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

@@ -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."

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}

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_"
+          aria-labelledby="_r_1d_"
-          name="_r_19_"
+          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/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,
   };
 }
 

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", () => {

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$.value
+      const participant = participant$.value;
-        ?.setScreenShareEnabled(
+      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,