           {error.localisedMessageKey ? (
@@ -148,14 +144,12 @@ interface BoundaryProps {
   children: ReactNode | (() => ReactNode);
   recoveryActionHandler: RecoveryActionHandler;
   onError?: (error: unknown) => void;
-  widget: WidgetHelpers | null;
 }
 
 export const GroupCallErrorBoundary = ({
   recoveryActionHandler,
   onError,
   children,
-  widget,
 }: BoundaryProps): ReactElement => {
   const fallbackRenderer: FallbackRender = useCallback(
     ({ error, resetError }): ReactElement => {
@@ -165,7 +159,6 @@ export const GroupCallErrorBoundary = ({
           : new UnknownCallError(error instanceof Error ? error : new Error());
       return (
         <ErrorPage
-          widget={widget ?? null}
           error={callError}
           resetError={resetError}
           recoveryActionHandler={async (action: CallErrorRecoveryAction) => {
@@ -175,7 +168,7 @@ export const GroupCallErrorBoundary = ({
         />
       );
     },
-    [recoveryActionHandler, widget],
+    [recoveryActionHandler],
   );
 
   return (
diff --git a/src/room/InCallView.module.css b/src/room/InCallView.module.css
index 736a915a2..3c393cd6d 100644
--- a/src/room/InCallView.module.css
+++ b/src/room/InCallView.module.css
@@ -75,7 +75,7 @@ spotlight tile is maximised and displaying video, apply a gradient background. *
   background: none;
 }
 
-@media (max-width: 320px) {
+@container element-call (max-width: 320px) {
   .invite {
     display: none;
   }
diff --git a/src/room/InCallView.test.tsx b/src/room/InCallView.test.tsx
index 3113c0727..357bc186e 100644
--- a/src/room/InCallView.test.tsx
+++ b/src/room/InCallView.test.tsx
@@ -14,7 +14,7 @@ import {
   type MockedFunction,
   vi,
 } from "vitest";
-import { render, type RenderResult } from "@testing-library/react";
+import { act, render, type RenderResult } from "@testing-library/react";
 import { type LocalParticipant } from "livekit-client";
 import { BehaviorSubject, of } from "rxjs";
 import { BrowserRouter } from "react-router-dom";
@@ -51,6 +51,7 @@ import { AppBar } from "../AppBar";
 import { type MatrixInfo } from "./VideoPreview";
 import { ProcessorProvider } from "../livekit/TrackProcessorContext";
 import { initializeWidget } from "../widget";
+import { RootElementProvider } from "../RootElementContext";
 
 initializeWidget();
 vi.hoisted(
@@ -263,4 +264,71 @@ describe("ActiveCall", () => {
     // Rendering at all proves ActiveCall created all of its view models
     expect(await findByTestId("incall_leave")).toBeVisible();
   });
+
+  it("lays the call out for the size of its root element", async () => {
+    // jsdom has no layout and no ResizeObserver: the root reports whatever
+    // size we say, and the observer notifies whenever we tell it to
+    let size = { width: 1000, height: 800 };
+    const root = document.createElement("div");
+    Object.defineProperty(root, "clientWidth", { get: () => size.width });
+    Object.defineProperty(root, "clientHeight", { get: () => size.height });
+    document.body.appendChild(root);
+
+    const observers: (() => void)[] = [];
+    const originalResizeObserver = window.ResizeObserver;
+    window.ResizeObserver = class {
+      public constructor(private readonly callback: ResizeObserverCallback) {}
+      public observe(): void {
+        observers.push(() => this.callback([], this as ResizeObserver));
+      }
+      public unobserve(): void {}
+      public disconnect(): void {}
+    } as unknown as typeof ResizeObserver;
+
+    try {
+      const mediaDevices = mockMediaDevices({});
+      const { rtcSession, matrixRoom } = getBasicRTCSession([local, alice]);
+      const { findByTestId, container } = render(
+        <BrowserRouter>
+          <RootElementProvider value={root}>
+            <MediaDevicesContext value={mediaDevices}>
+              <ProcessorProvider>
+                <TooltipProvider>
+                  <RoomContext value={mockLivekitRoom({ localParticipant })}>
+                    <ActiveCall
+                      client={matrixRoom.client}
+                      rtcSession={rtcSession.asMockedSession()}
+                      matrixRoom={matrixRoom}
+                      muteStates={mockMuteStates()}
+                      matrixInfo={matrixInfo}
+                      onShareClick={null}
+                      e2eeSystem={{ kind: E2eeType.NONE }}
+                      onLeft={(): void => {}}
+                    />
+                  </RoomContext>
+                </TooltipProvider>
+              </ProcessorProvider>
+            </MediaDevicesContext>
+          </RootElementProvider>
+        </BrowserRouter>,
+        { container: root },
+      );
+      await findByTestId("incall_leave");
+      const call = container.querySelector("[data-layout]")!;
+      expect(call.getAttribute("data-layout")).not.toBe("pip");
+
+      // The host shrinks the container to a corner of its page. The window has
+      // not changed at all — what matters is the element we were given.
+      size = { width: 300, height: 300 };
+      act(() => observers.forEach((notify) => notify()));
+      expect(call.getAttribute("data-layout")).toBe("pip");
+
+      size = { width: 1000, height: 800 };
+      act(() => observers.forEach((notify) => notify()));
+      expect(call.getAttribute("data-layout")).not.toBe("pip");
+    } finally {
+      window.ResizeObserver = originalResizeObserver;
+      root.remove();
+    }
+  });
 });
diff --git a/src/room/InCallView.tsx b/src/room/InCallView.tsx
index 85fe66a74..5f706cabd 100644
--- a/src/room/InCallView.tsx
+++ b/src/room/InCallView.tsx
@@ -28,7 +28,9 @@ import { useTranslation } from "react-i18next";
 import { Header, LeftNav, RightNav, RoomHeaderInfo } from "../Header";
 import { HeaderStyle, useUrlParams } from "../UrlParams";
 import { useCallViewKeyboardShortcuts } from "../useCallViewKeyboardShortcuts";
-import { widget } from "../widget";
+import { useHostBridge } from "../HostBridge.ts";
+import { useRootElement } from "../RootElementContext";
+import { observeElementSize$ } from "../utils/elementSize";
 import styles from "./InCallView.module.css";
 import { GridTile } from "../tile/GridTile";
 import { SettingsModal, defaultSettingsTab } from "../settings/SettingsModal";
@@ -41,6 +43,7 @@ import { type MatrixInfo } from "./VideoPreview";
 import { InviteButton } from "../button/InviteButton";
 import {
   type CallViewModel,
+  callViewModelOptionsFromParams,
   createCallViewModel$,
 } from "../state/CallViewModel/CallViewModel.ts";
 import { Grid, type TileProps } from "../grid/Grid";
@@ -116,8 +119,12 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
     useState<ViewModel<DeveloperSettingsSnapshot> | null>(null);
 
   const urlParams = useUrlParams();
+  const hostBridge = useHostBridge();
   const mediaDevices = useMediaDevices();
   const trackProcessorState$ = useTrackProcessorObservable$();
+  // The element we have to draw the call in: the page, or the container a host
+  // gave us. Its size, not the window's, decides how the call is laid out.
+  const rootElement = useRootElement();
   useEffect(() => {
     rootLogger.info("START CALL VIEW SCOPE");
     const scope = new ObservableScope();
@@ -132,12 +139,15 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
       mediaDevices,
       props.muteStates,
       {
+        ...callViewModelOptionsFromParams(urlParams),
         encryptionSystem: props.e2eeSystem,
+        hostBridge,
         autoLeaveWhenOthersLeft,
         waitForCallPickup: waitForCallPickup && sendNotificationType === "ring",
         // We merely sample the current mode here, so the user would need to
         // manually rejoin to switch to a different one.
         matrixRTCMode: matrixRTCModeSetting.value$.value,
+        windowSize$: scope.behavior(observeElementSize$(rootElement)),
       },
       reactionsReader.raisedHands$,
       reactionsReader.reactions$,
@@ -159,9 +169,11 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
     props.e2eeSystem,
     props.onLeft,
     urlParams,
+    hostBridge,
     mediaDevices,
     trackProcessorState$,
     props.client,
+    rootElement,
   ]);
 
   useEffect(() => {
@@ -174,6 +186,7 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
       props.muteStates,
       mediaDevices,
       `${props.client.getUserId()}:${props.client.getDeviceId()}`,
+      { showControls: urlParams.showControls, header: urlParams.header },
     );
     setFooterVm(footerVm);
     setDeveloperSettingsVm(createDeveloperSettingsTabViewModel(scope, vm));
@@ -234,6 +247,7 @@ export const InCallView: FC<InCallViewProps> = ({
 }) => {
   const logger = rootLogger.getChild("[InCallView]");
   const { t } = useTranslation();
+  const hostBridge = useHostBridge();
   const { sendReaction, toggleRaisedHand } = useReactionsSender();
 
   useWakeLock();
@@ -253,6 +267,20 @@ export const InCallView: FC<InCallViewProps> = ({
   // Merge the refs so they can attach to the same element
   const containerRef = useMergedRefs(containerRef1, containerRef2);
 
+  // The fixed grid is positioned against Element Call's root, so offsets
+  // handed to it have to be measured from there rather than from the
+  // viewport. Standalone the two are the same, the root being the page; for a
+  // component the root sits wherever the host put it, and measuring from the
+  // viewport would push the grid down by that much again. Taken at the same
+  // moment as `bounds`, so that the two agree however the host has scrolled.
+  const rootElement = useRootElement();
+  const rootTop = useMemo(
+    () => rootElement.getBoundingClientRect().top,
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [rootElement, bounds],
+  );
+  const topWithinRoot = bounds.top - rootTop;
+
   const { showControls, header: headerStyle } = useUrlParams();
 
   const muteAllAudio = useBehavior(muteAllAudio$);
@@ -318,14 +346,14 @@ export const InCallView: FC<InCallViewProps> = ({
 
   const openProfile = useMemo(
     () =>
-      // Profile settings are unavailable in widget mode
-      widget === null
+      // The profile is only ours to edit when the account is ours
+      hostBridge.supportsProfileChanges
         ? (): void => {
             setSettingsTab("profile");
             setSettingsOpen(true);
           }
         : null,
-    [setSettingsTab, setSettingsOpen],
+    [setSettingsTab, setSettingsOpen, hostBridge],
   );
 
   const [headerRef, headerBounds] = useMeasure();
@@ -550,7 +578,7 @@ export const InCallView: FC<InCallViewProps> = ({
         className={styles.fixedGrid}
         style={{
           // If not edge-to-edge, consume the header insets right here.
-          insetBlockStart: edgeToEdge ? 0 : bounds.top + headerBounds.height,
+          insetBlockStart: edgeToEdge ? 0 : topWithinRoot + headerBounds.height,
           height: edgeToEdge ? "100%" : gridBounds.height,
           // If edge-to-edge, compute new safe area insets that account for the
           // header and footer, passing them down to the tiles.
@@ -561,7 +589,7 @@ export const InCallView: FC<InCallViewProps> = ({
                 // itself. Otherwise account for the safe area and header size
                 // as part of the InCallView.
                 headerStyle === HeaderStyle.AppBar
-                ? `${bounds.top}px`
+                ? `${topWithinRoot}px`
                 : `calc(env(safe-area-inset-top) + ${headerBounds.height}px)`
               : undefined,
           "--call-view-safe-area-inset-bottom":
@@ -633,6 +661,9 @@ export const InCallView: FC<InCallViewProps> = ({
         [styles.overflowing]: overflowing,
       })}
       ref={containerRef}
+      // Which layout the call has settled on, for tests and for anyone
+      // wondering why the call looks the way it does at the size it was given
+      data-layout={layout.type}
       onPointerUp={onViewPointerUp}
       onPointerMove={onPointerMove}
       onPointerOut={onPointerOut}
diff --git a/src/room/KnockLobbyView.test.tsx b/src/room/KnockLobbyView.test.tsx
new file mode 100644
index 000000000..a513952b7
--- /dev/null
+++ b/src/room/KnockLobbyView.test.tsx
@@ -0,0 +1,95 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, it, vi } from "vitest";
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { TooltipProvider } from "@vector-im/compound-web";
+import { type MatrixClient, type RoomSummary } from "matrix-js-sdk";
+
+import { KnockLobbyView } from "./KnockLobbyView";
+import { LeaveToHomeProvider } from "../LeaveToHomeContext";
+import { MediaDevicesContext } from "../MediaDevicesContext";
+import { type ProcessorState } from "../livekit/TrackProcessorContext";
+import { mockMediaDevices } from "../utils/test";
+
+vi.mock("@livekit/components-react", () => ({
+  usePreviewTracks: (): unknown[] => [],
+}));
+
+vi.mock("../livekit/TrackProcessorContext", () => ({
+  useTrackProcessor: (): ProcessorState => ({
+    supported: false,
+    processor: undefined,
+  }),
+  useTrackProcessorSync: (): void => {},
+}));
+
+vi.mock("react-use-measure", () => ({
+  default: (): [() => void, object] => [(): void => {}, {}],
+}));
+
+vi.mock("../settings/SettingsModal", () => ({
+  SettingsModal: (): null => null,
+  defaultSettingsTab: "general",
+}));
+
+const client = {
+  getUserId: () => "@user:example.org",
+  getDeviceId: () => "DEVICE",
+} as Partial<MatrixClient> as MatrixClient;
+
+// What peeking at a room we are not in tells us about it
+const roomSummary = {
+  room_id: "!room:example.org",
+  name: "Knock Room",
+  "im.nheko.summary.encryption": "m.megolm.v1.aes-sha2",
+} as Partial<RoomSummary> as RoomSummary;
+
+function renderKnockLobby(knock: (() => void) | null): void {
+  render(
+    <LeaveToHomeProvider value={vi.fn()}>
+      <MediaDevicesContext value={mockMediaDevices({})}>
+        <TooltipProvider>
+          <KnockLobbyView
+            client={client}
+            roomSummary={roomSummary}
+            profile={{ displayName: "Test User", avatarUrl: "" }}
+            knock={knock}
+            confineToRoom={false}
+            hideHeader={false}
+          />
+        </TooltipProvider>
+      </MediaDevicesContext>
+    </LeaveToHomeProvider>,
+  );
+}
+
+describe("KnockLobbyView", () => {
+  it("offers to ask to join, with what it knows of the room", async () => {
+    const knock = vi.fn();
+    renderKnockLobby(knock);
+
+    // The mute state arrives asynchronously, and the lobby with it
+    const button = await screen.findByTestId("lobby_joinCall");
+    expect(button).toHaveTextContent("Request to join call");
+    expect(button).toBeEnabled();
+    expect(screen.getByText("Knock Room")).toBeInTheDocument();
+
+    await userEvent.setup().click(button);
+    expect(knock).toHaveBeenCalledOnce();
+  });
+
+  it("waits once it has asked", async () => {
+    renderKnockLobby(null);
+
+    const button = await screen.findByTestId("lobby_joinCall");
+    expect(button).toHaveTextContent("Request sent!");
+    // Compound's button keeps focusable, saying so through ARIA instead
+    expect(button).toHaveAttribute("aria-disabled", "true");
+  });
+});
diff --git a/src/room/KnockLobbyView.tsx b/src/room/KnockLobbyView.tsx
new file mode 100644
index 000000000..39643b20c
--- /dev/null
+++ b/src/room/KnockLobbyView.tsx
@@ -0,0 +1,92 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type FC, type JSX, type ReactNode } from "react";
+import { type MatrixClient, type RoomSummary } from "matrix-js-sdk";
+import { useTranslation } from "react-i18next";
+import { CheckIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
+
+import { LobbyView } from "./LobbyView";
+import { E2eeType } from "../e2ee/e2eeType";
+import { useMuteStates } from "../state/useMuteStates";
+
+interface Props {
+  client: MatrixClient;
+  /** What we know about the room from peeking at it. */
+  roomSummary: RoomSummary;
+  /** The user's own name and avatar, to show in their own tile. */
+  profile: { displayName: string; avatarUrl: string };
+  /**
+   * Asks to be let in, if the room allows it. Absent once we have asked and
+   * are waiting for an answer.
+   */
+  knock: (() => void) | null;
+  confineToRoom: boolean;
+  hideHeader: boolean;
+}
+
+/**
+ * The lobby shown while the user is outside a room they want to call in —
+ * either able to ask to join, or waiting for someone to answer.
+ *
+ * This belongs to the app shell rather than to the call: it exists precisely
+ * because there is no call to be in yet. It keeps its own mute state, which is
+ * why it is a component rather than part of the page — so that the call's mute
+ * state and this one are never alive at the same time, reporting over each
+ * other to the host.
+ */
+export const KnockLobbyView: FC<Props> = ({
+  client,
+  roomSummary,
+  profile,
+  knock,
+  confineToRoom,
+  hideHeader,
+}): ReactNode => {
+  const { t } = useTranslation();
+  const muteStates = useMuteStates();
+
+  if (muteStates === null) return null;
+
+  const waitingForInvite = knock === null;
+  const enterLabel: string | JSX.Element = waitingForInvite ? (
+    <>
+      {t("lobby.waiting_for_invite")}
+      <CheckIcon />
+    </>
+  ) : (
+    t("lobby.ask_to_join")
+  );
+
+  return (
+    <LobbyView
+      client={client}
+      matrixInfo={{
+        userId: client.getUserId() ?? "",
+        displayName: profile.displayName,
+        avatarUrl: profile.avatarUrl,
+        roomAlias: null,
+        roomId: roomSummary.room_id,
+        roomName: roomSummary.name ?? "",
+        roomAvatar: roomSummary.avatar_url ?? null,
+        e2eeSystem: {
+          kind: roomSummary["im.nheko.summary.encryption"]
+            ? E2eeType.PER_PARTICIPANT
+            : E2eeType.NONE,
+        },
+      }}
+      onEnter={(): void => knock?.()}
+      enterLabel={enterLabel}
+      waitingForInvite={waitingForInvite}
+      confineToRoom={confineToRoom}
+      hideHeader={hideHeader}
+      participantCount={null}
+      muteStates={muteStates}
+      onShareClick={null}
+    />
+  );
+};
diff --git a/src/room/LobbyView.module.css b/src/room/LobbyView.module.css
index b66d483cc..b112cdf20 100644
--- a/src/room/LobbyView.module.css
+++ b/src/room/LobbyView.module.css
@@ -28,13 +28,13 @@ Please see LICENSE in the repository root for full details.
   color: var(--cpd-color-theme-primary) !important;
 }
 
-@media (max-width: 500px) {
+@container element-call (max-width: 500px) {
   .join {
     width: 100%;
   }
 }
 
-@media (min-height: 650px) {
+@container element-call (min-height: 650px) {
   .content {
     gap: var(--cpd-space-10x);
   }
diff --git a/src/room/LobbyView.test.tsx b/src/room/LobbyView.test.tsx
index 8cbe6be14..7f03f2d29 100644
--- a/src/room/LobbyView.test.tsx
+++ b/src/room/LobbyView.test.tsx
@@ -7,7 +7,7 @@ Please see LICENSE in the repository root for full details.
 
 import { describe, expect, it, vi } from "vitest";
 import { render } from "@testing-library/react";
-import { BrowserRouter } from "react-router-dom";
+import { LeaveToHomeProvider } from "../LeaveToHomeContext";
 import { TooltipProvider } from "@vector-im/compound-web";
 import { type MatrixClient } from "matrix-js-sdk";
 import { axe } from "vitest-axe";
@@ -26,6 +26,9 @@ import lobbyStyles from "./LobbyView.module.css";
 import headerStyles from "../Header.module.css";
 import { AppBar } from "../AppBar";
 
+// Somewhere to go home to, so that the lobby offers the way back
+const leaveToHome = vi.fn();
+
 vi.mock("@livekit/components-react", () => ({
   usePreviewTracks: (): unknown[] => [],
 }));
@@ -93,14 +96,14 @@ function renderLobbyView(
     />
   );
   return render(
-    <BrowserRouter>
+    <LeaveToHomeProvider value={leaveToHome}>
       <MediaDevicesContext value={mediaDevices}>
         <TooltipProvider>
           {withAppBar && <AppBar>{lobbyView}</AppBar>}
           {!withAppBar && lobbyView}
         </TooltipProvider>
       </MediaDevicesContext>
-    </BrowserRouter>,
+    </LeaveToHomeProvider>,
   );
 }
 
diff --git a/src/room/LobbyView.tsx b/src/room/LobbyView.tsx
index e122b3f26..9e6e0ed99 100644
--- a/src/room/LobbyView.tsx
+++ b/src/room/LobbyView.tsx
@@ -25,7 +25,6 @@ import {
   Track,
 } from "livekit-client";
 import { useObservableEagerState } from "observable-hooks";
-import { useNavigate } from "react-router-dom";
 
 import inCallStyles from "./InCallView.module.css";
 import styles from "./LobbyView.module.css";
@@ -34,9 +33,10 @@ import { type MatrixInfo, VideoPreview } from "./VideoPreview";
 import { type MuteStates } from "../state/MuteStates";
 import { InviteButton } from "../button/InviteButton";
 import { SettingsModal, defaultSettingsTab } from "../settings/SettingsModal";
-import { useMediaQuery } from "../useMediaQuery";
+import { useRootSizeMatches } from "../useRootSize";
 import { E2eeType } from "../e2ee/e2eeType";
-import { Link } from "../button/Link";
+import { LeaveToHomeLink } from "../button/LeaveToHomeLink";
+import { useLeaveToHome } from "../LeaveToHomeContext";
 import { useMediaDevices } from "../MediaDevicesContext";
 import { ObservableScope } from "../state/ObservableScope";
 import { useInitial } from "../useInitial";
@@ -44,7 +44,6 @@ import {
   useTrackProcessor,
   useTrackProcessorSync,
 } from "../livekit/TrackProcessorContext";
-import { usePageTitle } from "../usePageTitle";
 import { getValue } from "../utils/observable";
 import { useBehavior } from "../useBehavior";
 import { CallFooter, type FooterSnapshot } from "../components/CallFooter";
@@ -87,7 +86,6 @@ export const LobbyView: FC<Props> = ({
 
   const { t } = useTranslation();
 
-  usePageTitle(matrixInfo.roomName);
   useAppBarPrimaryButtonIconKind("back");
   const audioEnabled = useBehavior(muteStates.audio.enabled$);
   const videoEnabled = useBehavior(muteStates.video.enabled$);
@@ -111,19 +109,19 @@ export const LobbyView: FC<Props> = ({
     [setSettingsModalOpen],
   );
 
-  const navigate = useNavigate();
-  const onLeaveClick = useCallback(() => {
-    navigate("/")?.catch((error) => {
-      logger.error("Failed to navigate to /", error);
-    });
-  }, [navigate]);
-  const hangup = confineToRoom ? undefined : onLeaveClick;
+  // Leaving the lobby means going back to wherever the user came from, if
+  // there is such a place
+  const leaveToHome = useLeaveToHome();
+  const hangup =
+    confineToRoom || leaveToHome === null ? undefined : leaveToHome;
 
-  const recentsButtonInFooter = useMediaQuery("(max-height: 500px)");
+  const recentsButtonInFooter = useRootSizeMatches(
+    ({ height }) => height <= 500,
+  );
   const recentsButton = !confineToRoom && (
-    <Link className={styles.recents} to="/">
+    <LeaveToHomeLink className={styles.recents}>
       {t("lobby.leave_button")}
-    </Link>
+    </LeaveToHomeLink>
   );
 
   const devices = useMediaDevices();
@@ -209,7 +207,7 @@ export const LobbyView: FC<Props> = ({
     return (): void => {
       footerScope.end();
     };
-  }, [devices, hangup, hideHeader, muteStates, onLeaveClick, openSettings]);
+  }, [devices, hangup, hideHeader, muteStates, openSettings]);
 
   // TODO: Unify this component with InCallView, so we can get slick joining
   // animations and don't have to feel bad about reusing its CSS
diff --git a/src/room/ReactionsOverlay.module.css b/src/room/ReactionsOverlay.module.css
index 3738dc09e..618adbf38 100644
--- a/src/room/ReactionsOverlay.module.css
+++ b/src/room/ReactionsOverlay.module.css
@@ -3,8 +3,11 @@
   display: inline;
   z-index: 2;
   pointer-events: none;
-  width: 100vw;
-  height: 100vh;
+  /* Percentages, not viewport units: the containing block is the element
+  Element Call treats as its root, which is the page in the standalone app but
+  the container a host gave us when embedded. */
+  width: 100%;
+  height: 100%;
   left: 0;
   top: 0;
 }
@@ -16,7 +19,7 @@
   animation-name: reaction-up;
   width: fit-content;
   position: relative;
-  top: 80vh;
+  top: 80%;
 }
 
 @keyframes reaction-up {
@@ -24,7 +27,7 @@
     opacity: 1;
     translate: 0 0;
     scale: 200%;
-    top: 80vh;
+    top: 80%;
   }
 
   to {
@@ -48,7 +51,7 @@
   .reaction {
     font-size: 48pt;
     animation-name: reaction-up-reduced;
-    top: calc(-50vh + (48pt / 2));
-    left: calc(50vw - (48pt / 2)) !important;
+    top: calc(-50% + (48pt / 2));
+    left: calc(50% - (48pt / 2)) !important;
   }
 }
diff --git a/src/room/RoomPage.tsx b/src/room/RoomPage.tsx
index b1ffb3ba2..71bceea76 100644
--- a/src/room/RoomPage.tsx
+++ b/src/room/RoomPage.tsx
@@ -6,41 +6,27 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import {
-  type FC,
-  useEffect,
-  useState,
-  type ReactNode,
-  useRef,
-  type JSX,
-} from "react";
+import { type FC, useEffect, useState, type ReactNode, useRef } from "react";
 import { type MatrixError } from "matrix-js-sdk";
 import { logger } from "matrix-js-sdk/lib/logger";
 import { Trans, useTranslation } from "react-i18next";
-import {
-  CheckIcon,
-  UnknownSolidIcon,
-} from "@vector-im/compound-design-tokens/assets/web/icons";
+import { UnknownSolidIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
 
 import { useClientLegacy } from "../ClientContext";
 import { ErrorPage, FullScreenView, LoadingPage } from "../FullScreenView";
 import { RoomAuthView } from "./RoomAuthView";
-import { GroupCallView } from "./GroupCallView";
+import { CallView } from "./CallView";
 import { useRoomIdentifier, useUrlParams } from "../UrlParams";
 import { useRegisterPasswordlessUser } from "../auth/useRegisterPasswordlessUser";
 import { HomePage } from "../home/HomePage";
-import { widget } from "../widget";
 import { CallTerminatedMessage, useLoadGroupCall } from "./useLoadGroupCall";
-import { LobbyView } from "./LobbyView";
-import { E2eeType } from "../e2ee/e2eeType";
+import { KnockLobbyView } from "./KnockLobbyView";
 import { useProfile } from "../profile/useProfile";
 import { useOptInAnalytics } from "../settings/settings";
 import { Link } from "../button/Link";
 import { ErrorView } from "../ErrorView";
-import { useMediaDevices } from "../MediaDevicesContext";
-import { MuteStates } from "../state/MuteStates";
-import { ObservableScope } from "../state/ObservableScope";
-import { calculateInitialMuteState } from "../state/initialMuteState.ts";
+import { usePageTitle } from "../usePageTitle";
+import { useRoomName } from "./useRoomName";
 
 export const RoomPage: FC = (): ReactNode => {
   const urlParams = useUrlParams();
@@ -61,31 +47,25 @@ export const RoomPage: FC = (): ReactNode => {
   const { avatarUrl, displayName: userDisplayName } = useProfile(client);
 
   const groupCallState = useLoadGroupCall(client, roomIdOrAlias, viaServers);
-  const [joined, setJoined] = useState(false);
 
-  const devices = useMediaDevices();
-  const [muteStates, setMuteStates] = useState<MuteStates | null>(null);
-
-  useEffect(() => {
-    const scope = new ObservableScope();
-    setMuteStates(
-      new MuteStates(
-        scope,
-        devices,
-        calculateInitialMuteState(
-          urlParams.skipLobby,
-          urlParams.callIntent,
-          widget !== null,
-        ),
-      ),
-    );
-    return (): void => scope.end();
-  }, [devices, urlParams]);
+  // The page title is the page's to set, not the call's: a host embedding the
+  // call has a title of its own. So it is set here, for whichever room we have
+  // got as far as knowing about.
+  const roomName = useRoomName(
+    groupCallState.kind === "loaded" ? groupCallState.rtcSession.room : null,
+  );
+  usePageTitle(
+    roomName ??
+      (groupCallState.kind === "canKnock" ||
+      groupCallState.kind === "waitForInvite"
+        ? groupCallState.roomSummary.name
+        : undefined),
+  );
 
   useEffect(() => {
     // If we've finished loading, are not already authed and we've been given a display name as
     // a URL param, automatically register a passwordless user
-    if (!loading && !authenticated && displayName && !widget) {
+    if (!loading && !authenticated && displayName && !urlParams.isWidget) {
       setIsRegistering(true);
       registerPasswordlessUser(displayName)
         .catch((e) => {
@@ -99,6 +79,7 @@ export const RoomPage: FC = (): ReactNode => {
     loading,
     authenticated,
     displayName,
+    urlParams.isWidget,
     setIsRegistering,
     registerPasswordlessUser,
   ]);
@@ -121,67 +102,34 @@ export const RoomPage: FC = (): ReactNode => {
     switch (groupCallState.kind) {
       case "loaded":
         return (
-          muteStates && (
-            <GroupCallView
-              widget={widget}
-              client={client!}
-              rtcSession={groupCallState.rtcSession}
-              joined={joined}
-              setJoined={setJoined}
-              isPasswordlessUser={passwordlessUser}
-              confineToRoom={confineToRoom}
-              preload={preload}
-              skipLobby={skipLobby || wasInWaitForInviteState.current}
-              muteStates={muteStates}
-            />
-          )
+          <CallView
+            client={client!}
+            rtcSession={groupCallState.rtcSession}
+            isPasswordlessUser={passwordlessUser}
+            confineToRoom={confineToRoom}
+            preload={preload}
+            skipLobby={skipLobby || wasInWaitForInviteState.current}
+          />
         );
       case "waitForInvite":
       case "canKnock": {
         wasInWaitForInviteState.current =
           wasInWaitForInviteState.current ||
           groupCallState.kind === "waitForInvite";
-        const knock =
-          groupCallState.kind === "canKnock" ? groupCallState.knock : null;
-        const label: string | JSX.Element =
-          groupCallState.kind === "canKnock" ? (
-            t("lobby.ask_to_join")
-          ) : (
-            <>
-              {t("lobby.waiting_for_invite")}
-              <CheckIcon />
-            </>
-          );
         return (
-          muteStates && (
-            <LobbyView
-              client={client!}
-              matrixInfo={{
-                userId: client!.getUserId() ?? "",
-                displayName: userDisplayName ?? "",
-                avatarUrl: avatarUrl ?? "",
-                roomAlias: null,
-                roomId: groupCallState.roomSummary.room_id,
-                roomName: groupCallState.roomSummary.name ?? "",
-                roomAvatar: groupCallState.roomSummary.avatar_url ?? null,
-                e2eeSystem: {
-                  kind: groupCallState.roomSummary[
-                    "im.nheko.summary.encryption"
-                  ]
-                    ? E2eeType.PER_PARTICIPANT
-                    : E2eeType.NONE,
-                },
-              }}
-              onEnter={(): void => knock?.()}
-              enterLabel={label}
-              waitingForInvite={groupCallState.kind === "waitForInvite"}
-              confineToRoom={confineToRoom}
-              hideHeader={header !== "standard"}
-              participantCount={null}
-              muteStates={muteStates}
-              onShareClick={null}
-            />
-          )
+          <KnockLobbyView
+            client={client!}
+            roomSummary={groupCallState.roomSummary}
+            profile={{
+              displayName: userDisplayName ?? "",
+              avatarUrl: avatarUrl ?? "",
+            }}
+            knock={
+              groupCallState.kind === "canKnock" ? groupCallState.knock : null
+            }
+            confineToRoom={confineToRoom}
+            hideHeader={header !== "standard"}
+          />
         );
       }
       case "loading":
@@ -198,7 +146,6 @@ export const RoomPage: FC = (): ReactNode => {
               <ErrorView
                 Icon={UnknownSolidIcon}
                 title={t("error.call_not_found")}
-                widget={widget}
               >
                 <Trans i18nKey="error.call_not_found_description">
                   <p>
@@ -216,7 +163,6 @@ export const RoomPage: FC = (): ReactNode => {
               <ErrorView
                 Icon={groupCallState.error.icon}
                 title={groupCallState.error.message}
-                widget={widget}
               >
                 <p>{groupCallState.error.messageBody}</p>
                 {groupCallState.error.reason && (
@@ -230,7 +176,7 @@ export const RoomPage: FC = (): ReactNode => {
             </FullScreenView>
           );
         } else {
-          return <ErrorPage widget={widget} error={groupCallState.error} />;
+          return <ErrorPage error={groupCallState.error} />;
         }
       default:
         return <> </>;
@@ -238,7 +184,7 @@ export const RoomPage: FC = (): ReactNode => {
   };
 
   if (loading || isRegistering) return <LoadingPage />;
-  if (error) return <ErrorPage widget={widget} error={error} />;
+  if (error) return <ErrorPage error={error} />;
   if (!client) return <RoomAuthView />;
   // TODO: This doesn't belong here, the app routes need to be reworked
   if (!roomIdOrAlias) return <HomePage />;
diff --git a/src/room/VideoPreview.module.css b/src/room/VideoPreview.module.css
index 67eae10bb..4d3d0562c 100644
--- a/src/room/VideoPreview.module.css
+++ b/src/room/VideoPreview.module.css
@@ -9,7 +9,9 @@ Please see LICENSE in the repository root for full details.
   margin-left: var(--content-inset-left);
   margin-right: var(--content-inset-right);
   min-block-size: 0;
-  block-size: 50vh;
+  /* Half the height of Element Call's root, not of the viewport: embedded,
+  the two differ (see the note on container units in base.css) */
+  block-size: 50cqh;
   aspect-ratio: 16 / 9;
   max-width: 100%;
   border-radius: var(--cpd-space-4x);
@@ -71,7 +73,7 @@ video.mirror {
   );
 }
 
-@media (max-width: 550px) {
+@container element-call (max-width: 550px) {
   .preview {
     margin-inline: 0;
     border-radius: 0;
diff --git a/src/room/__snapshots__/GroupCallErrorBoundary.test.tsx.snap b/src/room/__snapshots__/GroupCallErrorBoundary.test.tsx.snap
index 4239cee13..7a1fc0457 100644
--- a/src/room/__snapshots__/GroupCallErrorBoundary.test.tsx.snap
+++ b/src/room/__snapshots__/GroupCallErrorBoundary.test.tsx.snap
@@ -11,11 +11,10 @@ exports[`ConnectionLostError: Action handling should reset error state 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -92,7 +91,7 @@ exports[`ConnectionLostError: Action handling should reset error state 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -169,11 +168,10 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'internal' er
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -250,7 +248,7 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'internal' er
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -326,11 +324,10 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'notAllowed'
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -407,7 +404,7 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'notAllowed'
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -483,11 +480,10 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'serverUnreac
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -564,7 +560,7 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'serverUnreac
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -640,11 +636,10 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'serviceNotFo
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -721,7 +716,7 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'serviceNotFo
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -797,11 +792,10 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'timeout' err
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -878,7 +872,7 @@ exports[`LiveKit ConnectionError variants > should display LiveKit 'timeout' err
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -954,11 +948,10 @@ exports[`LiveKit ConnectionError variants > should link to troubleshoot guide wh
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1035,7 +1028,7 @@ exports[`LiveKit ConnectionError variants > should link to troubleshoot guide wh
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1100,7 +1093,7 @@ exports[`LiveKit ConnectionError variants > should link to troubleshoot guide wh
 </DocumentFragment>
 `;
 
-exports[`should have a close button in widget mode 1`] = `
+exports[`should have a close button when the host can dismiss us 1`] = `
 <DocumentFragment>
   <div
     class="_page_4be5c0"
@@ -1111,11 +1104,10 @@ exports[`should have a close button in widget mode 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1192,7 +1184,7 @@ exports[`should have a close button in widget mode 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1265,11 +1257,10 @@ exports[`should render the error page with link back to home 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1346,7 +1337,7 @@ exports[`should render the error page with link back to home 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1419,11 +1410,10 @@ exports[`should report correct error for 'Call is not supported' 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1500,7 +1490,7 @@ exports[`should report correct error for 'Call is not supported' 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1573,11 +1563,10 @@ exports[`should report correct error for 'Connection lost' 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1654,7 +1643,7 @@ exports[`should report correct error for 'Connection lost' 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1731,11 +1720,10 @@ exports[`should report correct error for 'Homeserver does not support Matrix 2.
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1812,7 +1800,7 @@ exports[`should report correct error for 'Homeserver does not support Matrix 2.
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -1885,11 +1873,10 @@ exports[`should report correct error for 'Incompatible browser' 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -1966,7 +1953,7 @@ exports[`should report correct error for 'Incompatible browser' 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
@@ -2034,11 +2021,10 @@ exports[`should report correct error for 'Insufficient capacity' 1`] = `
       <div
         class="_nav_e4b327 _leftNav_e4b327"
       >
-        <a
+        <button
           aria-label="Element Call Home"
           class="_headerLogo_e4b327"
-          data-discover="true"
-          href="/"
+          type="button"
         >
           <svg
             fill="none"
@@ -2115,7 +2101,7 @@ exports[`should report correct error for 'Insufficient capacity' 1`] = `
               fill="white"
             />
           </svg>
-        </a>
+        </button>
       </div>
       <div
         class="_nav_e4b327 _rightNav_e4b327"
diff --git a/src/room/__snapshots__/InCallView.test.tsx.snap b/src/room/__snapshots__/InCallView.test.tsx.snap
index 7cd044bfc..b7f8b3fe3 100644
--- a/src/room/__snapshots__/InCallView.test.tsx.snap
+++ b/src/room/__snapshots__/InCallView.test.tsx.snap
@@ -4,6 +4,7 @@ exports[`InCallView > rendering > renders 1`] = `
 <div>
   <div
     class="_inRoom_4e7ff8"
+    data-layout="one-on-one-desktop"
   >
     <header
       class="_header_e4b327 _header_4e7ff8"
diff --git a/src/room/__snapshots__/LobbyView.test.tsx.snap b/src/room/__snapshots__/LobbyView.test.tsx.snap
index f3352a6ec..d66d4a8fe 100644
--- a/src/room/__snapshots__/LobbyView.test.tsx.snap
+++ b/src/room/__snapshots__/LobbyView.test.tsx.snap
@@ -88,7 +88,7 @@ exports[`LobbyView > renders with AppBar android 1`] = `
         class="_link_13esb_8"
         data-kind="primary"
         data-size="md"
-        href="/"
+        href="#"
         rel="noreferrer noopener"
       >
         Back to recents
@@ -320,7 +320,7 @@ exports[`LobbyView > renders with AppBar ios 1`] = `
         class="_link_13esb_8"
         data-kind="primary"
         data-size="md"
-        href="/"
+        href="#"
         rel="noreferrer noopener"
       >
         Back to recents
@@ -598,7 +598,7 @@ exports[`LobbyView > renders with header and participant count 1`] = `
         class="_link_13esb_8"
         data-kind="primary"
         data-size="md"
-        href="/"
+        href="#"
         rel="noreferrer noopener"
       >
         Back to recents
diff --git a/src/room/useLoadGroupCall.ts b/src/room/useLoadGroupCall.ts
index 8a7617d85..42464bb24 100644
--- a/src/room/useLoadGroupCall.ts
+++ b/src/room/useLoadGroupCall.ts
@@ -34,7 +34,7 @@ import {
   EndCallIcon,
 } from "@vector-im/compound-design-tokens/assets/web/icons";
 
-import { widget } from "../widget";
+import { useUrlParams } from "../UrlParams";
 
 export type GroupCallLoaded = {
   kind: "loaded";
@@ -132,6 +132,7 @@ export const useLoadGroupCall = (
   const [state, setState] = useState<GroupCallStatus>({ kind: "loading" });
   const activeRoom = useRef<Room | undefined>(undefined);
   const { t } = useTranslation();
+  const { isWidget } = useUrlParams();
 
   const bannedError = useCallback(
     (): CallTerminatedMessage =>
@@ -249,7 +250,7 @@ export const useLoadGroupCall = (
           // room already joined so we are done here already.
           return room!;
         }
-        if (widget)
+        if (isWidget)
           // in widget mode we never should reach this point. (getRoom should return the room.)
           throw new Error(
             "Room not found. The widget-api did not pass over the relevant room events/information.",
@@ -373,6 +374,7 @@ export const useLoadGroupCall = (
   }, [
     bannedError,
     client,
+    isWidget,
     knockRejectError,
     removeNoticeError,
     roomIdOrAlias,
diff --git a/src/room/useRoomName.ts b/src/room/useRoomName.ts
index 838578570..f20b3b2a8 100644
--- a/src/room/useRoomName.ts
+++ b/src/room/useRoomName.ts
@@ -6,14 +6,27 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { type Room, RoomEvent } from "matrix-js-sdk";
-import { useCallback } from "react";
+import { useCallback, useSyncExternalStore } from "react";
 
-import { useTypedEventEmitterState } from "../useEvents";
-
-export function useRoomName(room: Room): string {
-  return useTypedEventEmitterState(
-    room,
-    RoomEvent.Name,
-    useCallback(() => room.name, [room]),
+/**
+ * The room's name, kept up to date. Null when there is no room yet, for a
+ * caller that only sometimes has one.
+ */
+export function useRoomName(room: Room): string;
+export function useRoomName(room: Room | null): string | null;
+export function useRoomName(room: Room | null): string | null {
+  const subscribe = useCallback(
+    (onChange: () => void) => {
+      if (room === null) return (): void => {};
+      room.on(RoomEvent.Name, onChange);
+      return (): void => {
+        room.off(RoomEvent.Name, onChange);
+      };
+    },
+    [room],
+  );
+  return useSyncExternalStore(
+    subscribe,
+    useCallback(() => room?.name ?? null, [room]),
   );
 }
diff --git a/src/settings/DeveloperSettingsTab.module.css b/src/settings/DeveloperSettingsTab.module.css
index 29f4211bc..369bec3b7 100644
--- a/src/settings/DeveloperSettingsTab.module.css
+++ b/src/settings/DeveloperSettingsTab.module.css
@@ -5,7 +5,7 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-pre {
+.pre {
   font-size: var(--font-size-micro);
 }
 
diff --git a/src/settings/DeveloperSettingsTab.tsx b/src/settings/DeveloperSettingsTab.tsx
index 25b3c81ce..ec5bf7b08 100644
--- a/src/settings/DeveloperSettingsTab.tsx
+++ b/src/settings/DeveloperSettingsTab.tsx
@@ -680,9 +680,9 @@ export const DeveloperSettingsTab: FC<Props> = ({
       <AudioProcessingSettings />
       <Separator />
       <p>{t("developer_mode.environment_variables")}</p>
-      <pre>{JSON.stringify(env, null, 2)}</pre>
+      <pre className={styles.pre}>{JSON.stringify(env, null, 2)}</pre>
       <p>{t("developer_mode.url_params")}</p>
-      <pre>{JSON.stringify(urlParams, null, 2)}</pre>
+      <pre className={styles.pre}>{JSON.stringify(urlParams, null, 2)}</pre>
     </>
   );
 };
diff --git a/src/settings/SettingsModal.tsx b/src/settings/SettingsModal.tsx
index b2ffef4ab..933ac66f5 100644
--- a/src/settings/SettingsModal.tsx
+++ b/src/settings/SettingsModal.tsx
@@ -18,7 +18,7 @@ import { ProfileSettingsTab } from "./ProfileSettingsTab";
 import { FeedbackSettingsTab } from "./FeedbackSettingsTab";
 import { iosDeviceMenu$ } from "../state/MediaDevices";
 import { useMediaDevices } from "../MediaDevicesContext";
-import { widget } from "../widget";
+import { useHostBridge } from "../HostBridge";
 import {
   useSetting,
   soundEffectVolume as soundEffectVolumeSetting,
@@ -123,6 +123,7 @@ export const SettingsModal: FC<Props> = ({
   // On EC, we decided that it is less confusing for the user if they see those options in the output section
   // rather than the input section.
   const { controlledAudioDevices } = useUrlParams();
+  const hostBridge = useHostBridge();
   // If we are on iOS we will show a button to open the native audio device picker.
   const iosDeviceMenu = useBehavior(iosDeviceMenu$);
 
@@ -234,7 +235,8 @@ export const SettingsModal: FC<Props> = ({
   };
 
   const tabs = [audioTab, videoTab];
-  if (widget === null) tabs.push(profileTab);
+  // The profile is only ours to edit when the account is ours
+  if (hostBridge.supportsProfileChanges) tabs.push(profileTab);
   tabs.push(preferencesTab);
   if (isRageshakeAvailable || import.meta.env.VITE_PACKAGE === "full") {
     // for full package we want to show the analytics consent checkbox
diff --git a/src/settings/__snapshots__/DeveloperSettingsTab.test.tsx.snap b/src/settings/__snapshots__/DeveloperSettingsTab.test.tsx.snap
index 6e3f87d20..63a68ac4b 100644
--- a/src/settings/__snapshots__/DeveloperSettingsTab.test.tsx.snap
+++ b/src/settings/__snapshots__/DeveloperSettingsTab.test.tsx.snap
@@ -380,7 +380,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       local
       )
     </p>
-    <pre>
+    <pre
+      class="_pre_2ddec4"
+    >
       {
   "region": "local",
   "version": "1.2.3"
@@ -390,7 +392,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
     <p>
       Local Participant
     </p>
-    <pre>
+    <pre
+      class="_pre_2ddec4"
+    >
       localParticipantIdentity
     </pre>
     <p>
@@ -417,7 +421,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       remote
       )
     </p>
-    <pre>
+    <pre
+      class="_pre_2ddec4"
+    >
       {
   "region": "remote",
   "version": "4.5.6"
@@ -427,7 +433,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
     <p>
       Local Participant
     </p>
-    <pre>
+    <pre
+      class="_pre_2ddec4"
+    >
       localParticipantIdentity
     </pre>
     <p>
@@ -674,7 +682,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
   <p>
     Environment variables
   </p>
-  <pre>
+  <pre
+    class="_pre_2ddec4"
+  >
     {
   "MY_MOCK_ENV": 10,
   "ENV": "test"
@@ -683,7 +693,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
   <p>
     URL parameters
   </p>
-  <pre>
+  <pre
+    class="_pre_2ddec4"
+  >
     {
   "mocked": true,
   "answer": 42
diff --git a/src/state/AppViewModel.ts b/src/state/AppViewModel.ts
index 7ad91e9dc..3f69515b2 100644
--- a/src/state/AppViewModel.ts
+++ b/src/state/AppViewModel.ts
@@ -5,17 +5,23 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { MediaDevices } from "./MediaDevices";
+import { type AudioOutputOptions, MediaDevices } from "./MediaDevices";
 import { type ObservableScope } from "./ObservableScope";
 
 /**
  * The top-level state holder for the application.
  */
 export class AppViewModel {
-  public readonly mediaDevices = new MediaDevices(this.scope);
+  public readonly mediaDevices = new MediaDevices(
+    this.scope,
+    this.audioOutputOptions,
+  );
 
   // TODO: Move more application logic here. The CallViewModel, at the very
   // least, ought to be accessible from this object.
 
-  public constructor(private readonly scope: ObservableScope) {}
+  public constructor(
+    private readonly scope: ObservableScope,
+    private readonly audioOutputOptions: AudioOutputOptions,
+  ) {}
 }
diff --git a/src/state/CallViewModel/CallViewModel.test.ts b/src/state/CallViewModel/CallViewModel.test.ts
index 181549171..c7783d152 100644
--- a/src/state/CallViewModel/CallViewModel.test.ts
+++ b/src/state/CallViewModel/CallViewModel.test.ts
@@ -68,6 +68,8 @@ import {
 } from "./CallViewModelTestUtils.ts";
 import { MatrixRTCMode } from "../../config/ConfigOptions.ts";
 import { initializeWidget } from "../../widget.ts";
+import { computeUrlParams } from "../../UrlParams.ts";
+import { callViewModelOptionsFromParams } from "./CallViewModel.ts";
 
 initializeWidget();
 
@@ -83,9 +85,6 @@ vi.mock("livekit-client/e2ee-worker?worker");
 
 vi.mock("../e2ee/matrixKeyProvider");
 
-const getUrlParams = vi.hoisted(() => vi.fn(() => ({})));
-vi.mock("../UrlParams", () => ({ getUrlParams }));
-
 const getPlatform = vi.hoisted(() => vi.fn(() => "desktop"));
 vi.mock("../../Platform", () => ({
   get platform(): string {
@@ -1593,12 +1592,13 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
 
   it.skip("audio output changes when toggling earpiece mode", () => {
     withTestScheduler(({ schedule, expectObservable }) => {
-      getUrlParams.mockReturnValue({ controlledAudioDevices: true });
       vi.mocked(ComponentsCore.createMediaDeviceObserver).mockReturnValue(
         of([]),
       );
 
-      const devices = new MediaDevices(testScope());
+      const devices = new MediaDevices(testScope(), {
+        controlledAudioDevices: true,
+      });
 
       window.controls.setAvailableAudioDevices([
         { id: "speaker", name: "Speaker", isSpeaker: true },
@@ -1700,3 +1700,42 @@ describe.each(modes)("CallViewModel (%s mode)", (mode) => {
     });
   });
 });
+
+describe("callViewModelOptionsFromParams", () => {
+  // The defaults on CallViewModelOptions describe a standalone Element Call, so
+  // a widget caller that drops one of these gets standalone behaviour rather
+  // than an error. These check the whole chain from URL to options, which is
+  // where that went wrong for the SDK.
+  const widgetUrl = (extra: string): string =>
+    `#?widgetId=id&parentUrl=${encodeURIComponent("http://parent")}&${extra}`;
+
+  it("carries an explicitly requested notification type", () => {
+    const params = computeUrlParams("", widgetUrl("sendNotificationType=ring"));
+    expect(callViewModelOptionsFromParams(params).sendNotificationType).toBe(
+      "ring",
+    );
+  });
+
+  it("carries the notification type an intent implies", () => {
+    const params = computeUrlParams("", widgetUrl("intent=start_call_dm"));
+    expect(callViewModelOptionsFromParams(params).sendNotificationType).toBe(
+      "ring",
+    );
+  });
+
+  it("carries hideScreensharing", () => {
+    const params = computeUrlParams("", widgetUrl("hideScreensharing=true"));
+    expect(callViewModelOptionsFromParams(params).hideScreensharing).toBe(true);
+  });
+
+  it("carries controlledAudioDevices and the call intent", () => {
+    const params = computeUrlParams(
+      "",
+      widgetUrl("controlledAudioDevices=true&intent=start_call_voice"),
+    );
+    expect(callViewModelOptionsFromParams(params)).toMatchObject({
+      controlledAudioDevices: true,
+      callIntent: "audio",
+    });
+  });
+});
diff --git a/src/state/CallViewModel/CallViewModel.ts b/src/state/CallViewModel/CallViewModel.ts
index aa88e6115..957a56fad 100644
--- a/src/state/CallViewModel/CallViewModel.ts
+++ b/src/state/CallViewModel/CallViewModel.ts
@@ -45,8 +45,9 @@ import {
   MembershipManagerEvent,
   type LivekitTransportConfig,
   type MatrixRTCSession,
+  type RTCCallIntent,
+  type RTCNotificationType,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { type IWidgetApiRequest } from "matrix-widget-api";
 import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";
 import { v4 as uuidv4 } from "uuid";
 import { type IMembershipManager } from "matrix-js-sdk/lib/matrixrtc/IMembershipManager";
@@ -87,9 +88,9 @@ import { constant, type Behavior } from "../Behavior";
 import { E2eeType } from "../../e2ee/e2eeType";
 import { MatrixKeyProvider } from "../../e2ee/matrixKeyProvider";
 import { type MuteStates } from "../MuteStates";
-import { getUrlParams, HeaderStyle } from "../../UrlParams";
+import { HeaderStyle, type UrlParams } from "../../UrlParams";
 import { type ProcessorState } from "../../livekit/TrackProcessorContext";
-import { ElementWidgetActions, widget } from "../../widget";
+import { type HostBridge, nullHostBridge } from "../../HostBridge";
 import {
   layoutShallowEquals,
   type Alignment,
@@ -172,6 +173,28 @@ import { type GridTileViewModel } from "../TileViewModel.ts";
 // callMembership -> rtcMembership
 export interface CallViewModelOptions {
   encryptionSystem: EncryptionSystem;
+  /**
+   * The application hosting Element Call, which can ask it to hang up and wants
+   * to know when the user joins or leaves. Defaults to no host.
+   */
+  hostBridge?: HostBridge;
+  /**
+   * Whether the app hosting Element Call controls the audio output devices,
+   * rather than the browser. Defaults to false.
+   */
+  controlledAudioDevices?: boolean;
+  /** The style of header to show. Defaults to {@link HeaderStyle.Standard}. */
+  header?: HeaderStyle;
+  /** Whether the call controls should be shown. Defaults to true. */
+  showControls?: boolean;
+  /** Whether to hide the screen-sharing button. Defaults to false. */
+  hideScreensharing?: boolean;
+  /**
+   * Whether and what kind of notification to send when joining the call.
+   */
+  sendNotificationType?: RTCNotificationType;
+  /** The kind of call being placed. */
+  callIntent?: RTCCallIntent;
   autoLeaveWhenOthersLeft?: boolean;
   /**
    * If the call is started in a way where we want it to behave like a telephone usecase
@@ -182,8 +205,15 @@ export interface CallViewModelOptions {
   livekitRoomFactory?: (options?: RoomOptions) => LivekitRoom;
   /** Optional behavior overriding the local connection state, mainly for testing purposes. */
   connectionState$?: Behavior<ConnectionState>;
-  /** Optional behavior overriding the computed window size, mainly for testing purposes. */
-  windowSize$?: Behavior<{ width: number; height: number }>;
+  /**
+   * The size of the space the call is drawn in: the page when Element Call
+   * owns it, or the container a host mounted it in when it is a component.
+   * The layout — whether the call is shown full size, flat, narrow or as a
+   * picture-in-picture — follows this rather than the size of the window, so
+   * that a component shrunk by its host adapts even though the window has not
+   * changed.
+   */
+  windowSize$: Behavior<{ width: number; height: number }>;
   /** Optional value overriding the local transport, for testing purposes. */
   localTransport?: LocalTransport;
   /** Optional value overriding the connection factory, for testing purposes. */
@@ -194,6 +224,40 @@ export interface CallViewModelOptions {
   toggleScreensharing?: () => void;
 }
 
+/**
+ * The options {@link createCallViewModel$} takes from the parameters Element
+ * Call was started with.
+ *
+ * Callers share this rather than picking the fields out themselves. The
+ * defaults on {@link CallViewModelOptions} describe a standalone Element Call,
+ * so a widget or component caller that misses one does not get an error — it
+ * quietly gets standalone behaviour instead.
+ *
+ * Note `autoLeaveWhenOthersLeft` and `waitForCallPickup` are deliberately not
+ * here: unlike these, the view model never read them from the parameters
+ * itself, so they remain the caller's decision.
+ */
+export function callViewModelOptionsFromParams(
+  params: UrlParams,
+): Pick<
+  CallViewModelOptions,
+  | "controlledAudioDevices"
+  | "header"
+  | "showControls"
+  | "hideScreensharing"
+  | "sendNotificationType"
+  | "callIntent"
+> {
+  return {
+    controlledAudioDevices: params.controlledAudioDevices,
+    header: params.header,
+    showControls: params.showControls,
+    hideScreensharing: params.hideScreensharing,
+    sendNotificationType: params.sendNotificationType,
+    callIntent: params.callIntent,
+  };
+}
+
 // Do not play any sounds if the participant count has exceeded this
 // number.
 export const MAX_PARTICIPANT_COUNT_FOR_SOUND = 8;
@@ -207,6 +271,11 @@ const smallMobileCallThreshold = 3;
 // with the interface
 const showFooterMs = 4000;
 
+/**
+ * The general shape of the space the call is drawn in. Called a window because
+ * that is what it is in the standalone app; for a component it is the container
+ * the host gave us, which may be a small corner of a large window.
+ */
 export type WindowMode = "normal" | "narrow" | "flat" | "pip";
 
 interface LayoutScanState {
@@ -441,6 +510,18 @@ export function createCallViewModel$(
   if (!(userId && deviceId))
     throw new UnknownCallError(new Error("userId and deviceId are required"));
 
+  // Defaults match what the URL parameters resolve to outside of widget mode,
+  // so that callers which don't care (chiefly tests) behave as they always have.
+  const {
+    hostBridge = nullHostBridge,
+    controlledAudioDevices = false,
+    header = HeaderStyle.Standard,
+    showControls = true,
+    hideScreensharing = false,
+    sendNotificationType,
+    callIntent,
+  } = options;
+
   const livekitKeyProvider = getE2eeKeyProvider(
     options.encryptionSystem,
     matrixRTCSession,
@@ -505,7 +586,7 @@ export function createCallViewModel$(
       mediaDevices,
       trackProcessorState$,
       livekitKeyProvider,
-      getUrlParams().controlledAudioDevices,
+      controlledAudioDevices,
       options.livekitRoomFactory,
     );
 
@@ -558,6 +639,8 @@ export function createCallViewModel$(
           encryptMedia: livekitKeyProvider !== undefined,
           matrixRTCMode,
           delayedLeaveTimings,
+          sendNotificationType,
+          callIntent,
         },
       );
     },
@@ -570,6 +653,7 @@ export function createCallViewModel$(
         logger.getChild(
           "[Publisher " + connection.transport.livekit_service_url + "]",
         ),
+        controlledAudioDevices,
       );
     },
     connectionManager,
@@ -577,6 +661,8 @@ export function createCallViewModel$(
     matrixRTCSession,
     localTransport,
     roomId: matrixRoom.roomId,
+    hideScreensharing,
+    hostBridge,
     baseUrl: client.baseUrl,
     ownMembershipIdentity,
     delayId$: scope.behavior(
@@ -881,24 +967,16 @@ export function createCallViewModel$(
 
   const userHangup$ = new Subject<void>();
 
-  const widgetHangup$ =
-    widget === null
-      ? NEVER
-      : (
-          fromEvent(
-            widget.lazyActions,
-            ElementWidgetActions.HangupCall,
-          ) as Observable<CustomEvent<IWidgetApiRequest>>
-        ).pipe(
-          tap((ev) => {
-            widget!.api.transport.reply(ev.detail, {});
-          }),
-        );
+  const hostHangup$ = hostBridge.hangUp$.pipe(
+    tap((request) => {
+      request.reply();
+    }),
+  );
 
   const leave$: Observable<"user" | "timeout" | "decline" | "allOthersLeft"> =
     merge(
       autoLeave$,
-      merge(userHangup$, widgetHangup$).pipe(map(() => "user" as const)),
+      merge(userHangup$, hostHangup$).pipe(map(() => "user" as const)),
     ).pipe(scope.share);
 
   const spotlightSpeaker$ = scope.behavior<UserMediaViewModel | undefined>(
@@ -1023,18 +1101,10 @@ export function createCallViewModel$(
 
   const pipEnabled$ = scope.behavior(setPipEnabled$, false);
 
-  const windowSize$ =
-    options.windowSize$ ??
-    scope.behavior<{ width: number; height: number }>(
-      fromEvent(window, "resize").pipe(
-        startWith(null),
-        map(() => ({ width: window.innerWidth, height: window.innerHeight })),
-      ),
-    );
-
-  // A guess at what the window's mode should be based on its size and shape.
+  // A guess at what the window's mode should be based on the size and shape of
+  // the space we have to draw in.
   const naturalWindowMode$ = scope.behavior<WindowMode>(
-    windowSize$.pipe(
+    options.windowSize$.pipe(
       map(({ width, height }) => {
         if (height <= 400 && width <= 340) return "pip";
         // Our layouts for flat windows are better at adapting to a small width
@@ -1449,9 +1519,8 @@ export function createCallViewModel$(
     ),
   );
 
-  const urlParams = getUrlParams();
   const showFooterUrlParams = !(
-    urlParams.header === HeaderStyle.None && urlParams.showControls === false
+    header === HeaderStyle.None && showControls === false
   );
   const showFooter$ = scope.behavior(
     naturallyShowFooter$.pipe(
@@ -1770,8 +1839,7 @@ export function createCallViewModel$(
   return {
     autoLeave$: autoLeave$,
     ringingVm$: ringingMedia$,
-    ringingStatusLocation:
-      urlParams.header === HeaderStyle.AppBar ? "app_bar" : "tile",
+    ringingStatusLocation: header === HeaderStyle.AppBar ? "app_bar" : "tile",
     leave$: leave$,
     hangup: (): void => userHangup$.next(),
     join: localMembership.requestJoinAndPublish,
diff --git a/src/state/CallViewModel/localMember/LocalMember.test.ts b/src/state/CallViewModel/localMember/LocalMember.test.ts
index e7c5b1e45..6df999b1e 100644
--- a/src/state/CallViewModel/localMember/LocalMember.test.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.test.ts
@@ -60,6 +60,7 @@ import { ConnectionManagerData } from "../remoteMembers/ConnectionManager";
 import { ConnectionState, type Connection } from "../remoteMembers/Connection";
 import { type Publisher } from "./Publisher";
 import { initializeWidget } from "../../../widget";
+import { nullHostBridge } from "../../../HostBridge";
 import {
   type LocalTransport,
   type LocalTransportWithSFUConfig,
@@ -233,6 +234,8 @@ describe("LocalMembership", () => {
       rtsSession$: constant(RTCMemberStatus.Connected),
     },
     roomId: "!test-room-id:example.org",
+    hideScreensharing: false,
+    hostBridge: nullHostBridge,
     baseUrl: "https://matrix.example.org",
     ownMembershipIdentity: ownMemberMock,
     client: mockedClient,
diff --git a/src/state/CallViewModel/localMember/LocalMember.ts b/src/state/CallViewModel/localMember/LocalMember.ts
index 7805805b8..7303946a0 100644
--- a/src/state/CallViewModel/localMember/LocalMember.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.ts
@@ -21,6 +21,8 @@ import {
   type LivekitTransport,
   type LivekitTransportConfig,
   type MatrixRTCSession,
+  type RTCCallIntent,
+  type RTCNotificationType,
 } from "matrix-js-sdk/lib/matrixrtc";
 import {
   BehaviorSubject,
@@ -52,8 +54,8 @@ import {
   MembershipManagerError,
   UnknownCallError,
 } from "../../../utils/errors.ts";
-import { ElementWidgetActions, widget } from "../../../widget.ts";
-import { getUrlParams } from "../../../UrlParams.ts";
+import { type HostBridge } from "../../../HostBridge.ts";
+
 import { PosthogAnalytics } from "../../../analytics/PosthogAnalytics.ts";
 import {
   advancedScreenShare,
@@ -152,6 +154,10 @@ interface Props {
     MatrixRTCSession,
     "updateCallIntent" | "leaveRoomSession"
   >;
+  /** Whether to hide the screen-sharing button. */
+  hideScreensharing: boolean;
+  /** The application hosting Element Call, to be kept informed of join/leave. */
+  hostBridge: HostBridge;
   baseUrl: string;
   delayId$: Behavior<string | null>;
   matrixRTCMode: MatrixRTCMode;
@@ -176,6 +182,8 @@ interface Props {
  * @param props.baseUrl Base URL of the homeserver.
  * @param props.delayId$ ID of the delayed leave event to delegate to the SFU.
  * @param props.roomId The room ID used as the call identifier in analytics events.
+ * @param props.hideScreensharing Whether to hide the screen-sharing button.
+ * @param props.hostBridge The application hosting Element Call.
  * @returns
  *  - publisher: The handle to create tracks and publish them to the room.
  *  - connected$: the current connection state. Including matrix server and livekit server connection. (only considering the livekit server we are using for our own media publication)
@@ -196,6 +204,8 @@ export const createLocalMembership$ = ({
   matrixRTCSession,
   baseUrl,
   roomId,
+  hideScreensharing,
+  hostBridge,
   ownMembershipIdentity,
   delayId$,
   matrixRTCMode,
@@ -640,29 +650,24 @@ export const createLocalMembership$ = ({
       }
     });
 
-  // inform the widget about the connect and disconnect intent from the user.
+  // inform the host about the connect and disconnect intent from the user.
   scope
     .behavior(joinAndPublishRequested$.pipe(pairwise(), scope.bind()), [
       undefined,
       joinAndPublishRequested$.value,
     ])
     .subscribe(([prev, current]) => {
-      if (!widget) return;
       // JOIN prev=false (was left) => current-true (now joiend)
       if (!prev && current) {
-        widget.api.transport
-          .send(ElementWidgetActions.JoinCall, {})
-          .catch((e) => {
-            logger.error("Failed to send join action", e);
-          });
+        hostBridge.notifyJoined().catch((e) => {
+          logger.error("Failed to notify the host that we joined", e);
+        });
       }
       // LEAVE prev=false (was joined) => current-true (now left)
       if (prev && !current) {
-        widget.api.transport
-          .send(ElementWidgetActions.HangupCall, {})
-          .catch((e) => {
-            logger.error("Failed to send hangup action", e);
-          });
+        hostBridge.notifyHungUp().catch((e) => {
+          logger.error("Failed to notify the host that we hung up", e);
+        });
       }
     });
 
@@ -812,7 +817,7 @@ export const createLocalMembership$ = ({
   let toggleScreenSharing: (() => void) | null = null;
   if (
     "getDisplayMedia" in (navigator.mediaDevices ?? {}) &&
-    !getUrlParams().hideScreensharing
+    !hideScreensharing
   ) {
     toggleScreenSharing = (): void => {
       const screenshareSettings: ScreenShareCaptureOptions = {
@@ -962,6 +967,10 @@ interface EnterRTCSessionOptions {
   encryptMedia: boolean;
   matrixRTCMode: MatrixRTCMode;
   delayedLeaveTimings: ResolvedDelayedLeaveTimings;
+  /** Whether and what kind of notification to send when joining. */
+  sendNotificationType?: RTCNotificationType;
+  /** The kind of call being placed. */
+  callIntent?: RTCCallIntent;
 }
 
 /**
@@ -974,16 +983,24 @@ interface EnterRTCSessionOptions {
  * @param rtcSession - The MatrixRTCSession to join.
  * @param ownMembershipIdentity - Options for entering the RTC session.
  * @param transport - The LivekitTransport to use for this session.
- * @param delayedLeaveTimings - The preferred timings for delayed leave events.
- * @param options - `encryptMedia`: Whether to encrypt media `matrixRTCMode`: The Matrix RTC mode to use.
- * @throws If the widget could not send ElementWidgetActions.JoinCall action.
+ * @param options - `encryptMedia`: Whether to encrypt media. `matrixRTCMode`: The
+ *   Matrix RTC mode to use. `delayedLeaveTimings`: The preferred timings for
+ *   delayed leave events. `sendNotificationType`: Whether and what kind of
+ *   notification to send on join. `callIntent`: The kind of call being placed.
+ * @throws If the host could not be told that we are joining.
  */
 // Exported for unit testing
 export function enterRTCSession(
   rtcSession: MatrixRTCSession,
   ownMembershipIdentity: CallMembershipIdentityParts,
   transport: LivekitTransportConfig,
-  { encryptMedia, matrixRTCMode, delayedLeaveTimings }: EnterRTCSessionOptions,
+  {
+    encryptMedia,
+    matrixRTCMode,
+    delayedLeaveTimings,
+    sendNotificationType: notificationType,
+    callIntent,
+  }: EnterRTCSessionOptions,
 ): void {
   PosthogAnalytics.instance.eventCallEnded.cacheStartCall(new Date());
   PosthogAnalytics.instance.eventCallStarted.track(rtcSession.room.roomId);
@@ -997,7 +1014,6 @@ export function enterRTCSession(
     matrix_rtc_session: sessionConfig,
   } = Config.get();
   const retryInterval = sessionConfig.network_error_retry_ms;
-  const { sendNotificationType: notificationType, callIntent } = getUrlParams();
   const multiSFU =
     matrixRTCMode === MatrixRTCMode.Compatibility ||
     matrixRTCMode === MatrixRTCMode.Matrix_2_0;
diff --git a/src/state/CallViewModel/localMember/Publisher.test.ts b/src/state/CallViewModel/localMember/Publisher.test.ts
index 21775c58d..5d9f03784 100644
--- a/src/state/CallViewModel/localMember/Publisher.test.ts
+++ b/src/state/CallViewModel/localMember/Publisher.test.ts
@@ -192,6 +192,7 @@ describe("Publisher", () => {
       muteStates,
       constant({ supported: false, processor: undefined }),
       logger,
+      false,
     );
   });
 
@@ -309,6 +310,7 @@ describe("Publisher", () => {
         muteStates,
         constant({ supported: false, processor: undefined }),
         logger,
+        false,
       );
     });
     afterEach(async () => {
@@ -364,6 +366,7 @@ describe("Bug fix", () => {
       muteStates,
       constant({ supported: false, processor: undefined }),
       logger,
+      false,
     );
     audioEnabled$.next(true);
 
diff --git a/src/state/CallViewModel/localMember/Publisher.ts b/src/state/CallViewModel/localMember/Publisher.ts
index 0d5f263a6..5353a98d4 100644
--- a/src/state/CallViewModel/localMember/Publisher.ts
+++ b/src/state/CallViewModel/localMember/Publisher.ts
@@ -29,7 +29,7 @@ import {
   type ProcessorState,
   trackProcessorSync,
 } from "../../../livekit/TrackProcessorContext.tsx";
-import { getUrlParams } from "../../../UrlParams.ts";
+
 import { observeTrackReference$ } from "../../observeTrackReference";
 import { type Connection } from "../remoteMembers/Connection.ts";
 import { ObservableScope } from "../../ObservableScope.ts";
@@ -56,6 +56,8 @@ export class Publisher {
    * @param muteStates - The mute states for audio and video.
    * @param trackerProcessorState$ - The processor state for the video track processor (e.g. background blur).
    * @param logger - The logger to use for logging :D.
+   * @param controlledAudioDevices - Whether the app hosting Element Call
+   *   controls the audio output devices, rather than the browser.
    */
   public constructor(
     private connection: Pick<Connection, "livekitRoom" | "state$">, //setE2EEEnabled,
@@ -63,8 +65,8 @@ export class Publisher {
     private readonly muteStates: MuteStates,
     trackerProcessorState$: Behavior<ProcessorState>,
     private logger: Logger,
+    controlledAudioDevices: boolean,
   ) {
-    const { controlledAudioDevices } = getUrlParams();
     const room = connection.livekitRoom;
 
     room.setE2EEEnabled(room.options.e2ee !== undefined)?.catch((e: Error) => {
diff --git a/src/state/CallViewModelWidget.test.ts b/src/state/CallViewModelWidget.test.ts
index 2f331bd32..dd2e75ab8 100644
--- a/src/state/CallViewModelWidget.test.ts
+++ b/src/state/CallViewModelWidget.test.ts
@@ -6,39 +6,31 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { it, vi, expect } from "vitest";
-import EventEmitter from "events";
+import { Subject } from "rxjs";
 
 // import * as ComponentsCore from "@livekit/components-core";
 import { withCallViewModel } from "./CallViewModel/CallViewModelTestUtils.ts";
 import { type CallViewModel } from "./CallViewModel/CallViewModel.ts";
 import { constant } from "./Behavior.ts";
 import { aliceParticipant, localRtcMember } from "../utils/test-fixtures.ts";
-import { ElementWidgetActions, widget } from "../widget.ts";
+import {
+  type HostBridge,
+  type HostRequest,
+  nullHostBridge,
+} from "../HostBridge.ts";
 import { E2eeType } from "../e2ee/e2eeType.ts";
 import { MatrixRTCMode } from "../config/ConfigOptions.ts";
 
 vi.mock("@livekit/components-core", { spy: true });
 
-vi.mock("../widget", () => ({
-  ElementWidgetActions: {
-    HangupCall: "HangupCall",
-    // Add other actions if needed
-  },
-  widget: {
-    api: {
-      transport: {
-        send: vi.fn().mockResolvedValue(undefined),
-        reply: vi.fn().mockResolvedValue(undefined),
-      },
-    },
-    lazyActions: new EventEmitter(),
-  },
-}));
-
 it.each([[MatrixRTCMode.Compatibility], [MatrixRTCMode.Matrix_2_0]])(
-  "expect leave when ElementWidgetActions.HangupCall is called (%s mode)",
+  "expect leave when the host asks us to hang up (%s mode)",
   async (mode) => {
     const pr = Promise.withResolvers<string>();
+    const hangUp$ = new Subject<HostRequest<Record<string, never>>>();
+    const hostBridge: HostBridge = { ...nullHostBridge, hangUp$ };
+    const reply = vi.fn();
+
     withCallViewModel(mode)(
       {
         remoteParticipants$: constant([aliceParticipant]),
@@ -49,25 +41,17 @@ it.each([[MatrixRTCMode.Compatibility], [MatrixRTCMode.Matrix_2_0]])(
           pr.resolve(s);
         });
 
-        widget!.lazyActions!.emit(
-          ElementWidgetActions.HangupCall,
-          new CustomEvent(ElementWidgetActions.HangupCall, {
-            detail: {
-              action: "im.vector.hangup",
-              api: "toWidget",
-              data: {},
-              requestId: "widgetapi-1761237395918",
-              widgetId: "mrUjS9T6uKUOWHMxXvLbSv0F",
-            },
-          }),
-        );
+        hangUp$.next({ data: {}, reply });
       },
       {
         encryptionSystem: { kind: E2eeType.PER_PARTICIPANT },
+        hostBridge,
       },
     );
 
     const source = await pr.promise;
     expect(source).toBe("user");
+    // The host expects to hear back that we acted on its request
+    expect(reply).toHaveBeenCalledOnce();
   },
 );
diff --git a/src/state/MediaDevices.test.ts b/src/state/MediaDevices.test.ts
new file mode 100644
index 000000000..f65b024e2
--- /dev/null
+++ b/src/state/MediaDevices.test.ts
@@ -0,0 +1,59 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test, vi } from "vitest";
+import { of } from "rxjs";
+
+const getPlatform = vi.hoisted(() => vi.fn(() => "desktop"));
+vi.mock("../Platform", () => ({
+  get platform(): string {
+    return getPlatform();
+  },
+  isFirefox: (): boolean => false,
+}));
+vi.mock("@livekit/components-core", () => ({
+  createMediaDeviceObserver: () => of([]),
+}));
+
+import { AudioOutput, MediaDevices } from "./MediaDevices";
+import { AndroidControlledAudioOutput } from "./AndroidControlledAudioOutput";
+import { IOSControlledAudioOutput } from "./IOSControlledAudioOutput";
+import { ObservableScope } from "./ObservableScope";
+
+// Which audio output implementation is used is decided by what the app hosting
+// Element Call told it, rather than being discovered from the environment.
+describe("MediaDevices audio output", () => {
+  test("uses the browser's own output when nobody else is controlling it", () => {
+    const devices = new MediaDevices(new ObservableScope(), {
+      controlledAudioDevices: false,
+    });
+
+    expect(devices.audioOutput).toBeInstanceOf(AudioOutput);
+  });
+
+  test("hands control to the host on Android", () => {
+    getPlatform.mockReturnValue("android");
+
+    const devices = new MediaDevices(new ObservableScope(), {
+      controlledAudioDevices: true,
+      callIntent: "audio",
+    });
+
+    expect(devices.audioOutput).toBeInstanceOf(AndroidControlledAudioOutput);
+  });
+
+  test("hands control to the host elsewhere too", () => {
+    getPlatform.mockReturnValue("ios");
+
+    const devices = new MediaDevices(new ObservableScope(), {
+      controlledAudioDevices: true,
+      callIntent: "video",
+    });
+
+    expect(devices.audioOutput).toBeInstanceOf(IOSControlledAudioOutput);
+  });
+});
diff --git a/src/state/MediaDevices.ts b/src/state/MediaDevices.ts
index 70a676cf5..4610bab66 100644
--- a/src/state/MediaDevices.ts
+++ b/src/state/MediaDevices.ts
@@ -16,6 +16,7 @@ import {
 } from "rxjs";
 import { createMediaDeviceObserver } from "@livekit/components-core";
 import { type Logger, logger as rootLogger } from "matrix-js-sdk/lib/logger";
+import { type RTCCallIntent } from "matrix-js-sdk/lib/matrixrtc";
 
 import {
   alwaysShowIphoneEarpiece as alwaysShowIphoneEarpieceSetting,
@@ -25,7 +26,6 @@ import {
 } from "../settings/settings";
 import { type ObservableScope } from "./ObservableScope";
 import { availableOutputDevices$ as controlledAvailableOutputDevices$ } from "../controls";
-import { getUrlParams } from "../UrlParams";
 import { platform } from "../Platform";
 import { switchWhen } from "../utils/observable";
 import { type Behavior, constant } from "./Behavior";
@@ -338,6 +338,22 @@ class VideoInput implements MediaDevice<DeviceLabel, SelectedDevice> {
   }
 }
 
+/**
+ * How Element Call should manage audio output.
+ */
+export interface AudioOutputOptions {
+  /**
+   * Whether the list of output devices is controlled by the app hosting Element
+   * Call, through the global JS controls, rather than by the browser.
+   */
+  controlledAudioDevices: boolean;
+  /**
+   * The kind of call being placed, which decides the initial output route when
+   * the host controls the devices.
+   */
+  callIntent?: RTCCallIntent;
+}
+
 export class MediaDevices {
   private readonly deviceNamesRequest$ = new Subject<void>();
   /**
@@ -368,23 +384,28 @@ export class MediaDevices {
   public readonly audioOutput: MediaDevice<
     AudioOutputDeviceLabel,
     SelectedAudioOutputDevice
-  > = getUrlParams().controlledAudioDevices
+  > = this.audioOutputOptions.controlledAudioDevices
     ? platform == "android"
       ? new AndroidControlledAudioOutput(
           controlledAvailableOutputDevices$,
           this.scope,
-          getUrlParams().callIntent,
+          this.audioOutputOptions.callIntent,
           window.controls,
         )
       : new IOSControlledAudioOutput(
           this.usingNames$,
           this.scope,
-          getUrlParams().callIntent,
+          this.audioOutputOptions.callIntent,
         )
     : new AudioOutput(this.usingNames$, this.scope);
 
   public readonly videoInput: MediaDevice<DeviceLabel, SelectedDevice> =
     new VideoInput(this.usingNames$, this.scope);
 
-  public constructor(private readonly scope: ObservableScope) {}
+  // Note: both parameters are read by the field initializers above, which is
+  // safe because TypeScript assigns parameter properties before running them.
+  public constructor(
+    private readonly scope: ObservableScope,
+    private readonly audioOutputOptions: AudioOutputOptions,
+  ) {}
 }
diff --git a/src/state/MuteStates.test.ts b/src/state/MuteStates.test.ts
index f594cb05c..efccd70be 100644
--- a/src/state/MuteStates.test.ts
+++ b/src/state/MuteStates.test.ts
@@ -6,14 +6,22 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
-import { BehaviorSubject } from "rxjs";
+import { BehaviorSubject, NEVER, Subject } from "rxjs";
 import { logger } from "matrix-js-sdk/lib/logger";
 
+import {
+  type DeviceMuteRequest,
+  type DeviceMuteState,
+  type HostBridge,
+  type HostRequest,
+  nullHostBridge,
+} from "../HostBridge";
 import { MuteStates, MuteState } from "./MuteStates";
 import {
   type AudioOutputDeviceLabel,
   type DeviceLabel,
   type MediaDevice,
+  type SelectedAudioInputDevice,
   type SelectedAudioOutputDevice,
   type SelectedDevice,
 } from "./MediaDevices";
@@ -220,6 +228,80 @@ describe("MuteStates", () => {
     };
   }
 
+  function aAudioInput(): MediaDevice<DeviceLabel, SelectedAudioInputDevice> {
+    return {
+      available$: constant(
+        new Map<string, DeviceLabel>([
+          ["mic0", { type: "name", name: "Built-in Microphone" }],
+        ]),
+      ),
+      selected$: constant({ id: "mic0", hardwareDeviceChange$: NEVER }),
+      select(): void {},
+    };
+  }
+
+  test("keeps the host informed and applies its mute requests", async () => {
+    const deviceMute$ = new Subject<
+      HostRequest<DeviceMuteRequest, DeviceMuteState>
+    >();
+    const notifyDeviceMute = vi.fn(async (): Promise<void> => {});
+    const hostBridge: HostBridge = {
+      ...nullHostBridge,
+      notifyDeviceMute,
+      deviceMute$,
+    };
+    const muteStates = new MuteStates(
+      testScope,
+      mockMediaDevices({
+        audioInput: aAudioInput(),
+        videoInput: aVideoInput(),
+      }),
+      { audioEnabled: true, videoEnabled: false },
+      hostBridge,
+    );
+    await flushPromises();
+
+    // The host hears the state we started in
+    expect(notifyDeviceMute).toHaveBeenLastCalledWith({
+      audio_enabled: true,
+      video_enabled: false,
+    });
+
+    // The host asks for the camera on, saying nothing about the microphone,
+    // which is left as it is
+    const reply = vi.fn();
+    deviceMute$.next({ data: { video_enabled: true }, reply });
+    await flushPromises();
+    expect(reply).toHaveBeenCalledExactlyOnceWith({
+      audio_enabled: true,
+      video_enabled: true,
+    });
+    expect(muteStates.audio.enabled$.value).toBe(true);
+    expect(muteStates.video.enabled$.value).toBe(true);
+    expect(notifyDeviceMute).toHaveBeenLastCalledWith({
+      audio_enabled: true,
+      video_enabled: true,
+    });
+
+    // Then for everything off
+    const replyAgain = vi.fn();
+    deviceMute$.next({
+      data: { audio_enabled: false, video_enabled: false },
+      reply: replyAgain,
+    });
+    await flushPromises();
+    expect(replyAgain).toHaveBeenCalledExactlyOnceWith({
+      audio_enabled: false,
+      video_enabled: false,
+    });
+    expect(muteStates.audio.enabled$.value).toBe(false);
+    expect(muteStates.video.enabled$.value).toBe(false);
+    expect(notifyDeviceMute).toHaveBeenLastCalledWith({
+      audio_enabled: false,
+      video_enabled: false,
+    });
+  });
+
   test("should mute camera when in earpiece mode", async () => {
     const audioOutputDevice = aAudioOutputDevices();
 
@@ -228,10 +310,12 @@ describe("MuteStates", () => {
       videoInput: aVideoInput(),
       // other devices are not relevant for this test
     });
-    const muteStates = new MuteStates(testScope, mediaDevices, {
-      audioEnabled: false,
-      videoEnabled: false,
-    });
+    const muteStates = new MuteStates(
+      testScope,
+      mediaDevices,
+      { audioEnabled: false, videoEnabled: false },
+      nullHostBridge,
+    );
 
     let latestSyncedState: boolean | null = null;
     muteStates.video.setHandler(async (enabled: boolean): Promise<boolean> => {
diff --git a/src/state/MuteStates.ts b/src/state/MuteStates.ts
index d89cb8442..59413b036 100644
--- a/src/state/MuteStates.ts
+++ b/src/state/MuteStates.ts
@@ -6,14 +6,12 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type IWidgetApiRequest } from "matrix-widget-api";
 import { logger } from "matrix-js-sdk/lib/logger";
 import {
   BehaviorSubject,
   combineLatest,
   distinctUntilChanged,
   firstValueFrom,
-  fromEvent,
   map,
   merge,
   Observable,
@@ -24,7 +22,7 @@ import {
 } from "rxjs";
 
 import { type MediaDevices, type MediaDevice } from "../state/MediaDevices";
-import { ElementWidgetActions, widget } from "../widget";
+import { type DeviceMuteState, type HostBridge } from "../HostBridge";
 import { type ObservableScope } from "./ObservableScope";
 import { type Behavior, constant } from "./Behavior";
 
@@ -216,58 +214,51 @@ export class MuteStates {
       audioEnabled: boolean;
       videoEnabled: boolean;
     },
+    hostBridge: HostBridge,
   ) {
-    if (widget !== null) {
-      // Sync our mute states with the hosting client
-      const widgetApiState$ = combineLatest(
-        [this.audio.enabled$, this.video.enabled$],
-        (audio, video) => ({ audio_enabled: audio, video_enabled: video }),
-      );
-      widgetApiState$.pipe(this.scope.bind()).subscribe((state) => {
-        widget!.api.transport
-          .send(ElementWidgetActions.DeviceMute, state)
-          .catch((e) =>
-            logger.warn("Could not send DeviceMute action to widget", e),
-          );
-      });
+    // Keep the host informed of our mute state
+    const muteState$ = combineLatest(
+      [this.audio.enabled$, this.video.enabled$],
+      (audio, video): DeviceMuteState => ({
+        audio_enabled: audio,
+        video_enabled: video,
+      }),
+    );
+    muteState$.pipe(this.scope.bind()).subscribe((state) => {
+      hostBridge
+        .notifyDeviceMute(state)
+        .catch((e) => logger.warn("Could not send mute state to the host", e));
+    });
 
-      // Also sync the hosting client's mute states back with ours
-      const muteActions$ = fromEvent(
-        widget.lazyActions,
-        ElementWidgetActions.DeviceMute,
-      ) as Observable<CustomEvent<IWidgetApiRequest>>;
-      muteActions$
-        .pipe(
-          withLatestFrom(
-            widgetApiState$,
-            this.audio.setEnabled$,
-            this.video.setEnabled$,
-          ),
-          this.scope.bind(),
-        )
-        .subscribe(([ev, state, setAudioEnabled, setVideoEnabled]) => {
-          // First copy the current state into our new state
-          const newState = { ...state };
-          // Update new state if there are any requested changes from the widget
-          // action in `ev.detail.data`.
-          if (
-            ev.detail.data.audio_enabled != null &&
-            typeof ev.detail.data.audio_enabled === "boolean" &&
-            setAudioEnabled !== null
-          ) {
-            newState.audio_enabled = ev.detail.data.audio_enabled;
-            setAudioEnabled(newState.audio_enabled);
-          }
-          if (
-            ev.detail.data.video_enabled != null &&
-            typeof ev.detail.data.video_enabled === "boolean" &&
-            setVideoEnabled !== null
-          ) {
-            newState.video_enabled = ev.detail.data.video_enabled;
-            setVideoEnabled(newState.video_enabled);
-          }
-          widget!.api.transport.reply(ev.detail, newState);
-        });
-    }
+    // And apply the changes the host asks for
+    hostBridge.deviceMute$
+      .pipe(
+        withLatestFrom(
+          muteState$,
+          this.audio.setEnabled$,
+          this.video.setEnabled$,
+        ),
+        this.scope.bind(),
+      )
+      .subscribe(([request, state, setAudioEnabled, setVideoEnabled]) => {
+        // First copy the current state into our new state
+        const newState = { ...state };
+        // Then apply whichever changes the host asked for
+        if (
+          typeof request.data.audio_enabled === "boolean" &&
+          setAudioEnabled !== null
+        ) {
+          newState.audio_enabled = request.data.audio_enabled;
+          setAudioEnabled(newState.audio_enabled);
+        }
+        if (
+          typeof request.data.video_enabled === "boolean" &&
+          setVideoEnabled !== null
+        ) {
+          newState.video_enabled = request.data.video_enabled;
+          setVideoEnabled(newState.video_enabled);
+        }
+        request.reply(newState);
+      });
   }
 }
diff --git a/src/state/initialMuteState.test.ts b/src/state/initialMuteState.test.ts
index abbb52cde..020a80b8c 100644
--- a/src/state/initialMuteState.test.ts
+++ b/src/state/initialMuteState.test.ts
@@ -12,21 +12,21 @@ import { calculateInitialMuteState } from "./initialMuteState";
 
 test.each<{
   callIntent: RTCCallIntent;
-  isWidgetMode: boolean;
+  allowJoinUnmutedViaIntent: boolean;
 }>([
-  { callIntent: "audio", isWidgetMode: false },
-  { callIntent: "audio", isWidgetMode: true },
-  { callIntent: "video", isWidgetMode: false },
-  { callIntent: "video", isWidgetMode: true },
-  { callIntent: "unknown", isWidgetMode: false },
-  { callIntent: "unknown", isWidgetMode: true },
+  { callIntent: "audio", allowJoinUnmutedViaIntent: false },
+  { callIntent: "audio", allowJoinUnmutedViaIntent: true },
+  { callIntent: "video", allowJoinUnmutedViaIntent: false },
+  { callIntent: "video", allowJoinUnmutedViaIntent: true },
+  { callIntent: "unknown", allowJoinUnmutedViaIntent: false },
+  { callIntent: "unknown", allowJoinUnmutedViaIntent: true },
 ])(
-  "Should allow to unmute on start if not skipping lobby (callIntent: $callIntent, packageType: $packageType)",
-  ({ callIntent, isWidgetMode }) => {
+  "Should allow to unmute on start if not skipping lobby (callIntent: $callIntent, allowJoinUnmutedViaIntent: $allowJoinUnmutedViaIntent)",
+  ({ callIntent, allowJoinUnmutedViaIntent }) => {
     const { audioEnabled, videoEnabled } = calculateInitialMuteState(
       false,
       callIntent,
-      isWidgetMode,
+      allowJoinUnmutedViaIntent,
     );
     expect(audioEnabled).toBe(true);
     expect(videoEnabled).toBe(callIntent !== "audio");
@@ -40,7 +40,7 @@ test.each<{
   { callIntent: "video" },
   { callIntent: "unknown" },
 ])(
-  "Should always mute on start if skipping lobby on non widget mode (callIntent: $callIntent)",
+  "Should always mute on start if skipping lobby and the host does not vouch for the intent (callIntent: $callIntent)",
   ({ callIntent }) => {
     const { audioEnabled, videoEnabled } = calculateInitialMuteState(
       true,
@@ -59,7 +59,7 @@ test.each<{
   { callIntent: "video" },
   { callIntent: "unknown" },
 ])(
-  "Can start unmuted if skipping lobby on widget mode (callIntent: $callIntent)",
+  "Can start unmuted if skipping lobby and the host vouches for the intent (callIntent: $callIntent)",
   ({ callIntent }) => {
     const { audioEnabled, videoEnabled } = calculateInitialMuteState(
       true,
diff --git a/src/state/initialMuteState.ts b/src/state/initialMuteState.ts
index 4d27cddad..51342e895 100644
--- a/src/state/initialMuteState.ts
+++ b/src/state/initialMuteState.ts
@@ -11,30 +11,37 @@ import { type RTCCallIntent } from "matrix-js-sdk/lib/matrixrtc";
 /**
  * Calculates the initial mute state for media devices based on configuration.
  *
- * It is not always possible to start the widget with audio/video unmuted due to privacy concerns.
- * This function encapsulates the logic to determine the appropriate initial state.
+ * It is not always possible to start the call with audio/video unmuted due to
+ * privacy concerns. This function encapsulates the logic to determine the
+ * appropriate initial state.
+ *
+ * @param allowJoinUnmutedViaIntent Whether the host vouches for the intent
+ *   enough to start the user unmuted without a lobby (see
+ *   `HostBridge.allowJoinUnmutedViaIntent`).
  */
 export function calculateInitialMuteState(
   skipLobby: boolean,
   callIntent: RTCCallIntent | undefined,
-  isWidgetMode: boolean,
+  allowJoinUnmutedViaIntent: boolean,
 ): { audioEnabled: boolean; videoEnabled: boolean } {
   logger.debug(
-    `calculateInitialMuteState: skipLobby=${skipLobby}, callIntent=${callIntent} isWidgetMode=${isWidgetMode}`,
+    `calculateInitialMuteState: skipLobby=${skipLobby}, callIntent=${callIntent} allowJoinUnmutedViaIntent=${allowJoinUnmutedViaIntent}`,
   );
 
-  if (skipLobby && !isWidgetMode) {
-    // If not in widget mode and lobby is skipped, default to muted to protect user privacy.
-    // In the SPA context we don't want to unmute users without giving them a chance to adjust their settings first.
+  if (skipLobby && !allowJoinUnmutedViaIntent) {
+    // The lobby is skipped, so the user gets no chance to adjust their devices
+    // before joining, and nobody has vouched for the intent: default to muted
+    // to protect their privacy.
     return {
       audioEnabled: false,
       videoEnabled: false,
     };
   }
 
-  // Embedded contexts are trusted environments, so they allow unmuted by default.
-  // Same for when showing a lobby, as users can adjust their settings there.
-  // Additionally, if the call intent is "audio", we disable video by default.
+  // A host that vouches for the intent is a trusted environment, so it allows
+  // unmuted by default. Same for when showing a lobby, as users can adjust
+  // their settings there. Additionally, if the call intent is "audio", we
+  // disable video by default.
   return {
     audioEnabled: true,
     videoEnabled: callIntent != "audio",
diff --git a/src/state/useMuteStates.ts b/src/state/useMuteStates.ts
new file mode 100644
index 000000000..908a6b182
--- /dev/null
+++ b/src/state/useMuteStates.ts
@@ -0,0 +1,51 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useEffect, useState } from "react";
+
+import { MuteStates } from "./MuteStates";
+import { ObservableScope } from "./ObservableScope";
+import { calculateInitialMuteState } from "./initialMuteState";
+import { useMediaDevices } from "../MediaDevicesContext";
+import { useHostBridge } from "../HostBridge";
+import { useUrlParams } from "../UrlParams";
+
+/**
+ * Audio and video mute state, kept in step with the host.
+ *
+ * `null` until the media devices have been looked at, since what the user
+ * starts muted depends on what they have.
+ *
+ * Whoever shows the user their own camera owns one of these. Note there should
+ * only ever be one alive at a time: each reports the user's mute state to the
+ * host, so two would have them talking over each other.
+ */
+export function useMuteStates(): MuteStates | null {
+  const urlParams = useUrlParams();
+  const hostBridge = useHostBridge();
+  const devices = useMediaDevices();
+  const [muteStates, setMuteStates] = useState<MuteStates | null>(null);
+
+  useEffect(() => {
+    const scope = new ObservableScope();
+    setMuteStates(
+      new MuteStates(
+        scope,
+        devices,
+        calculateInitialMuteState(
+          urlParams.skipLobby,
+          urlParams.callIntent,
+          hostBridge.allowJoinUnmutedViaIntent,
+        ),
+        hostBridge,
+      ),
+    );
+    return (): void => scope.end();
+  }, [devices, urlParams, hostBridge]);
+
+  return muteStates;
+}
diff --git a/src/tile/SpotlightTile.tsx b/src/tile/SpotlightTile.tsx
index 036e044fe..97e1f4a62 100644
--- a/src/tile/SpotlightTile.tsx
+++ b/src/tile/SpotlightTile.tsx
@@ -54,6 +54,7 @@ import { Slider } from "../Slider";
 import { platform } from "../Platform";
 import { type RingingMediaViewModel } from "../state/media/RingingMediaViewModel";
 import { RingingStatus } from "./RingingStatus";
+import { useRootElement } from "../RootElementContext";
 
 interface SpotlightItemBaseProps {
   ref?: Ref<HTMLDivElement>;
@@ -414,6 +415,7 @@ export const SpotlightTile: FC<Props> = ({
   style,
 }) => {
   const { t } = useTranslation();
+  const rootElement = useRootElement();
   const [ourRef, root$] = useObservableRef<HTMLDivElement | null>(null);
   const ref = useMergedRefs(ourRef, theirRef);
   const maximised = useBehavior(vm.maximised$);
@@ -428,24 +430,22 @@ export const SpotlightTile: FC<Props> = ({
   const canGoToNext = visibleIndex !== -1 && visibleIndex < media.length - 1;
 
   const isFullscreen = useCallback((): boolean => {
-    const rootElement = document.body;
     if (rootElement && document.fullscreenElement) return true;
     return false;
-  }, []);
+  }, [rootElement]);
 
   const FullScreenIcon = isFullscreen()
     ? FullScreenMinimiseIcon
     : FullScreenMaximiseIcon;
 
   const onToggleFullscreen = useCallback(() => {
-    const rootElement = document.body;
     if (!rootElement) return;
     if (isFullscreen()) {
       void document?.exitFullscreen();
     } else {
       void rootElement.requestFullscreen();
     }
-  }, [isFullscreen]);
+  }, [isFullscreen, rootElement]);
 
   // To keep track of which item is visible, we need an intersection observer
   // hooked up to the root element and the items. Because the items will run
diff --git a/src/useCallViewKeyboardShortcuts.test.tsx b/src/useCallViewKeyboardShortcuts.test.tsx
index b002c23e9..fddba5039 100644
--- a/src/useCallViewKeyboardShortcuts.test.tsx
+++ b/src/useCallViewKeyboardShortcuts.test.tsx
@@ -18,6 +18,7 @@ import {
   ReactionsRowSize,
 } from "./reactions";
 import { type Controls } from "./controls";
+import { RootElementProvider } from "./RootElementContext";
 
 // Test Explanation:
 // - The main objective is to test `useCallViewKeyboardShortcuts`.
@@ -48,10 +49,11 @@ const TestComponent: FC<TestComponentProps> = ({
   );
   return (
     <>
-      <div id={initialModalOpen ? "root" : undefined}>
+      <div>
         <Button onClick={onButtonClick}>TEST</Button>
       </div>
-      {/*// modal lives outside of the root*/}
+      {/* A dialog, which is what claims key presses for itself; where it
+      lives in the DOM does not matter */}
       {modalOpen && (
         <dialog
           open
@@ -165,7 +167,7 @@ test("unmuting happens in place of the default action", async () => {
   // container element that can be interactive and receive focus / keydown
   // events. <video> is kind of a weird choice, but it'll do the job.
   render(
-    <div id="root">
+    <div>
       <video
         tabIndex={0}
         onKeyDown={(e) => defaultPrevented(e.isDefaultPrevented())}
@@ -210,3 +212,58 @@ test("escape button does not trigger back if sth else is focused", async () => {
   await user.keyboard("[Escape]");
   expect(window.controls.onBackButtonPressed).toHaveBeenCalled();
 });
+
+test("typing in a text field is not a shortcut", async () => {
+  const user = userEvent.setup();
+  const toggleHandRaised = vi.fn();
+  const { getByRole } = render(
+    <>
+      <input type="text" aria-label="Name" />
+      <TestComponent toggleHandRaised={toggleHandRaised} />
+    </>,
+  );
+
+  getByRole("textbox", { name: "Name" }).focus();
+  await user.keyboard("h");
+  expect(toggleHandRaised).not.toHaveBeenCalled();
+});
+
+/**
+ * Element Call embedded in a host's page: the root is a container, with the
+ * rest of the page around it.
+ */
+const Embedded: FC<{ toggleHandRaised: () => void }> = ({
+  toggleHandRaised,
+}) => {
+  const [root, setRoot] = useState<HTMLDivElement | null>(null);
+  return (
+    <>
+      <button>Host button</button>
+      <div ref={setRoot} data-testid="root">
+        {root !== null && (
+          <RootElementProvider value={root}>
+            <TestComponent toggleHandRaised={toggleHandRaised} />
+          </RootElementProvider>
+        )}
+      </div>
+    </>
+  );
+};
+
+test("only hears keys pressed within its root element", async () => {
+  const user = userEvent.setup();
+  const toggleHandRaised = vi.fn();
+  const { getByRole } = render(
+    <Embedded toggleHandRaised={toggleHandRaised} />,
+  );
+
+  // Focus on the host's page: none of Element Call's business
+  getByRole("button", { name: "Host button" }).focus();
+  await user.keyboard("h");
+  expect(toggleHandRaised).not.toHaveBeenCalled();
+
+  // Focus inside the root: a shortcut
+  getByRole("button", { name: "TEST" }).focus();
+  await user.keyboard("h");
+  expect(toggleHandRaised).toHaveBeenCalledOnce();
+});
diff --git a/src/useCallViewKeyboardShortcuts.ts b/src/useCallViewKeyboardShortcuts.ts
index 9022d22fa..b95f643b4 100644
--- a/src/useCallViewKeyboardShortcuts.ts
+++ b/src/useCallViewKeyboardShortcuts.ts
@@ -9,6 +9,7 @@ import { useCallback, useMemo, useRef } from "react";
 import { logger } from "matrix-js-sdk/lib/logger";
 
 import { useEventTarget } from "./useEvents";
+import { useRootElement } from "./RootElementContext";
 import {
   type ReactionOption,
   ReactionSet,
@@ -16,28 +17,37 @@ import {
 } from "./reactions";
 
 /**
- * Determines whether focus is in the same part of the tree as the given
- * element (specifically, if the element or an ancestor of it is focused).
+ * Whether what has focus is something a key press belongs to, rather than
+ * being free for a shortcut: a dialog (the settings, the invite modal, the
+ * reaction picker), or anything the user types into.
+ *
+ * Judged by what the focused element is, not by where it sits in the DOM:
+ * Element Call's modals are portalled to whatever it treats as its root, which
+ * is the body for the standalone app but a container inside the host's page
+ * for the component.
  */
-const mayReceiveKeyEvents = (): boolean => {
-  const root = document.getElementById("root");
-  if (root === null) {
-    logger.warn(
-      "[mayReceiveKeyEvents] Root element not found, always allow keyboard shortcuts (m,v,esc...)",
-    );
-    return true;
-  }
-  const focusElement = document.activeElement;
-  const nothingInFocus = focusElement === null;
-  const focusOnBody = focusElement === document.body;
-  const noPrimaryFocus =
-    nothingInFocus || root.contains(focusElement) || focusOnBody;
+const focusIsClaimed = (): boolean => {
+  const active = document.activeElement;
+  if (active === null || active === document.body) return false;
+  if (active.closest("dialog, [role='dialog']") !== null) return true;
+  return isTextEntry(active);
+};
 
-  logger.warn(
-    `[mayReceiveKeyEvents] nothingInFocus ${nothingInFocus}, focusOnBody ${focusOnBody}, noPrimaryFocus ${noPrimaryFocus}`,
-  );
-  // Only if we do not have a primary focus we allow keyboard shortcut events.
-  return noPrimaryFocus;
+const textInputTypes = new Set([
+  "text",
+  "search",
+  "email",
+  "url",
+  "password",
+  "number",
+  "tel",
+]);
+
+const isTextEntry = (element: Element): boolean => {
+  if (element instanceof HTMLTextAreaElement) return true;
+  if (element instanceof HTMLInputElement)
+    return textInputTypes.has(element.type);
+  return element instanceof HTMLElement && element.isContentEditable;
 };
 
 /**
@@ -54,10 +64,15 @@ const KeyToReactionMap: Record<string, ReactionOption> = Object.fromEntries(
 );
 
 /**
- * This hook sets up gloabl keyboard shortcuts. It will filter for keyboard presses that should be ignored due to user
- * currently focussing on a modal.
- * This is achieved by using the fact, that all modal inputs are outside the #root element and use react portals to get rendered.
- * The following shortcuts are auspported (optional):
+ * Sets up the call's keyboard shortcuts.
+ *
+ * They are listened for on the element Element Call treats as its root — the
+ * page, standalone, or the container a host mounted it in — so that a key
+ * pressed anywhere else on a host's page is none of Element Call's business,
+ * and two Element Calls on one page each only hear their own. Key presses that
+ * belong to something else — a dialog, a text field — are left alone.
+ *
+ * The following shortcuts are supported (optional):
  * @param toggleAudio - triggered on (m)
  * @param toggleVideo - triggered on (v)
  * @param setAudioEnabled - push to talk behavior controlled via (space)
@@ -76,17 +91,19 @@ export function useCallViewKeyboardShortcuts(
   toggleHandRaised: (() => void) | null,
 ): void {
   const spacebarHeld = useRef(false);
+  const rootElement = useRootElement();
 
-  // These event handlers are set on the window because we want users to be able
-  // to trigger them without going to the trouble of focusing something
+  // Listened for on the root rather than on what has focus, so that the user
+  // need not focus anything in particular for a shortcut to work: a key pressed
+  // with nothing focused reaches the body, which is the root standalone.
 
   useEventTarget(
-    window,
+    rootElement,
     "keydown",
     useCallback(
       (event: KeyboardEvent) => {
         logger.info("Keydown event", event);
-        if (!mayReceiveKeyEvents()) return;
+        if (focusIsClaimed()) return;
         if (event.altKey || event.ctrlKey || event.metaKey || event.shiftKey)
           return;
 
@@ -121,18 +138,18 @@ export function useCallViewKeyboardShortcuts(
         toggleHandRaised,
       ],
     ),
-    // Because this is set on the window, to prevent shortcuts from activating
+    // Because this is set on an ancestor, to prevent shortcuts from activating
     // another event callback at the same time, we need to preventDefault
     // *before* child elements receive the event by using capture mode
     useMemo(() => ({ capture: true }), []),
   );
 
   useEventTarget(
-    window,
+    rootElement,
     "keyup",
     useCallback(
       (event: KeyboardEvent) => {
-        if (!mayReceiveKeyEvents() || !mayReceiveSpaceKeyEvents()) return;
+        if (focusIsClaimed() || !mayReceiveSpaceKeyEvents()) return;
         if (event.key === " ") {
           spacebarHeld.current = false;
           setAudioEnabled?.(false);
@@ -142,6 +159,7 @@ export function useCallViewKeyboardShortcuts(
     ),
   );
 
+  // Losing the window is what releases a held spacebar, wherever we are in it
   useEventTarget(
     window,
     "blur",
diff --git a/src/useRootSize.test.tsx b/src/useRootSize.test.tsx
new file mode 100644
index 000000000..6afa7adcd
--- /dev/null
+++ b/src/useRootSize.test.tsx
@@ -0,0 +1,115 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { act, renderHook } from "@testing-library/react";
+import { createElement, type FC, type PropsWithChildren } from "react";
+import { afterEach, beforeEach, describe, expect, test, vi } from "vitest";
+
+import { useRootSizeMatches } from "./useRootSize";
+import { RootElementProvider } from "./RootElementContext";
+
+/** A ResizeObserver the test fires itself. jsdom does not ship one. */
+class MockResizeObserver {
+  public static instances: MockResizeObserver[] = [];
+
+  public constructor(private readonly callback: ResizeObserverCallback) {
+    MockResizeObserver.instances.push(this);
+  }
+
+  public observe(): void {
+    this.fire();
+  }
+
+  public unobserve(): void {}
+
+  public disconnect(): void {}
+
+  public fire(): void {
+    this.callback([], this as unknown as ResizeObserver);
+  }
+}
+
+describe("useRootSizeMatches", () => {
+  const originalResizeObserver = window.ResizeObserver;
+  let root: HTMLDivElement;
+  let size: { width: number; height: number };
+  let Wrapper: FC<PropsWithChildren>;
+
+  beforeEach(() => {
+    MockResizeObserver.instances = [];
+    window.ResizeObserver =
+      MockResizeObserver as unknown as typeof ResizeObserver;
+    size = { width: 800, height: 600 };
+    root = document.createElement("div");
+    Object.defineProperty(root, "clientWidth", { get: () => size.width });
+    Object.defineProperty(root, "clientHeight", { get: () => size.height });
+    Wrapper = ({ children }) =>
+      createElement(RootElementProvider, { value: root }, children);
+  });
+
+  afterEach(() => {
+    window.ResizeObserver = originalResizeObserver;
+  });
+
+  const resize = (to: { width: number; height: number }): void => {
+    size = to;
+    act(() => {
+      for (const observer of MockResizeObserver.instances) observer.fire();
+    });
+  };
+
+  test("answers for the root's current size straight away", () => {
+    const { result } = renderHook(
+      () => useRootSizeMatches(({ width }) => width <= 550),
+      { wrapper: Wrapper },
+    );
+    expect(result.current).toBe(false);
+  });
+
+  test("follows the root as it is resized", () => {
+    const { result } = renderHook(
+      () => useRootSizeMatches(({ width }) => width <= 550),
+      { wrapper: Wrapper },
+    );
+
+    resize({ width: 300, height: 600 });
+    expect(result.current).toBe(true);
+
+    resize({ width: 900, height: 600 });
+    expect(result.current).toBe(false);
+  });
+
+  test("only re-renders when the answer changes", () => {
+    const renders = vi.fn();
+    renderHook(
+      () => {
+        renders();
+        return useRootSizeMatches(({ height }) => height <= 500);
+      },
+      { wrapper: Wrapper },
+    );
+    const before = renders.mock.calls.length;
+
+    // Still tall enough either way
+    resize({ width: 800, height: 700 });
+    resize({ width: 500, height: 650 });
+    expect(renders.mock.calls.length).toBe(before);
+
+    resize({ width: 500, height: 400 });
+    expect(renders.mock.calls.length).toBe(before + 1);
+  });
+
+  test("keeps one subscription across renders with an inline predicate", () => {
+    const { rerender } = renderHook(
+      () => useRootSizeMatches(({ width }) => width <= 550),
+      { wrapper: Wrapper },
+    );
+    rerender();
+    rerender();
+    expect(MockResizeObserver.instances).toHaveLength(1);
+  });
+});
diff --git a/src/useRootSize.ts b/src/useRootSize.ts
new file mode 100644
index 000000000..9db159a0d
--- /dev/null
+++ b/src/useRootSize.ts
@@ -0,0 +1,50 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useEffect, useState } from "react";
+import { distinctUntilChanged, map } from "rxjs";
+
+import { useRootElement } from "./RootElementContext";
+import { useLatest } from "./useLatest";
+import { type ElementSize, observeElementSize$ } from "./utils/elementSize";
+
+/**
+ * Whether the space Element Call is drawn in satisfies a condition on its
+ * size: the counterpart of {@link useMediaQuery} for the container rather than
+ * the viewport, and of the `@container element-call` queries in the
+ * stylesheets. The two are the same thing standalone, where the root is the
+ * page; for a component in a corner of a host's page they are not, and it is
+ * the corner that matters.
+ *
+ * Re-renders only when the answer changes, not on every pixel of resize.
+ */
+export function useRootSizeMatches(
+  matches: (size: ElementSize) => boolean,
+): boolean {
+  const rootElement = useRootElement();
+  // The latest predicate, so that an inline arrow does not resubscribe on
+  // every render
+  const latestMatches = useLatest(matches);
+  const [result, setResult] = useState(() =>
+    matches({
+      width: rootElement.clientWidth,
+      height: rootElement.clientHeight,
+    }),
+  );
+
+  useEffect(() => {
+    const subscription = observeElementSize$(rootElement)
+      .pipe(
+        map((size) => latestMatches.current(size)),
+        distinctUntilChanged(),
+      )
+      .subscribe(setResult);
+    return (): void => subscription.unsubscribe();
+  }, [rootElement, latestMatches]);
+
+  return result;
+}
diff --git a/src/useStableValue.test.ts b/src/useStableValue.test.ts
new file mode 100644
index 000000000..8759cbafd
--- /dev/null
+++ b/src/useStableValue.test.ts
@@ -0,0 +1,64 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { renderHook } from "@testing-library/react";
+import { describe, expect, test } from "vitest";
+
+import { useStableValue } from "./useStableValue";
+
+describe("useStableValue", () => {
+  test("keeps the first identity while the contents stay equal", () => {
+    const first = { skipLobby: true, fonts: ["Inter"] };
+    const { result, rerender } = renderHook(
+      ({ value }) => useStableValue(value),
+      { initialProps: { value: first } },
+    );
+    expect(result.current).toBe(first);
+
+    rerender({ value: { skipLobby: true, fonts: ["Inter"] } });
+    expect(result.current).toBe(first);
+  });
+
+  test("takes the new identity once the contents change", () => {
+    const first = { skipLobby: true };
+    const second = { skipLobby: false };
+    const { result, rerender } = renderHook(
+      ({ value }) => useStableValue(value),
+      { initialProps: { value: first } },
+    );
+
+    rerender({ value: second });
+    expect(result.current).toBe(second);
+
+    // And that identity is then the stable one
+    rerender({ value: { skipLobby: false } });
+    expect(result.current).toBe(second);
+  });
+
+  test("handles undefined, for an optional prop left out", () => {
+    const { result, rerender } = renderHook(
+      ({ value }) => useStableValue(value),
+      { initialProps: { value: undefined as { a: number } | undefined } },
+    );
+    expect(result.current).toBeUndefined();
+
+    const given = { a: 1 };
+    rerender({ value: given });
+    expect(result.current).toBe(given);
+  });
+
+  test("accepts its own notion of equality", () => {
+    const first = { id: 1, label: "a" };
+    const { result, rerender } = renderHook(
+      ({ value }) => useStableValue(value, (a, b) => a.id === b.id),
+      { initialProps: { value: first } },
+    );
+
+    rerender({ value: { id: 1, label: "b" } });
+    expect(result.current).toBe(first);
+  });
+});
diff --git a/src/useStableValue.ts b/src/useStableValue.ts
new file mode 100644
index 000000000..890832166
--- /dev/null
+++ b/src/useStableValue.ts
@@ -0,0 +1,29 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useState } from "react";
+import { isEqual } from "lodash-es";
+
+/**
+ * Returns a value whose identity only changes when its contents do.
+ *
+ * For a prop that a caller is likely to write inline — an options object, say
+ * — so that a fresh but equal object on every render does not restart whatever
+ * depends on it. Deep equality by default.
+ */
+export function useStableValue<T>(
+  value: T,
+  equals: (a: T, b: T) => boolean = isEqual,
+): T {
+  const [stable, setStable] = useState(value);
+  if (equals(stable, value)) return stable;
+  // Setting state during render makes React re-run this render immediately
+  // with the new state, at which point the two are identical and the stored
+  // one is returned — so the identity handed out is consistent.
+  setStable(value);
+  return value;
+}
diff --git a/src/useTheme.test.ts b/src/useTheme.test.ts
index 6e4714626..fe0cbffb3 100644
--- a/src/useTheme.test.ts
+++ b/src/useTheme.test.ts
@@ -6,6 +6,8 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { act, renderHook } from "@testing-library/react";
+import { createElement, type FC, type PropsWithChildren } from "react";
+import { Subject } from "rxjs";
 import {
   afterEach,
   beforeEach,
@@ -15,31 +17,36 @@ import {
   test,
   vi,
 } from "vitest";
-import EventEmitter from "events";
-import { WidgetApiToWidgetAction } from "matrix-widget-api";
 
 import { useTheme } from "./useTheme";
-import { getUrlParams } from "./UrlParams";
-import { widget } from "./widget";
+import { platform } from "./Platform";
+import { useUrlParams } from "./UrlParams";
+import {
+  type HostBridge,
+  HostBridgeProvider,
+  type HostRequest,
+  nullHostBridge,
+} from "./HostBridge";
 
-vi.mock("./UrlParams", () => ({ getUrlParams: vi.fn() }));
-vi.mock("./widget", () => ({
-  widget: {
-    api: { transport: { reply: vi.fn() } },
-    lazyActions: new EventEmitter(),
-  },
-}));
+vi.mock("./UrlParams", () => ({ useUrlParams: vi.fn() }));
 
 describe("useTheme", () => {
   let originalClassList: DOMTokenList;
+  let themeChange$: Subject<HostRequest<{ name?: string }>>;
+  let wrapper: FC<PropsWithChildren>;
+
   beforeEach(() => {
+    themeChange$ = new Subject();
+    const hostBridge: HostBridge = { ...nullHostBridge, themeChange$ };
+    wrapper = ({ children }) =>
+      createElement(HostBridgeProvider, { value: hostBridge }, children);
     // Save the original classList to setup spies
     originalClassList = document.body.classList;
 
     vi.spyOn(originalClassList, "add");
     vi.spyOn(originalClassList, "remove");
     vi.spyOn(originalClassList, "item").mockReturnValue(null);
-    (getUrlParams as Mock).mockReturnValue({ theme: "dark" });
+    (useUrlParams as Mock).mockReturnValue({ theme: "dark" });
   });
 
   afterEach(() => {
@@ -53,9 +60,9 @@ describe("useTheme", () => {
     { setTheme: "light-high-contrast", add: ["cpd-theme-light-hc"] },
   ])("apply procedure", ({ setTheme, add }) => {
     test(`should apply ${add[0]} theme when ${setTheme} theme is specified`, () => {
-      (getUrlParams as Mock).mockReturnValue({ theme: setTheme });
+      (useUrlParams as Mock).mockReturnValue({ theme: setTheme });
 
-      renderHook(() => useTheme());
+      renderHook(() => useTheme(), { wrapper });
 
       expect(originalClassList.remove).toHaveBeenCalledWith(
         "cpd-theme-light",
@@ -71,7 +78,7 @@ describe("useTheme", () => {
     // Simulate a previous theme
     originalClassList.item = vi.fn().mockReturnValue("cpd-theme-dark");
 
-    renderHook(() => useTheme());
+    renderHook(() => useTheme(), { wrapper });
 
     expect(document.body.classList.add).not.toHaveBeenCalledWith(
       "cpd-theme-dark",
@@ -82,18 +89,27 @@ describe("useTheme", () => {
     expect(originalClassList.add).not.toHaveBeenCalled();
   });
 
-  test("theme changes in response to widget actions", async () => {
-    renderHook(() => useTheme());
+  test("marks the element as Element Call's root, for the stylesheets", () => {
+    renderHook(() => useTheme(), { wrapper });
+
+    // The stylesheets find the root by this rather than by naming `body`, so
+    // that they still apply when Element Call is mounted into a container
+    expect(document.body.hasAttribute("data-element-call-root")).toBe(true);
+  });
+
+  test("records the platform on the root, for the stylesheets", () => {
+    renderHook(() => useTheme(), { wrapper });
+
+    expect(document.body.getAttribute("data-platform")).toBe(platform);
+  });
+
+  test("theme changes in response to host requests", () => {
+    renderHook(() => useTheme(), { wrapper });
 
     expect(originalClassList.add).toHaveBeenCalledWith("cpd-theme-dark");
-    await act(() =>
-      widget!.lazyActions.emit(
-        WidgetApiToWidgetAction.ThemeChange,
-        new CustomEvent(WidgetApiToWidgetAction.ThemeChange, {
-          detail: { data: { name: "light" } },
-        }),
-      ),
-    );
+    const reply = vi.fn();
+    act(() => themeChange$.next({ data: { name: "light" }, reply }));
+    expect(reply).toHaveBeenCalledOnce();
     expect(originalClassList.remove).toHaveBeenCalledWith(
       "cpd-theme-light",
       "cpd-theme-dark",
diff --git a/src/useTheme.ts b/src/useTheme.ts
index e992aee7b..86a6f63fd 100644
--- a/src/useTheme.ts
+++ b/src/useTheme.ts
@@ -6,38 +6,36 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { useEffect, useLayoutEffect, useRef, useState } from "react";
-import { WidgetApiToWidgetAction } from "matrix-widget-api";
-import { type IThemeChangeActionRequest } from "matrix-widget-api";
 
-import { getUrlParams } from "./UrlParams";
-import { widget } from "./widget";
+import { useUrlParams } from "./UrlParams";
+import { useRootElement } from "./RootElementContext";
+import { platform } from "./Platform";
+import { useHostBridge } from "./HostBridge";
 
 export const useTheme = (): void => {
-  const [requestedTheme, setRequestedTheme] = useState(
-    () => getUrlParams().theme,
-  );
-  const previousTheme = useRef<string | null>(document.body.classList.item(0));
+  const rootElement = useRootElement();
+  const hostBridge = useHostBridge();
+  const { theme } = useUrlParams();
+  const [requestedTheme, setRequestedTheme] = useState(theme);
+  const previousTheme = useRef<string | null>(rootElement.classList.item(0));
 
   useEffect(() => {
-    if (widget) {
-      const onThemeChange = (
-        ev: CustomEvent<IThemeChangeActionRequest>,
-      ): void => {
-        ev.preventDefault();
-        if ("name" in ev.detail.data && typeof ev.detail.data.name === "string")
-          setRequestedTheme(ev.detail.data.name);
-        widget!.api.transport.reply(ev.detail, {});
-      };
+    const subscription = hostBridge.themeChange$.subscribe(
+      ({ data, reply }) => {
+        if (typeof data.name === "string") setRequestedTheme(data.name);
+        reply();
+      },
+    );
+    return (): void => subscription.unsubscribe();
+  }, [hostBridge]);
 
-      widget.lazyActions.on(WidgetApiToWidgetAction.ThemeChange, onThemeChange);
-      return (): void => {
-        widget!.lazyActions.off(
-          WidgetApiToWidgetAction.ThemeChange,
-          onThemeChange,
-        );
-      };
-    }
-  }, []);
+  // Mark the element as Element Call's root and record the platform on it, so
+  // that the stylesheets can find both without naming `body`. A layout effect,
+  // like the theme below, so that it lands before anything is painted.
+  useLayoutEffect(() => {
+    rootElement.setAttribute("data-element-call-root", "");
+    rootElement.setAttribute("data-platform", platform);
+  }, [rootElement]);
 
   useLayoutEffect(() => {
     // If no theme has been explicitly requested we default to dark
@@ -47,15 +45,15 @@ export const useTheme = (): void => {
       : "";
     const themeString = "cpd-theme-" + theme + themeHighContrast;
     if (themeString !== previousTheme.current) {
-      document.body.classList.remove(
+      rootElement.classList.remove(
         "cpd-theme-light",
         "cpd-theme-dark",
         "cpd-theme-light-hc",
         "cpd-theme-dark-hc",
       );
-      document.body.classList.add(themeString);
+      rootElement.classList.add(themeString);
       previousTheme.current = themeString;
     }
-    document.body.classList.remove("no-theme");
-  }, [previousTheme, requestedTheme]);
+    rootElement.classList.remove("no-theme");
+  }, [previousTheme, requestedTheme, rootElement]);
 };
diff --git a/src/utils/elementSize.test.ts b/src/utils/elementSize.test.ts
new file mode 100644
index 000000000..854da6f1d
--- /dev/null
+++ b/src/utils/elementSize.test.ts
@@ -0,0 +1,104 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { observeElementSize$ } from "./elementSize";
+
+/**
+ * A ResizeObserver whose notifications the test triggers itself, and which
+ * keeps track of what it is watching. jsdom does not ship one.
+ */
+class MockResizeObserver {
+  public static instances: MockResizeObserver[] = [];
+  public observed: Element[] = [];
+  public disconnected = false;
+
+  public constructor(private readonly callback: ResizeObserverCallback) {
+    MockResizeObserver.instances.push(this);
+  }
+
+  public observe(element: Element): void {
+    this.observed.push(element);
+    // Real observers report the initial size once observation starts
+    this.fire();
+  }
+
+  public unobserve(): void {}
+
+  public disconnect(): void {
+    this.disconnected = true;
+  }
+
+  public fire(): void {
+    this.callback([], this as unknown as ResizeObserver);
+  }
+}
+
+describe("observeElementSize$", () => {
+  const originalResizeObserver = window.ResizeObserver;
+  let element: HTMLDivElement;
+  let size: { width: number; height: number };
+
+  beforeEach(() => {
+    MockResizeObserver.instances = [];
+    window.ResizeObserver =
+      MockResizeObserver as unknown as typeof ResizeObserver;
+    // jsdom does no layout, so the element reports whatever we say it does
+    size = { width: 800, height: 600 };
+    element = document.createElement("div");
+    Object.defineProperty(element, "clientWidth", { get: () => size.width });
+    Object.defineProperty(element, "clientHeight", { get: () => size.height });
+  });
+
+  afterEach(() => {
+    window.ResizeObserver = originalResizeObserver;
+  });
+
+  it("emits the current size synchronously on subscription", () => {
+    const next = vi.fn();
+    observeElementSize$(element).subscribe(next);
+    expect(next).toHaveBeenCalledTimes(1);
+    expect(next).toHaveBeenCalledWith({ width: 800, height: 600 });
+    expect(MockResizeObserver.instances[0].observed).toEqual([element]);
+  });
+
+  it("emits again whenever the element is resized", () => {
+    const next = vi.fn();
+    observeElementSize$(element).subscribe(next);
+    const [observer] = MockResizeObserver.instances;
+
+    size = { width: 300, height: 300 };
+    observer.fire();
+    size = { width: 1000, height: 700 };
+    observer.fire();
+
+    expect(next.mock.calls.map(([s]) => s)).toEqual([
+      { width: 800, height: 600 },
+      { width: 300, height: 300 },
+      { width: 1000, height: 700 },
+    ]);
+  });
+
+  it("does not repeat a size that has not changed", () => {
+    const next = vi.fn();
+    observeElementSize$(element).subscribe(next);
+    // The initial report the observer makes on observe() carried the same size
+    // as the synchronous measurement, and so did not count
+    expect(next).toHaveBeenCalledTimes(1);
+    MockResizeObserver.instances[0].fire();
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it("stops observing when unsubscribed", () => {
+    const subscription = observeElementSize$(element).subscribe();
+    const [observer] = MockResizeObserver.instances;
+    expect(observer.disconnected).toBe(false);
+    subscription.unsubscribe();
+    expect(observer.disconnected).toBe(true);
+  });
+});
diff --git a/src/utils/elementSize.ts b/src/utils/elementSize.ts
new file mode 100644
index 000000000..c2d5e921b
--- /dev/null
+++ b/src/utils/elementSize.ts
@@ -0,0 +1,42 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { Observable, distinctUntilChanged } from "rxjs";
+
+export interface ElementSize {
+  width: number;
+  height: number;
+}
+
+/**
+ * Observes the size of an element, starting with the size it currently has and
+ * following it through every change for as long as the subscription lasts.
+ *
+ * Measured with `clientWidth`/`clientHeight`, so borders, scrollbars and any
+ * transforms a host might animate the element with are left out: this is the
+ * space there is to draw in, not where the element happens to be painted.
+ */
+export function observeElementSize$(element: Element): Observable<ElementSize> {
+  return new Observable<ElementSize>((subscriber) => {
+    const measure = (): void =>
+      subscriber.next({
+        width: element.clientWidth,
+        height: element.clientHeight,
+      });
+    // Synchronously, so that a Behavior built on this has an initial value
+    measure();
+    const observer = new ResizeObserver(measure);
+    observer.observe(element);
+    return (): void => observer.disconnect();
+  }).pipe(
+    // A ResizeObserver reports once on observe(), which repeats the first
+    // measurement above, and again for changes to dimensions we do not read
+    distinctUntilChanged(
+      (a, b) => a.width === b.width && a.height === b.height,
+    ),
+  );
+}
diff --git a/src/utils/errors.test.ts b/src/utils/errors.test.ts
new file mode 100644
index 000000000..306aa3cf8
--- /dev/null
+++ b/src/utils/errors.test.ts
@@ -0,0 +1,62 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test } from "vitest";
+
+import {
+  ErrorCategory,
+  ErrorCode,
+  FailToStartLivekitConnection,
+  MembershipManagerError,
+  NoMatrix2AuthorizationService,
+  SFURoomCreationRestrictedError,
+} from "./errors";
+
+// These errors take their wording from Element Call's own i18next instance
+// rather than the global one, so each needs to come out translated rather than
+// as a raw key.
+describe("localised errors", () => {
+  test("MembershipManagerError describes the failure and keeps its cause", () => {
+    const cause = new Error("the underlying problem");
+    const error = new MembershipManagerError(cause);
+
+    expect(error.code).toBe(ErrorCode.INTERNAL_MEMBERSHIP_MANAGER);
+    expect(error.category).toBe(ErrorCategory.SYSTEM_FAILURE);
+    expect(error.localisedTitle).not.toContain("error.");
+    expect(error.localisedMessage).not.toContain("error.");
+    expect(error.cause).toBe(cause);
+  });
+
+  test("NoMatrix2AuthorizationService is a configuration problem", () => {
+    const cause = new Error("404");
+    const error = new NoMatrix2AuthorizationService(cause);
+
+    expect(error.code).toBe(ErrorCode.NO_MATRIX_2_AUTHORIZATION_SERVICE);
+    expect(error.category).toBe(ErrorCategory.CONFIGURATION_ISSUE);
+    expect(error.localisedTitle).not.toContain("error.");
+    expect(error.localisedMessage).not.toContain("error.");
+    expect(error.cause).toBe(cause);
+  });
+
+  test("FailToStartLivekitConnection passes its detail through", () => {
+    const error = new FailToStartLivekitConnection("could not publish");
+
+    expect(error.code).toBe(ErrorCode.FAILED_TO_START_LIVEKIT);
+    expect(error.category).toBe(ErrorCategory.NETWORK_CONNECTIVITY);
+    expect(error.localisedTitle).not.toContain("error.");
+    expect(error.localisedMessage).toBe("could not publish");
+  });
+
+  test("SFURoomCreationRestrictedError explains the restriction", () => {
+    const error = new SFURoomCreationRestrictedError();
+
+    expect(error.code).toBe(ErrorCode.SFU_ERROR);
+    expect(error.category).toBe(ErrorCategory.CONFIGURATION_ISSUE);
+    expect(error.localisedTitle).not.toContain("error.");
+    expect(error.localisedMessage).not.toContain("error.");
+  });
+});
diff --git a/src/utils/errors.ts b/src/utils/errors.ts
index 0ac569278..73b904c95 100644
--- a/src/utils/errors.ts
+++ b/src/utils/errors.ts
@@ -5,10 +5,9 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { t } from "i18next";
 import { type ConnectionError } from "livekit-client";
 
-import { i18nKey } from "./i18n";
+import { i18n, i18nKey } from "./i18n";
 
 export enum ErrorCode {
   /**
@@ -78,10 +77,10 @@ export class MatrixRTCTransportMissingError extends ElementCallError {
    */
   public constructor(domain: string) {
     super(
-      t("error.call_is_not_supported"),
+      i18n.t("error.call_is_not_supported"),
       ErrorCode.MISSING_MATRIX_RTC_TRANSPORT,
       ErrorCategory.CONFIGURATION_ISSUE,
-      t("error.matrix_rtc_transport_missing", {
+      i18n.t("error.matrix_rtc_transport_missing", {
         domain,
         brand: import.meta.env.VITE_PRODUCT_NAME || "Element Call",
         errorCode: ErrorCode.MISSING_MATRIX_RTC_TRANSPORT,
@@ -97,10 +96,10 @@ export class MatrixRTCTransportMissingError extends ElementCallError {
 export class ConnectionLostError extends ElementCallError {
   public constructor() {
     super(
-      t("error.connection_lost"),
+      i18n.t("error.connection_lost"),
       ErrorCode.CONNECTION_LOST_ERROR,
       ErrorCategory.NETWORK_CONNECTIVITY,
-      t("error.connection_lost_description"),
+      i18n.t("error.connection_lost_description"),
     );
   }
 }
@@ -117,10 +116,10 @@ export class MembershipManagerError extends ElementCallError {
    */
   public constructor(error: Error) {
     super(
-      t("error.membership_manager"),
+      i18n.t("error.membership_manager"),
       ErrorCode.INTERNAL_MEMBERSHIP_MANAGER,
       ErrorCategory.SYSTEM_FAILURE,
-      t("error.membership_manager_description"),
+      i18n.t("error.membership_manager_description"),
       error,
     );
   }
@@ -134,10 +133,10 @@ export class MembershipManagerError extends ElementCallError {
 export class StickyEventsRequiredError extends ElementCallError {
   public constructor() {
     super(
-      t("error.sticky_events_required"),
+      i18n.t("error.sticky_events_required"),
       ErrorCode.STICKY_EVENTS_NOT_SUPPORTED,
       ErrorCategory.CONFIGURATION_ISSUE,
-      t("error.sticky_events_required_description"),
+      i18n.t("error.sticky_events_required_description"),
     );
   }
 }
@@ -148,10 +147,10 @@ export class StickyEventsRequiredError extends ElementCallError {
 export class E2EENotSupportedError extends ElementCallError {
   public constructor() {
     super(
-      t("error.e2ee_unsupported"),
+      i18n.t("error.e2ee_unsupported"),
       ErrorCode.E2EE_NOT_SUPPORTED,
       ErrorCategory.CLIENT_CONFIGURATION,
-      t("error.e2ee_unsupported_description"),
+      i18n.t("error.e2ee_unsupported_description"),
     );
   }
 }
@@ -166,7 +165,7 @@ export class UnknownCallError extends ElementCallError {
    */
   public constructor(error: Error) {
     super(
-      t("error.generic"),
+      i18n.t("error.generic"),
       ErrorCode.UNKNOWN_ERROR,
       ErrorCategory.UNKNOWN,
       undefined,
@@ -186,7 +185,7 @@ export class FailToGetOpenIdToken extends ElementCallError {
    */
   public constructor(error: Error) {
     super(
-      t("error.generic"),
+      i18n.t("error.generic"),
       ErrorCode.OPEN_ID_ERROR,
       ErrorCategory.CONFIGURATION_ISSUE,
       undefined,
@@ -203,10 +202,10 @@ export class NoMatrix2AuthorizationService extends ElementCallError {
    */
   public constructor(error: Error) {
     super(
-      t("error.generic"),
+      i18n.t("error.generic"),
       ErrorCode.NO_MATRIX_2_AUTHORIZATION_SERVICE,
       ErrorCategory.CONFIGURATION_ISSUE,
-      t("error.no_matrix_2_authorization_service"),
+      i18n.t("error.no_matrix_2_authorization_service"),
       // Properly set it as a cause for a better reporting on sentry
       error,
     );
@@ -223,7 +222,7 @@ export class FailToStartLivekitConnection extends ElementCallError {
    */
   public constructor(e?: string) {
     super(
-      t("error.failed_to_start_livekit"),
+      i18n.t("error.failed_to_start_livekit"),
       ErrorCode.FAILED_TO_START_LIVEKIT,
       ErrorCategory.NETWORK_CONNECTIVITY,
       e,
@@ -237,10 +236,10 @@ export class FailToStartLivekitConnection extends ElementCallError {
 export class InsufficientCapacityError extends ElementCallError {
   public constructor() {
     super(
-      t("error.insufficient_capacity"),
+      i18n.t("error.insufficient_capacity"),
       ErrorCode.INSUFFICIENT_CAPACITY_ERROR,
       ErrorCategory.UNKNOWN,
-      t("error.insufficient_capacity_description"),
+      i18n.t("error.insufficient_capacity_description"),
     );
   }
 }
@@ -252,10 +251,10 @@ export class InsufficientCapacityError extends ElementCallError {
 export class SFURoomCreationRestrictedError extends ElementCallError {
   public constructor() {
     super(
-      t("error.room_creation_restricted"),
+      i18n.t("error.room_creation_restricted"),
       ErrorCode.SFU_ERROR,
       ErrorCategory.CONFIGURATION_ISSUE,
-      t("error.room_creation_restricted_description"),
+      i18n.t("error.room_creation_restricted_description"),
     );
   }
 }
@@ -266,7 +265,7 @@ export class SFURoomCreationRestrictedError extends ElementCallError {
 export class PeerConnectionTimeoutError extends ElementCallError {
   public constructor() {
     super(
-      t("error.peer_connection_timeout"),
+      i18n.t("error.peer_connection_timeout"),
       ErrorCode.SFU_ERROR,
       ErrorCategory.NETWORK_CONNECTIVITY,
     );
@@ -283,7 +282,7 @@ export class PeerConnectionTimeoutError extends ElementCallError {
 export class LivekitConnectionError extends ElementCallError {
   public constructor(cause: ConnectionError) {
     super(
-      t("error.livekit_connection_error"),
+      i18n.t("error.livekit_connection_error"),
       ErrorCode.SFU_ERROR,
       ErrorCategory.NETWORK_CONNECTIVITY,
     );
diff --git a/src/utils/i18n.ts b/src/utils/i18n.ts
index 51bf2fb63..0796ab380 100644
--- a/src/utils/i18n.ts
+++ b/src/utils/i18n.ts
@@ -5,5 +5,37 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
+import i18next, { type i18n as I18nInstance } from "i18next";
+
 // Custom marker function to allow i18next extraction
 export const i18nKey = (key: string): string => key;
+
+/**
+ * The language a locale file under `locales/` is for, from its path as a
+ * bundler glob reports it: `../locales/zh-Hans/app.json` is for `zh-Hans`.
+ */
+export function languageOfLocalePath(path: string): string {
+  const language = path.match(/\/([^/]+)\/[^/]+\.json$/)?.[1];
+  if (language === undefined)
+    throw new Error(`Could not parse locale path ${path}`);
+  return language;
+}
+
+/**
+ * Element Call's own i18next instance.
+ *
+ * We deliberately do not use the global i18next singleton: when Element Call
+ * runs as a component inside a host application (rather than as its own page),
+ * that singleton belongs to the host, and configuring it would clobber the
+ * host's translations.
+ *
+ * It is configured by `Initializer.initBeforeReact` and made available to
+ * components via `<I18nextProvider>`; tests and stories configure it directly.
+ *
+ * Non-React code should call `i18n.t(...)` on this instance. Components should
+ * use `useTranslation()` instead, so that they re-render on a language change.
+ * Note that `t` must be reached through the instance at call time — i18next
+ * only assigns it during `init()`, so destructuring it at module scope would
+ * capture an uninitialised function.
+ */
+export const i18n: I18nInstance = i18next.createInstance();
diff --git a/src/utils/spa.ts b/src/utils/spa.ts
index e97d78101..b8e959f8b 100644
--- a/src/utils/spa.ts
+++ b/src/utils/spa.ts
@@ -40,7 +40,6 @@ export async function initSPA(
     try {
       const client = await initClient(initClientParams, true);
       return {
-        widgetApi: null,
         client,
         passwordlessUser,
       };
diff --git a/src/utils/test-viewmodel.ts b/src/utils/test-viewmodel.ts
index 974879110..9903b99f8 100644
--- a/src/utils/test-viewmodel.ts
+++ b/src/utils/test-viewmodel.ts
@@ -40,6 +40,7 @@ import { type RaisedHandInfo, type ReactionInfo } from "../reactions";
 import { constant } from "../state/Behavior";
 import { MatrixRTCMode } from "../config/ConfigOptions";
 import { createCallFooterViewModel } from "../components/CallFooterViewModel";
+import { HeaderStyle } from "../UrlParams";
 import { type FooterSnapshot } from "../components/CallFooter";
 import { type ViewModel } from "../state/ViewModel";
 import { createDeveloperSettingsTabViewModel } from "../settings/DeveloperSettingsTabViewModel";
@@ -175,6 +176,7 @@ export function getBasicCallViewModelEnvironment(
         }),
       connectionState$: constant(ConnectionState.Connected),
       matrixRTCMode: MatrixRTCMode.Compatibility,
+      windowSize$: constant({ width: 1000, height: 800 }),
       ...callViewModelOptions,
     },
     handRaisedSubject$,
@@ -187,6 +189,7 @@ export function getBasicCallViewModelEnvironment(
     muteStates,
     mediaDevices,
     "reactionId",
+    { showControls: true, header: HeaderStyle.Standard },
   );
   return {
     vm,
diff --git a/src/utils/test.ts b/src/utils/test.ts
index de74ac53e..49ae0a3f1 100644
--- a/src/utils/test.ts
+++ b/src/utils/test.ts
@@ -63,6 +63,7 @@ import { type MediaDevices } from "../state/MediaDevices";
 import { type Behavior, constant } from "../state/Behavior";
 import { ObservableScope } from "../state/ObservableScope";
 import { MuteStates } from "../state/MuteStates";
+import { nullHostBridge } from "../HostBridge";
 import {
   createLocalUserMedia,
   type LocalUserMediaViewModel,
@@ -577,10 +578,12 @@ export function mockMuteStates(
   joined$: Observable<boolean> = of(true),
 ): MuteStates {
   const observableScope = new ObservableScope();
-  return new MuteStates(observableScope, mockMediaDevices({}), {
-    audioEnabled: false,
-    videoEnabled: false,
-  });
+  return new MuteStates(
+    observableScope,
+    mockMediaDevices({}),
+    { audioEnabled: false, videoEnabled: false },
+    nullHostBridge,
+  );
 }
 
 export class MockConnection extends Connection {
diff --git a/src/vitest.setup.ts b/src/vitest.setup.ts
index be7179de4..965f42474 100644
--- a/src/vitest.setup.ts
+++ b/src/vitest.setup.ts
@@ -7,7 +7,6 @@ Please see LICENSE in the repository root for full details.
 
 import "@formatjs/intl-durationformat/polyfill.js";
 import "@formatjs/intl-segmenter/polyfill";
-import i18n from "i18next";
 import posthog from "posthog-js";
 import { initReactI18next } from "react-i18next";
 import { afterEach } from "vitest";
@@ -18,8 +17,11 @@ import "@testing-library/jest-dom/vitest";
 
 import EN from "../locales/en/app.json";
 import { Config } from "./config/Config";
+import { i18n } from "./utils/i18n";
 
-// Bare-minimum i18n config
+// Bare-minimum i18n config.
+// Unlike the app, tests register the instance as react-i18next's default rather
+// than wrapping every render in an <I18nextProvider>.
 i18n
   .use(initReactI18next)
   .init({
@@ -51,6 +53,29 @@ window.matchMedia = global.matchMedia = (): MediaQueryList =>
     removeEventListener: () => {},
   }) as Partial<MediaQueryList> as MediaQueryList;
 
+// jsdom does no layout and has no ResizeObserver. The call view observes the
+// size of its root element; this one reports nothing, so that element stays at
+// whatever size jsdom says it is unless a test says otherwise.
+window.ResizeObserver ??= class ResizeObserver {
+  public observe(): void {}
+  public unobserve(): void {}
+  public disconnect(): void {}
+};
+
+// And what jsdom says is zero, for everything — which would have every size
+// query against Element Call's root (the body, with no provider) read as a tiny
+// window. Give the body the size of a typical desktop window instead, the same
+// answer the media query mock above gives. A test that wants another size
+// supplies a root element of its own.
+for (const [property, value] of [
+  ["clientWidth", 1024],
+  ["clientHeight", 768],
+] as const)
+  Object.defineProperty(document.body, property, {
+    get: () => value,
+    configurable: true,
+  });
+
 const storage: Record<string, string> = {};
 const localStoragePolyfill = {
   getItem(key: string) {
diff --git a/src/widget.test.ts b/src/widget.test.ts
index 3618fb505..c645c3b34 100644
--- a/src/widget.test.ts
+++ b/src/widget.test.ts
@@ -9,7 +9,7 @@ import { describe, expect, vi, it, beforeEach } from "vitest";
 import { createRoomWidgetClient, EventType } from "matrix-js-sdk";
 
 import { getUrlParams } from "./UrlParams";
-import { initializeWidget, widget } from "./widget";
+import { initializeWidget } from "./widget";
 import { Config } from "./config/Config";
 import { ElementCallReactionEventType } from "./reactions";
 
@@ -42,7 +42,7 @@ beforeEach(() => {
 
 describe("widget", () => {
   it("should create an embedded client with the correct params", () => {
-    initializeWidget("ANYRTCAPP");
+    const widget = initializeWidget("ANYRTCAPP");
 
     expect(getUrlParams()).toStrictEqual({
       widgetId: "id",
diff --git a/src/widget.ts b/src/widget.ts
index af6f28b6d..b35e335bc 100644
--- a/src/widget.ts
+++ b/src/widget.ts
@@ -58,21 +58,21 @@ export interface WidgetHelpers {
 }
 
 /**
- * A point of access to the widget API, if the app is running as a widget. This
- * is initialized with `initializeWidget`. This should happen at the top level because the widget messaging
- * needs to be set up ASAP on load to ensure it doesn't miss any requests.
- */
-export let widget: WidgetHelpers | null = null;
-
-/**
- * Should be called as soon as possible on app start. (In the initilizer before react)
+ * Connects to the widget API, if Element Call is running as a widget.
+ *
+ * Should be called as soon as possible on app start (in the initializer, before
+ * React), because the widget messaging needs to be set up ASAP on load to
+ * ensure it doesn't miss any requests.
+ *
+ * @returns A point of access to the widget API, or null if Element Call is not
+ *   running as a widget.
  */
 // this needs to be a seperate call and cannot be done on import to allow us to spy on methods in here before
 // execution.
 export const initializeWidget = (
   rtcApplication: string = "m.call",
   sendRoomEvents = false,
-): void => {
+): WidgetHelpers | null => {
   try {
     const {
       widgetId,
@@ -202,14 +202,14 @@ export const initializeWidget = (
         return client;
       };
 
-      widget = { api, lazyActions, client: clientPromise() };
+      return { api, lazyActions, client: clientPromise() };
     } else {
       if (import.meta.env.MODE !== "test")
         logger.info("No widget API available");
-      widget = null;
+      return null;
     }
   } catch (e) {
     logger.warn("Continuing without the widget API", e);
-    widget = null;
+    return null;
   }
 };
diff --git a/tsconfig.json b/tsconfig.json
index 74c27025a..aba6c5ec0 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -53,7 +53,9 @@
     "./src/**/*.ts",
     "./src/**/*.tsx",
     "./playwright/**/*.ts",
-    "./sdk/**/*.ts"
+    "./sdk/**/*.ts",
+    "./component/**/*.ts",
+    "./component/**/*.tsx"
   ],
   "exclude": ["**.test.ts"]
 }
diff --git a/vite-component-dev.config.ts b/vite-component-dev.config.ts
new file mode 100644
index 000000000..2e6783820
--- /dev/null
+++ b/vite-component-dev.config.ts
@@ -0,0 +1,81 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { defineConfig, searchForWorkspaceRoot } from "vite";
+import { realpathSync } from "node:fs";
+import * as fs from "node:fs";
+
+import { vitePluginsConfig } from "./vite.config";
+import { scopeStylesToRoot } from "./component/build/scopeStylesToRoot";
+
+// Serves the harness under `component/dev`, which embeds Element Call as a
+// component the way a host application would. Development only: this is not
+// something we build or ship.
+//
+// It shares the plugins with the standalone app but not its HTML entry point,
+// since the harness has a page of its own — and it deliberately does not build
+// on the app's config, which would also bring the app's build output along.
+export default defineConfig(({ mode }) => {
+  // The crypto WASM module is imported dynamically, so Vite has to be told
+  // that reading it is legitimate — including from a linked copy, which is why
+  // the paths are resolved rather than assumed. Same as the standalone app.
+  const allow = [searchForWorkspaceRoot(process.cwd())];
+  for (const path of [
+    "node_modules/matrix-js-sdk/node_modules/@matrix-org/matrix-sdk-crypto-wasm",
+    "node_modules/@matrix-org/matrix-sdk-crypto-wasm",
+  ]) {
+    try {
+      allow.push(realpathSync(path));
+    } catch {}
+  }
+
+  return {
+    ...vitePluginsConfig({ mode, html: false }),
+    root: "component/dev",
+    // The same scoping the library build applies, so the harness shows what a
+    // host will get — including whether its own page is left alone
+    css: { postcss: { plugins: [scopeStylesToRoot()] } },
+    // So that the harness can read the same config.json the standalone app
+    // does, if the developer has written one
+    publicDir: "../../public",
+    server: {
+      host: true,
+      // One up from the standalone app's, so both can run at once — the point
+      // of the harness is to compare them
+      port: 3001,
+      fs: { allow },
+      // The same certificate the app uses, so that the harness is served from
+      // a `m.localhost` name the development homeserver's certificate covers
+      https: {
+        key: fs.readFileSync("./backend/dev_tls_m.localhost.key"),
+        cert: fs.readFileSync("./backend/dev_tls_m.localhost.crt"),
+      },
+    },
+    worker: {
+      format: "es",
+    },
+    resolve: {
+      alias: {
+        // matrix-widget-api has its transpiled lib/index.js as its entry point,
+        // which Vite for some reason refuses to work with, so we point it to
+        // src/index.ts instead
+        "matrix-widget-api": "matrix-widget-api/src/index.ts",
+      },
+      dedupe: [
+        "react",
+        "react-dom",
+        "matrix-js-sdk",
+        "react-use-measure",
+        // These packages modify the document based on some module-level global
+        // state, and don't play nicely with duplicate copies of themselves
+        // https://github.com/radix-ui/primitives/issues/1241#issuecomment-1847837850
+        "@radix-ui/react-focus-guards",
+        "@radix-ui/react-dismissable-layer",
+      ],
+    },
+  };
+});
diff --git a/vite-component.config.ts b/vite-component.config.ts
new file mode 100644
index 000000000..ae0ac1508
--- /dev/null
+++ b/vite-component.config.ts
@@ -0,0 +1,99 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { defineConfig } from "vite";
+
+import { vitePluginsConfig } from "./vite.config";
+import { scopeStylesToRoot } from "./component/build/scopeStylesToRoot";
+
+// Config for Element Call as a React component, to be imported by an
+// application embedding it rather than served as a page of its own.
+//
+// Deliberately not built on top of the full app's config, which exists to
+// produce a page and brings an HTML entry point along with it.
+export default defineConfig(({ mode }) => {
+  const base = vitePluginsConfig({ mode, html: false });
+  return {
+    ...base,
+    resolve: {
+      ...base.resolve,
+      alias: {
+        ...base.resolve?.alias,
+        // react-i18next depends on the CommonJS `use-sync-external-store/shim`, whose
+        // `require("react")` cannot be bundled against an external React: rolldown leaves a
+        // `require` shim that throws in the browser. React 18+ provides `useSyncExternalStore`
+        // itself, so point the shim at React.
+        "use-sync-external-store/shim": "react",
+      },
+    },
+    // A library has no public directory to serve. Without this the build copies
+    // whatever is in `public` — including the developer's own config.json, which
+    // is not in the repository — into the output we would publish.
+    publicDir: false,
+    // A host's document is not ours to style: everything in the stylesheet is
+    // confined to the element Element Call is mounted in
+    css: { postcss: { plugins: [scopeStylesToRoot()] } },
+    build: {
+      // Into the package directory, so that `component/package.json` describes
+      // what sits next to it and the directory can be installed as a package
+      // (see its `files` and `exports`).
+      outDir: "component/dist",
+      minify: mode === "production",
+      sourcemap: true,
+      // One stylesheet rather than one per chunk, so a host has a single file to
+      // include
+      cssCodeSplit: false,
+      lib: {
+        formats: ["es" as const],
+        entry: "./component/index.tsx",
+        fileName: "element-call",
+      },
+      rollupOptions: {
+        // The host already has these, and a second copy of any of them does not
+        // merely bloat the bundle: React would hold two sets of hooks, and the
+        // Matrix client would run two sync loops.
+        //
+        // Every subpath has to be named. Element Call reaches most of the Matrix
+        // SDK as `matrix-js-sdk/lib/…`, and a bare "matrix-js-sdk" would not
+        // catch those — while the pattern and callback forms of this option are
+        // silently ignored by the bundler, so they cannot be used to cover them.
+        // `pnpm lint:externals` reads this list and fails if the source imports
+        // one of these packages by a path it does not name; a few entries below
+        // are there only because the standalone app imports them, which costs
+        // nothing.
+        external: [
+          "react",
+          "react/jsx-runtime",
+          // Emitted by the React Compiler for every compiled component; part of React, so it must be
+          // the host's copy too (bundled, its CommonJS `require("react")` throws in the browser).
+          "react/compiler-runtime",
+          "react-dom",
+          "react-dom/client",
+          "livekit-client",
+          "matrix-js-sdk",
+          "matrix-js-sdk/lib/browser-index",
+          "matrix-js-sdk/lib/client",
+          "matrix-js-sdk/lib/crypto-api",
+          "matrix-js-sdk/lib/indexeddb-worker",
+          "matrix-js-sdk/lib/logger",
+          "matrix-js-sdk/lib/matrix",
+          "matrix-js-sdk/lib/matrixrtc",
+          "matrix-js-sdk/lib/matrixrtc/EncryptionManager",
+          "matrix-js-sdk/lib/matrixrtc/IKeyTransport",
+          "matrix-js-sdk/lib/matrixrtc/IMembershipManager",
+          "matrix-js-sdk/lib/models/relations-container",
+          "matrix-js-sdk/lib/models/room",
+          "matrix-js-sdk/lib/models/typed-event-emitter",
+          "matrix-js-sdk/lib/randomstring",
+          "matrix-js-sdk/lib/sync",
+          "matrix-js-sdk/lib/types",
+          "matrix-js-sdk/lib/utils",
+        ],
+      },
+    },
+  };
+});
diff --git a/vite.config.ts b/vite.config.ts
index 61936cfdf..678a86fab 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -26,7 +26,15 @@ import * as fs from "node:fs";
 
 export const vitePluginsConfig = ({
   mode,
-}: Pick<ConfigEnv, "mode">): UserConfig => {
+  html = true,
+}: Pick<ConfigEnv, "mode"> & {
+  /**
+   * Whether to inject Element Call's entry point into the HTML page. Builds
+   * that produce a library, or serve a page of their own, must not have this:
+   * it would pull the standalone app in alongside whatever they are building.
+   */
+  html?: boolean;
+}): UserConfig => {
   const env = loadEnv(mode, process.cwd());
   const plugins: PluginOption[] = [
     babel({
@@ -67,7 +75,7 @@ export const vitePluginsConfig = ({
     );
   }
 
-  if (!process.env.STORYBOOK && !process.env.VITEST) {
+  if (html && !process.env.STORYBOOK && !process.env.VITEST) {
     plugins.push(
       createHtmlPlugin({
         entry: "src/main.tsx",
diff --git a/vitest.config.ts b/vitest.config.ts
index c5e908e4b..81519325a 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -21,7 +21,11 @@ export default defineConfig((configEnv) =>
               css: { include: /.+/ },
               setupFiles: ["src/vitest.setup.ts"],
               environment: "jsdom",
-              include: ["src/**/*.test.ts", "src/**/*.test.tsx"],
+              include: [
+                "src/**/*.test.ts",
+                "src/**/*.test.tsx",
+                "component/**/*.test.ts",
+              ],
             },
           },
           {