Reformat

toggleScreenSharing only had `.catch(logger.error)`, so a getDisplayMedia
request that hangs (element-call-rageshakes#17152: Element Desktop on
Windows, the user pressed the screen share button 14 times in 25 seconds
and the log shows nothing but the toggle lines and livekit-client's
"waiting for pending publication promise timed out") left the user with
a button that does nothing and us with no evidence of why.

Log when a toggle is requested and when it completes or fails, with the
elapsed time, so a hang is visible in the logs. Explicit failures other
than the user cancelling the picker show as a non-modal "Could not start
screen sharing" toast. Nothing is inferred from a toggle taking a long
time: the user may simply be choosing what to share.

docker-compose-playwright.yml

@@ -13,7 +13,7 @@ services:
       - ./backend/playwright_homeserver-othersite.yaml:/data/cfg/homeserver.yaml:Z
   element-web:
     # Pin to a SHA so that upstream cannot break our tests. Renovate handles regular updates.
-    image: ghcr.io/element-hq/element-web:develop@sha256:0332028836603e91689053f157847b4deef9342bd19e3195eeb81793b7e4046e
+    image: ghcr.io/element-hq/element-web:develop@sha256:c107ec33fa349cb5c14fd03a4e13352d64ef264416dac96d273aa07b4004171f
   element-web-1:
     # Pin to a SHA so that upstream cannot break our tests. Renovate handles regular updates.
-    image: ghcr.io/element-hq/element-web:develop@sha256:0332028836603e91689053f157847b4deef9342bd19e3195eeb81793b7e4046e
+    image: ghcr.io/element-hq/element-web:develop@sha256:c107ec33fa349cb5c14fd03a4e13352d64ef264416dac96d273aa07b4004171f

locales/en/app.json

@@ -116,6 +116,7 @@
     "peer_connection_timeout_description": "Connection to the media server timed out. Try switching to a different network or disabling your VPN. If the problem persists, see our <0>troubleshooting guide</0> or contact your server administrator.",
     "room_creation_restricted": "Failed to create call",
     "room_creation_restricted_description": "Call creation might be restricted to authorized users only. Try again later, or contact your server admin if the problem persists.",
+    "screen_share_failed": "Could not start screen sharing",
     "sticky_events_required": "Homeserver does not support Matrix 2.0 calls",
     "sticky_events_required_description": "This deployment is configured to use Matrix 2.0 call mode, but the homeserver does not advertise support for sticky events (MSC4354). Ask your server admin to upgrade, or switch the deployment to a compatible mode.",
     "unexpected_ec_error": "An unexpected error occurred (<0>Error Code:</0> <1>{{ errorCode }}</1>). Please contact your server admin."

pnpm-lock.yaml

@@ -66,7 +66,7 @@ importers:
         version: 10.1.2(react-dom@19.2.8(react@19.2.8))(react@19.2.8)
       '@rolldown/plugin-babel':
         specifier: ^0.2.3
-        version: 0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@7.29.7)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
+        version: 0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@8.0.0)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
       '@sentry/react':
         specifier: ^8.0.0
         version: 8.55.2(react@19.2.8)
@@ -138,7 +138,7 @@ importers:
         version: 10.0.1(@fontsource/inconsolata@5.3.0)(@fontsource/inter@5.3.0)(@types/react-dom@19.2.3(@types/react@19.2.17))(@types/react@19.2.17)(@vector-im/compound-design-tokens@10.2.4(@types/react@19.2.17)(react@19.2.8))(react-dom@19.2.8(react@19.2.8))(react@19.2.8)
       '@vitejs/plugin-react':
         specifier: ^6.0.2
-        version: 6.0.5(@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@7.29.7)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)))(babel-plugin-react-compiler@1.0.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
+        version: 6.0.5(@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@8.0.0)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)))(babel-plugin-react-compiler@1.0.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
       '@vitest/browser-playwright':
         specifier: ^4.1.5
         version: 4.1.10(playwright@1.62.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))(vitest@4.1.10)
@@ -192,10 +192,10 @@ importers:
         version: 1.9.2
       matrix-js-sdk:
         specifier: github:matrix-org/matrix-js-sdk#develop
-        version: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/178dc6528ebc6a15e2f6fab38410127f16b500d0
+        version: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/24929be0e741be6a5d0a7226f1c682e245263b8a
       matrix-widget-api:
         specifier: ^1.18.0
-        version: 1.18.0
+        version: 1.19.0
       node-stdlib-browser:
         specifier: ^1.3.1
         version: 1.3.1
@@ -1191,8 +1191,8 @@ packages:
       '@types/dom-mediacapture-transform': ^0.1.9
       livekit-client: ^1.12.0 || ^2.1.0
 
-  '@matrix-org/matrix-sdk-crypto-wasm@18.4.0':
-    resolution: {integrity: sha512-osxkU1DQ+05+anGHapjWyvZqdHUb94Id37gy54mCKn1Cq/D7iGT5oEUEhjp4oTnCLo4TOtI6ULJ/LHsapaIptQ==}
+  '@matrix-org/matrix-sdk-crypto-wasm@18.5.0':
+    resolution: {integrity: sha512-E826Hy1rG26LanPjtSsOiVRcVoHfSgPgj2r2Xsb5RPScpaKi9XJADQ0u3dNjRCitZPX4oyLNl1FDd5AfDlmIwQ==}
     engines: {node: '>= 18'}
 
   '@mdx-js/react@3.1.1':
@@ -3670,9 +3670,9 @@ packages:
   constants-browserify@1.0.0:
     resolution: {integrity: sha512-xFxOwqIzR/e1k1gLiWEophSCMqXcwVHIH7akf7b/vxcUeGunlj3hvZaaqxwHsTgn+IndtkQJgSztIDWeumWJDQ==}
 
-  content-type@2.0.0:
-    resolution: {integrity: sha512-j/O/d7GcZCyNl7/hwZAb606rzqkyvaDctLmckbxLzHvFBzTJHuGEdodATcP3yIRoDrLHkIATJuvzbFlp/ki2cQ==}
-    engines: {node: '>=18'}
+  content-type@3.0.0:
+    resolution: {integrity: sha512-AIi5H6p0xk5uknXcN3/rmhP8jgp69OfSe/JuKiQAFprJ7UGw7mwj7m4XcmDzlrnJDG+cGpphAINGdU3g3g7kDw==}
+    engines: {node: '>=22'}
 
   convert-source-map@2.0.0:
     resolution: {integrity: sha512-Kvp459HrV2FEJ1CAsi1Ku+MY3kasH19TFykTz2xWmMeq6bk2NU3XXvfJ+Q61m0xktWwt+1HSYf3JZsTms3aRJg==}
@@ -4685,13 +4685,13 @@ packages:
   matrix-events-sdk@0.0.1:
     resolution: {integrity: sha512-1QEOsXO+bhyCroIe2/A5OwaxHvBm7EsSQ46DEDn8RBIfQwN5HWBpFvyWWR4QY0KHPPnnJdI99wgRiAl7Ad5qaA==}
 
-  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/178dc6528ebc6a15e2f6fab38410127f16b500d0:
-    resolution: {gitHosted: true, integrity: sha512-UmlkoXs9VMZvNaDeQqBb2k+gLifnIqEZc5cxrLeEwdYEDakQLbRqrFtmvIp4ipUCjdIPkCgtzb7QLlpPBLAwqA==, tarball: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/178dc6528ebc6a15e2f6fab38410127f16b500d0}
-    version: 42.1.0
+  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/24929be0e741be6a5d0a7226f1c682e245263b8a:
+    resolution: {gitHosted: true, integrity: sha512-0EGwbXzvG88sBOxq4ZlCRwT4VpQj2xkizfyy0A3bTSK0ysb6/gXJ/o1WPFoqCjRGMDgPq4gAsk92xGtHA7EhPg==, tarball: https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/24929be0e741be6a5d0a7226f1c682e245263b8a}
+    version: 42.2.0
     engines: {node: '>=22.0.0'}
 
-  matrix-widget-api@1.18.0:
-    resolution: {integrity: sha512-4T2f2koWmx05p1BLcT/9YGGGPSXpPT+PA4Oap/5fjhXsWPxMGJiGL97YpANMYLKsnE1sScYFeuyxIgdc1Qo+Ew==}
+  matrix-widget-api@1.19.0:
+    resolution: {integrity: sha512-Qe7L6G1mQJphBC47/Bzp5ljPIK1UARgLiuGgS+/KmEs/eaNHkQ3+ArD0/0kvMV+d6kCGAZ9OKRqsnuPjizI+tw==}
 
   md5.js@1.3.5:
     resolution: {integrity: sha512-xitP+WxNPcTTOgnTJcrhM0xvdPepipPSf3I8EIpGKeFLjt3PlJLIDG3u8EX53ZIubkb+5U2+3rELYpEhHhzdkg==}
@@ -7102,7 +7102,7 @@ snapshots:
       '@types/dom-mediacapture-transform': 0.1.11
       livekit-client: 2.22.0(@types/dom-mediacapture-record@1.0.22)
 
-  '@matrix-org/matrix-sdk-crypto-wasm@18.4.0': {}
+  '@matrix-org/matrix-sdk-crypto-wasm@18.5.0': {}
 
   '@mdx-js/react@3.1.1(@types/react@19.2.17)(react@19.2.8)':
     dependencies:
@@ -8053,13 +8053,13 @@ snapshots:
   '@rolldown/binding-win32-x64-msvc@1.1.5':
     optional: true
 
-  '@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@7.29.7)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))':
+  '@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@8.0.0)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))':
     dependencies:
       '@babel/core': 7.29.7(supports-color@7.2.0)
       picomatch: 4.0.4
       rolldown: 1.1.5
     optionalDependencies:
-      '@babel/runtime': 7.29.7
+      '@babel/runtime': 8.0.0
       vite: 8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)
 
   '@rolldown/pluginutils@1.0.1': {}
@@ -8744,12 +8744,12 @@ snapshots:
       - '@types/react-dom'
       - react-dom
 
-  '@vitejs/plugin-react@6.0.5(@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@7.29.7)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)))(babel-plugin-react-compiler@1.0.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))':
+  '@vitejs/plugin-react@6.0.5(@rolldown/plugin-babel@0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@8.0.0)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)))(babel-plugin-react-compiler@1.0.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))':
     dependencies:
       '@rolldown/pluginutils': 1.0.1
       vite: 8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0)
     optionalDependencies:
-      '@rolldown/plugin-babel': 0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@7.29.7)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
+      '@rolldown/plugin-babel': 0.2.3(@babel/core@7.29.7(supports-color@7.2.0))(@babel/runtime@8.0.0)(rolldown@1.1.5)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))
       babel-plugin-react-compiler: 1.0.0
 
   '@vitest/browser-playwright@4.1.10(playwright@1.62.0)(vite@8.1.5(@types/node@24.13.3)(esbuild@0.28.1)(jiti@2.7.0)(sass@1.102.0)(terser@5.46.1)(yaml@2.9.0))(vitest@4.1.10)':
@@ -9195,7 +9195,7 @@ snapshots:
 
   constants-browserify@1.0.0: {}
 
-  content-type@2.0.0: {}
+  content-type@3.0.0: {}
 
   convert-source-map@2.0.0: {}
 
@@ -10275,21 +10275,21 @@ snapshots:
 
   matrix-events-sdk@0.0.1: {}
 
-  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/178dc6528ebc6a15e2f6fab38410127f16b500d0:
+  matrix-js-sdk@https://codeload.github.com/matrix-org/matrix-js-sdk/tar.gz/24929be0e741be6a5d0a7226f1c682e245263b8a:
     dependencies:
       '@babel/runtime': 8.0.0
-      '@matrix-org/matrix-sdk-crypto-wasm': 18.4.0
+      '@matrix-org/matrix-sdk-crypto-wasm': 18.5.0
       another-json: 0.2.0
       bs58: 6.0.0
-      content-type: 2.0.0
+      content-type: 3.0.0
       loglevel: 1.9.2
       matrix-events-sdk: 0.0.1
-      matrix-widget-api: 1.18.0
+      matrix-widget-api: 1.19.0
       p-retry: 8.0.0
       sdp-transform: 3.0.0
       unhomoglyph: 1.0.6
 
-  matrix-widget-api@1.18.0:
+  matrix-widget-api@1.19.0:
     dependencies:
       '@types/events': 3.0.3
       events: 3.3.0

src/config/ConfigOptions.ts

@@ -219,6 +219,18 @@ export interface ConfigOptions {
      * This is what goes into the m.rtc.member event expiry field and is typically set to a number of hours.
      */
     membership_event_expiry_ms?: number;
+
+    /**
+     * The number of participants in the session at which the media encryption key will no longer
+     * be rotated.
+     *
+     * Rotating a key requires sending it to every participant device, so in large sessions the
+     * cost of rotating on every join/leave becomes prohibitive. At this limit the current key is
+     * kept and distributed to new joiners; no new keys are generated for joiners/leavers.
+     *
+     * Defaults to the js-sdk default (undefined). Which means that rotation will always happen.
+     */
+    key_rotation_participant_limit?: number;
   };
 }
 
@@ -252,6 +264,7 @@ export interface ResolvedConfigOptions extends ConfigOptions {
     delayed_leave_event_restart_ms?: number;
     network_error_retry_ms: number;
     membership_event_expiry_ms?: number;
+    key_rotation_participant_limit?: number;
   };
 }
 

src/room/InCallView.test.tsx

@@ -22,7 +22,7 @@ import { TooltipProvider } from "@vector-im/compound-web";
 import { RoomContext, useLocalParticipant } from "@livekit/components-react";
 import userEvent from "@testing-library/user-event";
 
-import { InCallView } from "./InCallView";
+import { ActiveCall, InCallView } from "./InCallView";
 import {
   mockLivekitRoom,
   mockLocalParticipant,
@@ -33,7 +33,10 @@ import {
   type MockRTCSession,
 } from "../utils/test";
 import { E2eeType } from "../e2ee/e2eeType";
-import { getBasicCallViewModelEnvironment } from "../utils/test-viewmodel";
+import {
+  getBasicCallViewModelEnvironment,
+  getBasicRTCSession,
+} from "../utils/test-viewmodel";
 import {
   type CallViewModel,
   type CallViewModelOptions,
@@ -45,6 +48,8 @@ import { LivekitRoomAudioRenderer } from "../livekit/MatrixAudioRenderer";
 import { MediaDevicesContext } from "../MediaDevicesContext";
 import { type MediaDevices as ECMediaDevices } from "../state/MediaDevices";
 import { AppBar } from "../AppBar";
+import { type MatrixInfo } from "./VideoPreview";
+import { ProcessorProvider } from "../livekit/TrackProcessorContext";
 import { initializeWidget } from "../widget";
 
 initializeWidget();
@@ -78,6 +83,17 @@ const remoteParticipant = mockRemoteParticipant({
   identity: "@alice:example.org:AAAAAA",
 });
 
+const matrixInfo = {
+  userId: "",
+  displayName: "",
+  avatarUrl: "",
+  roomId: "",
+  roomName: "",
+  roomAlias: null,
+  roomAvatar: null,
+  e2eeSystem: { kind: E2eeType.NONE },
+} satisfies MatrixInfo;
+
 let useRoomEncryptionSystemMock: MockedFunction<typeof useRoomEncryptionSystem>;
 
 beforeEach(() => {
@@ -122,12 +138,13 @@ function createInCallView(args: CreateInCallViewArgs = {}): RenderResult & {
       remoteParticipants$: of([remoteParticipant]),
     },
   );
-  const { vm, footerVm, rtcSession } = getBasicCallViewModelEnvironment(
-    [local, alice],
-    undefined,
-    mediaDevices,
-    args.callViewModelOptions,
-  );
+  const { vm, footerVm, developerSettingsVm, rtcSession } =
+    getBasicCallViewModelEnvironment(
+      [local, alice],
+      undefined,
+      mediaDevices,
+      args.callViewModelOptions,
+    );
 
   rtcSession.joined = true;
   const room = rtcSession.room;
@@ -140,18 +157,8 @@ function createInCallView(args: CreateInCallViewArgs = {}): RenderResult & {
       muteStates={muteState}
       vm={vm}
       footerVm={footerVm}
-      matrixInfo={{
-        userId: "",
-        displayName: "",
-        avatarUrl: "",
-        roomId: "",
-        roomName: "",
-        roomAlias: null,
-        roomAvatar: null,
-        e2eeSystem: {
-          kind: E2eeType.NONE,
-        },
-      }}
+      developerSettingsVm={developerSettingsVm}
+      matrixInfo={matrixInfo}
       matrixRoom={room}
       onShareClick={null}
     />
@@ -226,3 +233,34 @@ describe("InCallView", () => {
     });
   });
 });
+
+describe("ActiveCall", () => {
+  it("creates the view models and renders the call", async () => {
+    const mediaDevices = mockMediaDevices({});
+    const { rtcSession, matrixRoom } = getBasicRTCSession([local, alice]);
+    const { findByTestId } = render(
+      <BrowserRouter>
+        <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>
+      </BrowserRouter>,
+    );
+    // Rendering at all proves ActiveCall created all of its view models
+    expect(await findByTestId("incall_leave")).toBeVisible();
+  });
+});

src/room/InCallView.tsx

@@ -83,6 +83,8 @@ import { ObservableScope } from "../state/ObservableScope.ts";
 import { CallFooter, type FooterSnapshot } from "../components/CallFooter.tsx";
 import { SettingsIconButton } from "../button/Button.tsx";
 import { createCallFooterViewModel } from "../components/CallFooterViewModel.tsx";
+import { createDeveloperSettingsTabViewModel } from "../settings/DeveloperSettingsTabViewModel.ts";
+import { type DeveloperSettingsSnapshot } from "../settings/DeveloperSettingsTab.tsx";
 import { type ViewModel } from "../state/ViewModel.ts";
 import { RingingStatus } from "../tile/RingingStatus.tsx";
 import { RingingAudioRenderer } from "./RingingAudioRenderer.tsx";
@@ -96,7 +98,7 @@ declare module "react" {
 
 export interface ActiveCallProps extends Omit<
   InCallViewProps,
-  "vm" | "livekitRoom" | "connState" | "footerVm"
+  "vm" | "livekitRoom" | "connState" | "footerVm" | "developerSettingsVm"
 > {
   e2eeSystem: EncryptionSystem;
   // TODO refactor those reasons into an enum
@@ -110,6 +112,9 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
   const [footerVm, setFooterVm] = useState<ViewModel<FooterSnapshot> | null>(
     null,
   );
+  const [developerSettingsVm, setDeveloperSettingsVm] =
+    useState<ViewModel<DeveloperSettingsSnapshot> | null>(null);
+
   const urlParams = useUrlParams();
   const mediaDevices = useMediaDevices();
   const trackProcessorState$ = useTrackProcessorObservable$();
@@ -169,6 +174,7 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
       `${props.client.getUserId()}:${props.client.getDeviceId()}`,
     );
     setFooterVm(footerVm);
+    setDeveloperSettingsVm(createDeveloperSettingsTabViewModel(scope, vm));
 
     return (): void => {
       scope.end();
@@ -188,10 +194,16 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
 
   if (vm === null) return null;
   if (footerVm === null) return null;
+  if (developerSettingsVm === null) return null;
 
   return (
     <ReactionsSenderProvider vm={vm} rtcSession={props.rtcSession}>
-      <InCallView {...props} vm={vm} footerVm={footerVm} />
+      <InCallView
+        {...props}
+        vm={vm}
+        footerVm={footerVm}
+        developerSettingsVm={developerSettingsVm}
+      />
     </ReactionsSenderProvider>
   );
 };
@@ -200,6 +212,7 @@ export interface InCallViewProps {
   client: MatrixClient;
   vm: CallViewModel;
   footerVm: ViewModel<FooterSnapshot>;
+  developerSettingsVm: ViewModel<DeveloperSettingsSnapshot>;
   matrixInfo: MatrixInfo;
   rtcSession: MatrixRTCSession;
   matrixRoom: MatrixRoom;
@@ -211,6 +224,7 @@ export const InCallView: FC<InCallViewProps> = ({
   client,
   vm,
   footerVm,
+  developerSettingsVm,
   matrixInfo,
   matrixRoom,
   muteStates,
@@ -256,6 +270,7 @@ export const InCallView: FC<InCallViewProps> = ({
   const audioParticipants = useBehavior(vm.livekitRoomItems$);
   const participantCount = useBehavior(vm.participantCount$);
   const reconnecting = useBehavior(vm.reconnecting$);
+  const screenShareError = useBehavior(vm.screenShareError$);
   const layout = useBehavior(vm.layout$);
   const edgeToEdge = useBehavior(vm.edgeToEdge$);
   const overflowing = useBehavior(vm.overflowing$);
@@ -385,6 +400,21 @@ export const InCallView: FC<InCallViewProps> = ({
       );
   }
 
+  const onDismissScreenShareToast = useCallback(
+    () => vm.dismissScreenShareError(),
+    [vm],
+  );
+  const screenShareToast = (
+    <Toast
+      onDismiss={onDismissScreenShareToast}
+      open={screenShareError !== null}
+      autoDismiss={5000}
+      modal={false}
+    >
+      {t("error.screen_share_failed")}
+    </Toast>
+  );
+
   // The reconnecting toast cannot be dismissed
   const onDismissReconnectingToast = useCallback(() => {}, []);
   // We need to use a non-modal toast to avoid trapping focus within the toast.
@@ -620,6 +650,7 @@ export const InCallView: FC<InCallViewProps> = ({
       <ReactionsAudioRenderer vm={vm} muted={muteAllAudio} />
       <RingingAudioRenderer vm={ringingVm} muted={muteAllAudio} />
       {reconnectingToast}
+      {screenShareToast}
       {earpieceOverlay}
       <ReactionsOverlay vm={vm} />
       {footer}
@@ -633,6 +664,7 @@ export const InCallView: FC<InCallViewProps> = ({
             onDismiss={(): void => setSettingsOpen(false)}
             tab={settingsTab}
             onTabChange={setSettingsTab}
+            developerSettingsVm={developerSettingsVm}
             livekitRooms={allConnections
               .getConnections()
               .map((connectionItem) => ({

src/room/__snapshots__/InCallView.test.tsx.snap

@@ -171,7 +171,7 @@ exports[`InCallView > rendering > renders 1`] = `
         class="_settingsLogoContainer_20b7b4"
       >
         <button
-          aria-labelledby="_r_8_"
+          aria-labelledby="_r_b_"
           class="_icon-button_1215g_8 _settingsOnlyShowWide_20b7b4"
           data-kind="secondary"
           data-testid="settings-bottom-left"
@@ -306,7 +306,7 @@ exports[`InCallView > rendering > renders 1`] = `
         class="_buttons_20b7b4"
       >
         <button
-          aria-labelledby="_r_d_"
+          aria-labelledby="_r_g_"
           class="_button_1nw83_8 _settingsOnlyShowNarrow_20b7b4 _has-icon_1nw83_60 _icon-only_1nw83_53"
           data-kind="secondary"
           data-size="lg"
@@ -331,7 +331,7 @@ exports[`InCallView > rendering > renders 1`] = `
           aria-busy="false"
           aria-checked="false"
           aria-disabled="true"
-          aria-labelledby="_r_i_"
+          aria-labelledby="_r_l_"
           class="_button_1nw83_8 _has-icon_1nw83_60 _icon-only_1nw83_53"
           data-kind="primary"
           data-size="lg"
@@ -356,7 +356,7 @@ exports[`InCallView > rendering > renders 1`] = `
           aria-busy="false"
           aria-checked="false"
           aria-disabled="true"
-          aria-labelledby="_r_n_"
+          aria-labelledby="_r_q_"
           class="_button_1nw83_8 _has-icon_1nw83_60 _icon-only_1nw83_53"
           data-kind="primary"
           data-size="lg"
@@ -381,7 +381,7 @@ exports[`InCallView > rendering > renders 1`] = `
           aria-disabled="false"
           aria-expanded="false"
           aria-haspopup="true"
-          aria-labelledby="_r_s_"
+          aria-labelledby="_r_v_"
           class="_button_1nw83_8 _raiseHand_20b7b4 _has-icon_1nw83_60 _icon-only_1nw83_53"
           data-kind="secondary"
           data-size="lg"
@@ -404,7 +404,7 @@ exports[`InCallView > rendering > renders 1`] = `
           </svg>
         </button>
         <button
-          aria-labelledby="_r_14_"
+          aria-labelledby="_r_17_"
           class="_button_1nw83_8 _has-icon_1nw83_60 _icon-only_1nw83_53 _destructive_1nw83_110"
           data-kind="primary"
           data-size="lg"
@@ -432,8 +432,8 @@ exports[`InCallView > rendering > renders 1`] = `
         data-size="lg"
       >
         <input
-          aria-labelledby="_r_1a_"
-          name="_r_19_"
+          aria-labelledby="_r_1d_"
+          name="_r_1c_"
           type="radio"
           value="spotlight"
         />
@@ -452,9 +452,9 @@ exports[`InCallView > rendering > renders 1`] = `
           />
         </svg>
         <input
-          aria-labelledby="_r_1f_"
+          aria-labelledby="_r_1i_"
           checked=""
-          name="_r_19_"
+          name="_r_1c_"
           type="radio"
           value="grid"
         />

src/settings/DeveloperSettingsTab.test.tsx

@@ -12,7 +12,12 @@ import { TooltipProvider } from "@vector-im/compound-web";
 
 import type { MatrixClient } from "matrix-js-sdk";
 import type { Room as LivekitRoom } from "livekit-client";
-import { DeveloperSettingsTab } from "./DeveloperSettingsTab";
+import {
+  DeveloperSettingsTab,
+  type DeveloperSettingsSnapshot,
+} from "./DeveloperSettingsTab";
+import { outOfCallDeveloperSettingsTabViewModel } from "./DeveloperSettingsTabViewModel";
+import { createStaticViewModel } from "../state/ViewModel";
 import { getSFUConfigWithOpenID } from "../livekit/openIDSFU";
 import {
   customLivekitUrl as customLivekitUrlSetting,
@@ -107,6 +112,7 @@ describe("DeveloperSettingsTab", () => {
         roomId={"#room:example.org"}
         livekitRooms={livekitRooms}
         env={{ MY_MOCK_ENV: 10, ENV: "test" } as unknown as ImportMetaEnv}
+        vm={outOfCallDeveloperSettingsTabViewModel}
       />,
     );
 
@@ -136,6 +142,7 @@ describe("DeveloperSettingsTab", () => {
           <DeveloperSettingsTab
             client={client}
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -159,6 +166,7 @@ describe("DeveloperSettingsTab", () => {
             client={client}
             roomId="#testRoom"
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -181,6 +189,7 @@ describe("DeveloperSettingsTab", () => {
             client={client}
             roomId="#testRoom"
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -206,6 +215,7 @@ describe("DeveloperSettingsTab", () => {
             client={client}
             roomId="#testRoom"
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -236,6 +246,7 @@ describe("DeveloperSettingsTab", () => {
             client={client}
             roomId="#testRoom"
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -273,6 +284,7 @@ describe("DeveloperSettingsTab", () => {
           <DeveloperSettingsTab
             client={client}
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -305,6 +317,7 @@ describe("DeveloperSettingsTab", () => {
           <DeveloperSettingsTab
             client={client}
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -345,6 +358,7 @@ describe("DeveloperSettingsTab", () => {
           <DeveloperSettingsTab
             client={client}
             env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
           />
         </TooltipProvider>,
       );
@@ -378,6 +392,7 @@ describe("DeveloperSettingsTab", () => {
             <DeveloperSettingsTab
               client={client}
               env={{} as unknown as ImportMetaEnv}
+              vm={outOfCallDeveloperSettingsTabViewModel}
             />
           </TooltipProvider>,
         );
@@ -400,4 +415,74 @@ describe("DeveloperSettingsTab", () => {
       },
     );
   });
+
+  describe("KeyRotationStatus", () => {
+    it("displays active status when key rotation is not suppressed", async () => {
+      const client = createMockMatrixClient();
+      const vm = createStaticViewModel<DeveloperSettingsSnapshot>({
+        keyRotation: { suppressed: false, participantCount: 5 },
+      });
+
+      render(
+        <TooltipProvider>
+          <DeveloperSettingsTab
+            client={client}
+            env={{} as unknown as ImportMetaEnv}
+            vm={vm}
+          />
+        </TooltipProvider>,
+      );
+
+      await waitFor(() =>
+        expect(
+          screen.getByText(/Media key rotation: active \(5 participants\)/),
+        ).toBeInTheDocument(),
+      );
+    });
+
+    it("displays suppressed status when key rotation is suppressed", async () => {
+      const client = createMockMatrixClient();
+      const vm = createStaticViewModel<DeveloperSettingsSnapshot>({
+        keyRotation: { suppressed: true, participantCount: 50 },
+      });
+
+      render(
+        <TooltipProvider>
+          <DeveloperSettingsTab
+            client={client}
+            env={{} as unknown as ImportMetaEnv}
+            vm={vm}
+          />
+        </TooltipProvider>,
+      );
+
+      await waitFor(() =>
+        expect(
+          screen.getByText(
+            /Media key rotation: suppressed, participant limit reached \(50 participants\)/,
+          ),
+        ).toBeInTheDocument(),
+      );
+    });
+
+    it("does not render KeyRotationStatus when not in a call", async () => {
+      const client = createMockMatrixClient();
+
+      render(
+        <TooltipProvider>
+          <DeveloperSettingsTab
+            client={client}
+            env={{} as unknown as ImportMetaEnv}
+            vm={outOfCallDeveloperSettingsTabViewModel}
+          />
+        </TooltipProvider>,
+      );
+
+      await waitFor(() =>
+        expect(
+          screen.queryByText(/Media key rotation:/),
+        ).not.toBeInTheDocument(),
+      );
+    });
+  });
 });

src/settings/DeveloperSettingsTab.tsx

@@ -68,6 +68,39 @@ import settingsStyles from "./SettingsModal.module.css";
 import { Slider } from "../Slider";
 import { useUrlParams } from "../UrlParams";
 import { getSFUConfigWithOpenID } from "../livekit/openIDSFU";
+import { useBehavior } from "../useBehavior";
+import { type ViewModel } from "../state/ViewModel.ts";
+
+/**
+ * The state of MatrixRTC's media key rotation.
+ */
+export interface KeyRotationInfo {
+  /** Whether the call is large enough that MatrixRTC has stopped rotating the media key. */
+  suppressed: boolean;
+  participantCount: number;
+}
+
+/**
+ * The Snapshot combines all fields the developer settings tab needs from the
+ * surrounding call. Everything else in this tab is read from the settings store
+ * or the environment directly.
+ */
+export interface DeveloperSettingsSnapshot {
+  /** The media key rotation state, or `null` when we are not in a call. */
+  keyRotation: KeyRotationInfo | null;
+}
+
+/**
+ * Shows whether the call is large enough that MatrixRTC has stopped rotating the media key.
+ */
+const KeyRotationStatus: FC<{ info: KeyRotationInfo }> = ({ info }) => (
+  <p>
+    Media key rotation:{" "}
+    {info.suppressed
+      ? `suppressed, participant limit reached (${info.participantCount} participants)`
+      : `active (${info.participantCount} participants)`}
+  </p>
+);
 
 interface Props {
   client: MatrixClient;
@@ -79,6 +112,7 @@ interface Props {
     livekitAlias?: string;
   }[];
   env: ImportMetaEnv;
+  vm: ViewModel<DeveloperSettingsSnapshot>;
 }
 
 export const DeveloperSettingsTab: FC<Props> = ({
@@ -86,8 +120,10 @@ export const DeveloperSettingsTab: FC<Props> = ({
   livekitRooms,
   roomId,
   env,
+  vm,
 }) => {
   const { t } = useTranslation();
+  const keyRotation = useBehavior(vm.keyRotation$);
   const [duplicateTiles, setDuplicateTiles] = useSetting(duplicateTilesSetting);
   const [debugTileLayout, setDebugTileLayout] = useSetting(
     debugTileLayoutSetting,
@@ -364,6 +400,7 @@ export const DeveloperSettingsTab: FC<Props> = ({
           id: client.getDeviceId() || "unknown",
         })}
       </p>
+      {keyRotation !== null && <KeyRotationStatus info={keyRotation} />}
       <Separator />
       <FieldRow>
         <InputField

src/settings/DeveloperSettingsTabViewModel.test.ts

@@ -0,0 +1,48 @@
+/*
+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 { BehaviorSubject } from "rxjs";
+
+import { testScope } from "../utils/test";
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel";
+import {
+  createDeveloperSettingsTabViewModel,
+  outOfCallDeveloperSettingsTabViewModel,
+} from "./DeveloperSettingsTabViewModel";
+
+describe("createDeveloperSettingsTabViewModel", () => {
+  it("projects the key rotation state of the call", () => {
+    const keyRotationSuppressed$ = new BehaviorSubject(false);
+    const participantCount$ = new BehaviorSubject(5);
+    const vm = createDeveloperSettingsTabViewModel(testScope(), {
+      keyRotationSuppressed$,
+      participantCount$,
+    } as unknown as CallViewModel);
+
+    expect(vm.keyRotation$.value).toEqual({
+      suppressed: false,
+      participantCount: 5,
+    });
+
+    participantCount$.next(50);
+    keyRotationSuppressed$.next(true);
+
+    expect(vm.keyRotation$.value).toEqual({
+      suppressed: true,
+      participantCount: 50,
+    });
+  });
+});
+
+describe("outOfCallDeveloperSettingsTabViewModel", () => {
+  it("has no key rotation state", () => {
+    expect(outOfCallDeveloperSettingsTabViewModel.keyRotation$.value).toBe(
+      null,
+    );
+  });
+});

src/settings/DeveloperSettingsTabViewModel.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 { combineLatest } from "rxjs";
+
+import { type CallViewModel } from "../state/CallViewModel/CallViewModel.ts";
+import { type ObservableScope } from "../state/ObservableScope.ts";
+import { createStaticViewModel, type ViewModel } from "../state/ViewModel.ts";
+import { type DeveloperSettingsSnapshot } from "./DeveloperSettingsTab.tsx";
+
+/**
+ * Creates the ViewModel for the developer settings tab while in a call.
+ *
+ * Only the call state the tab actually renders is projected here, so that the
+ * tab does not need to know about the CallViewModel.
+ *
+ * @param scope - ObservableScope that bounds the lifetime of derived behaviors.
+ * @param callModel - The root CallViewModel; provides the key rotation state.
+ */
+export function createDeveloperSettingsTabViewModel(
+  scope: ObservableScope,
+  callModel: CallViewModel,
+): ViewModel<DeveloperSettingsSnapshot> {
+  return {
+    keyRotation$: scope.behavior(
+      combineLatest(
+        [callModel.keyRotationSuppressed$, callModel.participantCount$],
+        (suppressed, participantCount) => ({ suppressed, participantCount }),
+      ),
+    ),
+  };
+}
+
+/**
+ * The ViewModel for the developer settings tab outside of a call (lobby, user
+ * menu), where no call state exists. All call specific fields are `null`.
+ */
+export const outOfCallDeveloperSettingsTabViewModel: ViewModel<DeveloperSettingsSnapshot> =
+  createStaticViewModel<DeveloperSettingsSnapshot>({ keyRotation: null });

src/settings/SettingsModal.tsx

@@ -29,11 +29,16 @@ import { PreferencesSettingsTab } from "./PreferencesSettingsTab";
 import { Slider } from "../Slider";
 import { DeviceSelection } from "./DeviceSelection";
 import { useTrackProcessor } from "../livekit/TrackProcessorContext";
-import { DeveloperSettingsTab } from "./DeveloperSettingsTab";
+import {
+  DeveloperSettingsTab,
+  type DeveloperSettingsSnapshot,
+} from "./DeveloperSettingsTab";
 import { FieldRow, InputField } from "../input/Input";
 import { useSubmitRageshake } from "./submit-rageshake";
 import { useUrlParams } from "../UrlParams";
 import { useBehavior } from "../useBehavior";
+import { type ViewModel } from "../state/ViewModel.ts";
+import { outOfCallDeveloperSettingsTabViewModel } from "./DeveloperSettingsTabViewModel";
 
 type SettingsTab =
   | "audio"
@@ -56,6 +61,8 @@ interface Props {
     url: string;
     isLocal?: boolean;
   }[];
+  /** Only available while in a call. Used by the developer tab. */
+  developerSettingsVm?: ViewModel<DeveloperSettingsSnapshot>;
 }
 
 export const defaultSettingsTab: SettingsTab = "audio";
@@ -68,6 +75,7 @@ export const SettingsModal: FC<Props> = ({
   client,
   roomId,
   livekitRooms,
+  developerSettingsVm,
 }) => {
   const { t } = useTranslation();
 
@@ -220,6 +228,7 @@ export const SettingsModal: FC<Props> = ({
         client={client}
         livekitRooms={livekitRooms}
         roomId={roomId}
+        vm={developerSettingsVm ?? outOfCallDeveloperSettingsTabViewModel}
       />
     ),
   };

src/settings/rageshake.flush.test.ts

@@ -0,0 +1,52 @@
+/*
+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, expect, it, vi } from "vitest";
+
+import { init as initRageshake } from "./rageshake";
+
+afterEach(() => {
+  vi.useRealTimers();
+  vi.unstubAllGlobals();
+});
+
+it("flushes logs to IndexedDB periodically without an explicit flush", async () => {
+  vi.useFakeTimers();
+  const add = vi.fn();
+  const txn = {
+    oncomplete: undefined as (() => void) | undefined,
+    onerror: undefined,
+    objectStore: (name: string) =>
+      name === "logs"
+        ? {
+            add: (entry: unknown): void => {
+              add(entry);
+              queueMicrotask(() => txn.oncomplete?.());
+            },
+          }
+        : { put: vi.fn() },
+  };
+  const open = (): unknown => {
+    const req = {
+      result: { transaction: () => txn },
+      onsuccess: undefined as (() => void) | undefined,
+    };
+    queueMicrotask(() => req.onsuccess?.());
+    return req;
+  };
+  vi.stubGlobal("indexedDB", { open });
+
+  await initRageshake();
+  global.mx_rage_logger.log(1, "test", "hello from the buffer");
+  expect(add).not.toHaveBeenCalled();
+
+  await vi.advanceTimersByTimeAsync(2000);
+  expect(add).toHaveBeenCalledOnce();
+  expect(add.mock.calls[0][0]).toMatchObject({
+    lines: expect.stringContaining("hello from the buffer"),
+  });
+});

src/settings/rageshake.ts

@@ -204,10 +204,13 @@ class IndexedDBLogStore {
   // Throttled function to flush logs. We use throttle rather
   // than debounce as we want logs to be written regularly, otherwise
   // if there's a constant stream of logging, we'd never write anything.
-  private throttledFlush = throttle(() => this.flush, MAX_FLUSH_INTERVAL_MS, {
-    leading: false,
-    trailing: true,
-  });
+  private throttledFlush = throttle(
+    () => {
+      this.flush().catch((e) => logger.error("Failed to flush logs", e));
+    },
+    MAX_FLUSH_INTERVAL_MS,
+    { leading: false, trailing: true },
+  );
 
   /**
    * Flush logs to disk.

src/state/CallViewModel/CallViewModel.ts

@@ -114,6 +114,7 @@ import {
   type LocalTransport,
 } from "./localMember/LocalTransport.ts";
 import {
+  createKeyRotationSuppressed$,
   createMemberships$,
   membershipsAndTransports$,
 } from "../SessionBehaviors.ts";
@@ -266,6 +267,11 @@ export interface CallViewModel {
    * Whether we are sharing our screen.
    */
   sharingScreen$: Behavior<boolean>;
+  /**
+   * The last error from toggling screen sharing, until dismissed.
+   */
+  screenShareError$: Behavior<Error | null>;
+  dismissScreenShareError: () => void;
 
   // UI interactions
   /**
@@ -302,6 +308,12 @@ export interface CallViewModel {
    *    multiple devices.
    */
   participantCount$: Behavior<number>;
+  /**
+   * Whether the call has grown large enough that MatrixRTC has stopped rotating the media
+   * encryption key. While this is true the key in use is still shared with new joiners, but no new
+   * key is generated when someone joins or leaves.
+   */
+  keyRotationSuppressed$: Behavior<boolean>;
   allConnections$: Behavior<ConnectionManagerData>;
   /** Participants sorted by livekit room so they can be used in the audio rendering */
   livekitRoomItems$: Behavior<LivekitRoomItem[]>;
@@ -861,6 +873,11 @@ export function createCallViewModel$(
     matrixLivekitMembers$.pipe(map((ms) => ms.length)),
   );
 
+  const keyRotationSuppressed$ = createKeyRotationSuppressed$(
+    scope,
+    matrixRTCSession,
+  );
+
   const leaveSoundEffect$ = userMedia$.pipe(
     pairwise(),
     filter(
@@ -1797,6 +1814,7 @@ export function createCallViewModel$(
     ),
     allConnections$,
     participantCount$: participantCount$,
+    keyRotationSuppressed$: keyRotationSuppressed$,
     handsRaised$: handsRaised$,
     reactions$: reactions$,
     joinSoundEffect$: joinSoundEffect$,
@@ -1845,6 +1863,8 @@ export function createCallViewModel$(
     reconnecting$: localMembership.reconnecting$,
     livekitRoomItems$,
     connected$: localMembership.connected$,
+    screenShareError$: localMembership.screenShareError$,
+    dismissScreenShareError: localMembership.dismissScreenShareError,
   };
 }
 

src/state/CallViewModel/localMember/LocalMember.test.ts

@@ -31,6 +31,7 @@ import {
   flushPromises,
   mockConfig,
   mockLivekitRoom,
+  mockLocalParticipant,
   mockMuteStates,
   withTestScheduler,
   ownMemberMock,
@@ -41,6 +42,7 @@ import {
   enterRTCSession,
   PublishState,
   TrackState,
+  watchScreenShareToggle,
 } from "./LocalMember";
 import {
   FailToGetOpenIdToken,
@@ -68,6 +70,31 @@ vi.mock("@livekit/components-core", () => ({
     .mockReturnValue(of({ isScreenShareEnabled: false })),
 }));
 
+describe("watchScreenShareToggle", () => {
+  it("reports nothing when the toggle completes", async () => {
+    const onError = vi.fn();
+    watchScreenShareToggle(Promise.resolve(), true, logger, onError);
+    await flushPromises();
+    expect(onError).not.toHaveBeenCalled();
+  });
+
+  it("reports failures other than the user cancelling", async () => {
+    const onError = vi.fn();
+    const e = new Error("NotReadableError");
+    watchScreenShareToggle(Promise.reject(e), true, logger, onError);
+    await flushPromises();
+    expect(onError).toHaveBeenCalledWith(e);
+  });
+
+  it("does not report the user cancelling the picker", async () => {
+    const onError = vi.fn();
+    const cancelled = new DOMException("Permission denied", "NotAllowedError");
+    watchScreenShareToggle(Promise.reject(cancelled), true, logger, onError);
+    await flushPromises();
+    expect(onError).not.toHaveBeenCalled();
+  });
+});
+
 describe("LocalMembership", () => {
   describe("enterRTCSession", () => {
     it("It joins the correct Session", () => {
@@ -121,6 +148,57 @@ describe("LocalMembership", () => {
         expect.objectContaining({ manageMediaKeys: true }),
       );
     });
+
+    it("passes keyRotationParticipantLimit from config to joinRTCSession", () => {
+      mockConfig({
+        livekit: { livekit_service_url: "http://my-default-service-url.com" },
+        matrix_rtc_session: {
+          delayed_leave_event_delay_ms: 0,
+          network_error_retry_ms: 0,
+          key_rotation_participant_limit: 50,
+        },
+      });
+
+      const mockedSession = vi.mocked({
+        room: {
+          roomId: "roomId",
+          client: {
+            getDomain: vi.fn().mockReturnValue("example.org"),
+            getOpenIdToken: vi.fn().mockResolvedValue({
+              access_token: "ACCCESS_TOKEN",
+              token_type: "Bearer",
+              matrix_server_name: "localhost",
+              expires_in: 10000,
+            }),
+          },
+        },
+        memberships: [],
+        joinRTCSession: vi.fn(),
+      }) as unknown as MatrixRTCSession;
+
+      enterRTCSession(
+        mockedSession,
+        ownMemberMock,
+        {
+          livekit_alias: "roomId",
+          livekit_service_url: "http://my-livekit-service-url.com",
+          type: "livekit",
+        },
+        {
+          encryptMedia: true,
+          matrixRTCMode: MATRIX_RTC_MODE,
+        },
+      );
+
+      expect(mockedSession.joinRTCSession).toHaveBeenLastCalledWith(
+        expect.any(Object),
+        [],
+        expect.any(Object),
+        expect.objectContaining({
+          keyRotationParticipantLimit: 50,
+        }),
+      );
+    });
   });
 
   const defaultCreateLocalMemberValues = {
@@ -803,4 +881,98 @@ describe("LocalMembership", () => {
       scope.end();
     });
   });
+
+  describe("toggleScreenSharing", () => {
+    let originalMediaDevices: MediaDevices | undefined;
+
+    beforeAll(() => {
+      mockConfig();
+      // Screen sharing is only offered when getDisplayMedia is available.
+      originalMediaDevices = navigator.mediaDevices;
+      Object.defineProperty(navigator, "mediaDevices", {
+        configurable: true,
+        value: { getDisplayMedia: vi.fn() },
+      });
+    });
+
+    afterAll(() => {
+      Object.defineProperty(navigator, "mediaDevices", {
+        configurable: true,
+        value: originalMediaDevices,
+      });
+    });
+
+    const createMembershipWithConnection = (
+      connection: Connection | null,
+    ): {
+      scope: ObservableScope;
+      localMembership: ReturnType<typeof createLocalMembership$>;
+    } => {
+      const scope = new ObservableScope();
+      const connectionManagerData = new ConnectionManagerData();
+      if (connection) connectionManagerData.add(connection, []);
+      const localMembership = createLocalMembership$({
+        scope,
+        ...defaultCreateLocalMemberValues,
+        connectionManager: {
+          connectionManagerData$: constant(new Epoch(connectionManagerData)),
+        },
+        localTransport$: new BehaviorSubject({
+          advertised$: new BehaviorSubject(aTransport),
+          active$: new BehaviorSubject(aTransportWithSFUConfig),
+        }),
+      });
+      return { scope, localMembership };
+    };
+
+    it("surfaces a failure and clears it on dismiss", async () => {
+      const error = new Error("NotReadableError");
+      const setScreenShareEnabled = vi.fn().mockRejectedValue(error);
+      const connection = {
+        state$: constant(ConnectionState.LivekitConnected),
+        transport: aTransport,
+        livekitRoom: mockLivekitRoom({
+          localParticipant: mockLocalParticipant({
+            isScreenShareEnabled: false,
+            setScreenShareEnabled,
+          }),
+        }),
+      } as unknown as Connection;
+      const { scope, localMembership } =
+        createMembershipWithConnection(connection);
+      await flushPromises();
+
+      expect(localMembership.toggleScreenSharing).not.toBeNull();
+      expect(localMembership.screenShareError$.value).toBeNull();
+
+      localMembership.toggleScreenSharing!();
+      await flushPromises();
+
+      expect(setScreenShareEnabled).toHaveBeenCalledWith(
+        true,
+        expect.any(Object),
+        undefined,
+      );
+      expect(localMembership.screenShareError$.value).toBe(error);
+
+      localMembership.dismissScreenShareError();
+      expect(localMembership.screenShareError$.value).toBeNull();
+
+      scope.end();
+    });
+
+    it("does nothing when there is no local participant", async () => {
+      // No connection means participant$ never resolves to a participant.
+      const { scope, localMembership } = createMembershipWithConnection(null);
+      await flushPromises();
+
+      expect(localMembership.toggleScreenSharing).not.toBeNull();
+      localMembership.toggleScreenSharing!();
+      await flushPromises();
+
+      expect(localMembership.screenShareError$.value).toBeNull();
+
+      scope.end();
+    });
+  });
 });

src/state/CallViewModel/localMember/LocalMember.ts

@@ -196,6 +196,11 @@ export const createLocalMembership$ = ({
    * Callback to toggle screen sharing. If null, screen sharing is not possible.
    */
   toggleScreenSharing: (() => void) | null;
+  /**
+   * The last error from toggling screen sharing, until dismissed.
+   */
+  screenShareError$: Behavior<Error | null>;
+  dismissScreenShareError: () => void;
   // tracks$: Behavior<LocalTrack[]>;
   participant$: Behavior<LocalParticipant | null>;
   connection$: Behavior<Connection | null>;
@@ -706,6 +711,7 @@ export const createLocalMembership$ = ({
     ),
   );
 
+  const screenShareError$ = new BehaviorSubject<Error | null>(null);
   let toggleScreenSharing: (() => void) | null = null;
   if (
     "getDisplayMedia" in (navigator.mediaDevices ?? {}) &&
@@ -777,13 +783,18 @@ export const createLocalMembership$ = ({
       // We also allow screen sharing to be toggled even if the connection
       // is still initializing or publishing tracks, because there's no
       // technical reason to disallow this. LiveKit will publish if it can.
-      participant$.value
-        ?.setScreenShareEnabled(
+      const participant = participant$.value;
+      if (!participant) return;
+      watchScreenShareToggle(
+        participant.setScreenShareEnabled(
           targetScreenshareState,
           screenshareSettings,
           publishOptions,
-        )
-        .catch(logger.error);
+        ),
+        targetScreenshareState,
+        logger,
+        (e) => screenShareError$.next(e),
+      );
     };
   }
 
@@ -802,11 +813,44 @@ export const createLocalMembership$ = ({
     ),
     sharingScreen$,
     toggleScreenSharing,
+    screenShareError$,
+    dismissScreenShareError: () => screenShareError$.next(null),
     connection$: localConnection$,
     internalLoggerRef: logger,
   };
 };
 
+/**
+ * Logs the outcome of a screen share toggle and reports failures.
+ *
+ * getDisplayMedia may legitimately take a long time (the user is choosing
+ * what to share) or never settle at all, so nothing is inferred from silence:
+ * the request and its completion are logged with the elapsed time so that a
+ * hang is visible in the logs, and only an explicit rejection is reported.
+ *
+ * The user cancelling the picker rejects with a NotAllowedError; that is
+ * logged but not reported.
+ */
+export function watchScreenShareToggle(
+  toggle: Promise<unknown>,
+  enable: boolean,
+  logger: Logger,
+  onError: (e: Error) => void,
+): void {
+  const what = `Screen share ${enable ? "start" : "stop"}`;
+  const started = Date.now();
+  const elapsed = (): string => `${Date.now() - started} ms`;
+  logger.info(`${what} requested`);
+  toggle.then(
+    () => logger.info(`${what} completed in ${elapsed()}`),
+    (e: unknown) => {
+      logger.error(`${what} failed after ${elapsed()}:`, e);
+      if (e instanceof DOMException && e.name === "NotAllowedError") return;
+      onError(e instanceof Error ? e : new Error(String(e)));
+    },
+  );
+}
+
 export function observeSharingScreen$(p: Participant): Observable<boolean> {
   return observeParticipantEvents(
     p,
@@ -902,6 +946,8 @@ export function enterRTCSession(
       makeKeyDelay: matrixRtcSessionConfig?.wait_for_key_rotation_ms,
       membershipEventExpiryMs:
         matrixRtcSessionConfig?.membership_event_expiry_ms,
+      keyRotationParticipantLimit:
+        matrixRtcSessionConfig?.key_rotation_participant_limit,
       unstableSendStickyEvents: matrixRTCMode === MatrixRTCMode.Matrix_2_0,
       maximumNetworkErrorRetryCount: maximumNetworkErrorRetryCount,
     },

src/state/SessionBehaviors.test.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2025 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 { MatrixRTCSessionEvent } from "matrix-js-sdk/lib/matrixrtc";
+import { EventEmitter } from "events";
+
+import { createKeyRotationSuppressed$ } from "./SessionBehaviors";
+import { testScope } from "../utils/test";
+
+describe("SessionBehaviors", () => {
+  describe("createKeyRotationSuppressed$", () => {
+    it("emits initial value from isKeyRotationSuppressed and updates when KeyRotationSuppressedChanged event is emitted", () => {
+      const scope = testScope();
+      const emitter = new EventEmitter();
+      const mockSession = Object.assign(emitter, {
+        on: vi.fn(),
+        off: vi.fn(),
+        isKeyRotationSuppressed: false,
+      });
+
+      const keyRotationSuppressed$ = createKeyRotationSuppressed$(
+        scope,
+        mockSession as any,
+      );
+
+      expect(keyRotationSuppressed$.value).toBe(false);
+      emitter.emit(MatrixRTCSessionEvent.KeyRotationSuppressedChanged, true);
+
+      expect(keyRotationSuppressed$.value).toBe(true);
+
+      emitter.emit(MatrixRTCSessionEvent.KeyRotationSuppressedChanged, false);
+
+      expect(keyRotationSuppressed$.value).toBe(false);
+    });
+  });
+});

src/state/SessionBehaviors.ts

@@ -88,3 +88,22 @@ export const createMemberships$ = (
     new Epoch(matrixRTCSession.memberships),
   );
 };
+
+/**
+ * Whether the session has grown large enough that MatrixRTC has stopped rotating the media
+ * encryption key. While this is true the key in use is still shared with new joiners, but no new
+ * key is generated when someone joins or leaves.
+ */
+export const createKeyRotationSuppressed$ = (
+  scope: ObservableScope,
+  matrixRTCSession: MatrixRTCSession,
+): Behavior<boolean> => {
+  return scope.behavior(
+    fromEvent(
+      matrixRTCSession,
+      MatrixRTCSessionEvent.KeyRotationSuppressedChanged,
+      (suppressed: boolean) => suppressed,
+    ),
+    matrixRTCSession.isKeyRotationSuppressed,
+  );
+};

src/utils/test-viewmodel.ts

@@ -42,6 +42,8 @@ import { MatrixRTCMode } from "../config/ConfigOptions";
 import { createCallFooterViewModel } from "../components/CallFooterViewModel";
 import { type FooterSnapshot } from "../components/CallFooter";
 import { type ViewModel } from "../state/ViewModel";
+import { createDeveloperSettingsTabViewModel } from "../settings/DeveloperSettingsTabViewModel";
+import { type DeveloperSettingsSnapshot } from "../settings/DeveloperSettingsTab";
 
 mockConfig({ livekit: { livekit_service_url: "https://example.com" } });
 
@@ -140,6 +142,7 @@ export function getBasicCallViewModelEnvironment(
 ): {
   vm: CallViewModel;
   footerVm: ViewModel<FooterSnapshot>;
+  developerSettingsVm: ViewModel<DeveloperSettingsSnapshot>;
   rtcMemberships$: BehaviorSubject<CallMembership[]>;
   rtcSession: MockRTCSession;
   handRaisedSubject$: BehaviorSubject<Record<string, RaisedHandInfo>>;
@@ -188,6 +191,7 @@ export function getBasicCallViewModelEnvironment(
   return {
     vm,
     footerVm,
+    developerSettingsVm: createDeveloperSettingsTabViewModel(testScope(), vm),
     rtcMemberships$,
     rtcSession,
     handRaisedSubject$: handRaisedSubject$,

src/utils/test.ts

@@ -487,6 +487,8 @@ export class MockRTCSession extends TypedEventEmitter<
     return this.joined;
   }
 
+  public isKeyRotationSuppressed = false;
+
   public withMemberships(
     rtcMembers$: Behavior<Partial<CallMembership>[]>,
   ): MockRTCSession {