From bf5482db8c742a7c6729b167e70b2a5a5d2ca81b Mon Sep 17 00:00:00 2001
From: Matthew Hodgson <matthew@matrix.org>
Date: Thu, 3 Sep 2026 14:55:31 +0100
Subject: [PATCH 1/3] Surface screen share failures instead of silently doing
 nothing

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.
---
 locales/en/app.json                           |  1 +
 src/room/InCallView.tsx                       | 17 ++++++
 .../__snapshots__/InCallView.test.tsx.snap    | 20 +++----
 src/state/CallViewModel/CallViewModel.ts      |  7 +++
 .../localMember/LocalMember.test.ts           | 26 ++++++++++
 .../CallViewModel/localMember/LocalMember.ts  | 52 +++++++++++++++++--
 6 files changed, 109 insertions(+), 14 deletions(-)

diff --git a/locales/en/app.json b/locales/en/app.json
index 543942e2e..f3d568bb8 100644
--- a/locales/en/app.json
+++ b/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."
diff --git a/src/room/InCallView.tsx b/src/room/InCallView.tsx
index a57dcce2b..3ea88f81f 100644
--- a/src/room/InCallView.tsx
+++ b/src/room/InCallView.tsx
@@ -270,6 +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$);
@@ -399,6 +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.
@@ -634,6 +650,7 @@ export const InCallView: FC<InCallViewProps> = ({
       <ReactionsAudioRenderer vm={vm} muted={muteAllAudio} />
       <RingingAudioRenderer vm={ringingVm} muted={muteAllAudio} />
       {reconnectingToast}
+      {screenShareToast}
       {earpieceOverlay}
       <ReactionsOverlay vm={vm} />
       {footer}
diff --git a/src/room/__snapshots__/InCallView.test.tsx.snap b/src/room/__snapshots__/InCallView.test.tsx.snap
index 984e2b12e..7cd044bfc 100644
--- a/src/room/__snapshots__/InCallView.test.tsx.snap
+++ b/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"
         />
diff --git a/src/state/CallViewModel/CallViewModel.ts b/src/state/CallViewModel/CallViewModel.ts
index 09f73d1a6..c854363be 100644
--- a/src/state/CallViewModel/CallViewModel.ts
+++ b/src/state/CallViewModel/CallViewModel.ts
@@ -267,6 +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
   /**
@@ -1858,6 +1863,8 @@ export function createCallViewModel$(
     reconnecting$: localMembership.reconnecting$,
     livekitRoomItems$,
     connected$: localMembership.connected$,
+    screenShareError$: localMembership.screenShareError$,
+    dismissScreenShareError: localMembership.dismissScreenShareError,
   };
 }
 
diff --git a/src/state/CallViewModel/localMember/LocalMember.test.ts b/src/state/CallViewModel/localMember/LocalMember.test.ts
index 9ea6bb72c..09d863aa2 100644
--- a/src/state/CallViewModel/localMember/LocalMember.test.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.test.ts
@@ -41,6 +41,7 @@ import {
   enterRTCSession,
   PublishState,
   TrackState,
+  watchScreenShareToggle,
 } from "./LocalMember";
 import {
   FailToGetOpenIdToken,
@@ -68,6 +69,31 @@ 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", () => {
diff --git a/src/state/CallViewModel/localMember/LocalMember.ts b/src/state/CallViewModel/localMember/LocalMember.ts
index 2f4fde26b..dfe8936a7 100644
--- a/src/state/CallViewModel/localMember/LocalMember.ts
+++ b/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,

From b22eba7af92a03fc1bd8bd59999fca7da9b7934e Mon Sep 17 00:00:00 2001
From: Johannes Marbach <n0-0ne+github@mailbox.org>
Date: Fri, 4 Sep 2026 07:39:58 +0200
Subject: [PATCH 2/3] Add further tests

---
 .../localMember/LocalMember.test.ts           | 96 +++++++++++++++++++
 1 file changed, 96 insertions(+)

diff --git a/src/state/CallViewModel/localMember/LocalMember.test.ts b/src/state/CallViewModel/localMember/LocalMember.test.ts
index 09d863aa2..b270db13e 100644
--- a/src/state/CallViewModel/localMember/LocalMember.test.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.test.ts
@@ -31,6 +31,7 @@ import {
   flushPromises,
   mockConfig,
   mockLivekitRoom,
+  mockLocalParticipant,
   mockMuteStates,
   withTestScheduler,
   ownMemberMock,
@@ -880,4 +881,99 @@ 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();
+    });
+  });
 });

From bae8da3ddc0b6e367bbbae622b741b03b3b0c543 Mon Sep 17 00:00:00 2001
From: Johannes Marbach <n0-0ne+github@mailbox.org>
Date: Fri, 4 Sep 2026 07:44:16 +0200
Subject: [PATCH 3/3] Reformat

---
 src/state/CallViewModel/localMember/LocalMember.test.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/state/CallViewModel/localMember/LocalMember.test.ts b/src/state/CallViewModel/localMember/LocalMember.test.ts
index b270db13e..aec641776 100644
--- a/src/state/CallViewModel/localMember/LocalMember.test.ts
+++ b/src/state/CallViewModel/localMember/LocalMember.test.ts
@@ -963,8 +963,7 @@ describe("LocalMembership", () => {
 
     it("does nothing when there is no local participant", async () => {
       // No connection means participant$ never resolves to a participant.
-      const { scope, localMembership } =
-        createMembershipWithConnection(null);
+      const { scope, localMembership } = createMembershipWithConnection(null);
       await flushPromises();
 
       expect(localMembership.toggleScreenSharing).not.toBeNull();