Compare the component's config by value

Everything downstream of the component's params — the mute state, the
call view model and with it the media connection — is keyed on the
identity of the params object, which was memoised on the identity of
the `config` prop. A host writing `config={{ ... }}` inline, which is
the natural way to write it, therefore tore the whole call down on
every render. The harness happened to pass a constant, so nothing
noticed.

`useStableValue` hands out the same object for as long as a deep
comparison says nothing changed, so an inline config costs nothing.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

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);
+  });
+});

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;
+}