🐛(frontend) stop reporting screen-share denials as errors

Add a small helper that classifies a `getDisplayMedia` failure as a
user, browser, or OS permission denial, or returns null when it is
a genuine error.

Chromium reports denials with explicit, non-localized messages:

* "Permission denied by user" when the user cancels or dismisses
  the source picker.
* "Permission denied by system" when the OS blocks capture (e.g.
  the macOS Screen Recording privacy setting).
* Plain "Permission denied" for browser-level blocks (site
  settings, enterprise policy, permissions-policy).

Firefox and Safari use generic `NotAllowedError` messages, which
fall into the "browser" bucket.

Firefox additionally does not map macOS Screen Recording (TCC)
blocks to `NotAllowedError`: the OS silently returns no capturable
sources, so `getDisplayMedia` rejects with `NotFoundError` ("The
object can not be found here."). Same quirk as the mic/cam OS blocks
handled in `useWatchMediaDeviceErrors` via `isLikelySystemNotFound`.

Behavior on a denied screen-share permission:

* Denials are expected outcomes (picker cancelled by the user, OS
  privacy settings, enterprise policy…) and no longer surface as
  exceptions in error tracking; capture an analytics event instead.
* Only OS-level blocks get the modal, since it explains how to
  unblock them.

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to
 - 🐛(frontend) implement hysteresis band for the control bar layout
 - 🐛(frontend) fix toolbar ResizeObserver loop and alignment drift
 - 🐛(analytics) filter benign ResizeObserver loop error in Sentry/PostHog
+- 🐛(frontend) stop reporting screen-share denials as errors
 
 ## [1.26.0] - 2026-08-12
 

src/frontend/src/features/analytics/telemetry.ts

@@ -137,6 +137,7 @@ export const captureMediaEvent = async (
     | 'media-device-success'
     | 'device-not-found'
     | 'permissions-denied'
+    | 'screen-share-permission-denied'
     | 'silent-mic-detected'
     | 'silent-mic-analyser-unavailable'
     | 'silent-mic-recovered'

src/frontend/src/features/rooms/livekit/prefabs/VideoConference.tsx

@@ -11,7 +11,9 @@ import { SidePanel } from '../components/SidePanel'
 import { RecordingProvider } from '@/features/recording'
 import { ScreenShareErrorModal } from '../components/ScreenShareErrorModal'
 import { ConnectionObserver } from '../components/ConnectionObserver'
-import { reportError } from '@/features/analytics/telemetry'
+import { captureMediaEvent, reportError } from '@/features/analytics/telemetry'
+import { getOS } from '@/utils/os'
+import { isFireFox } from '@/utils/livekit'
 import { MediaStateObserver } from '../components/MediaStateObserver'
 import { RoomMetadataSynchronizer } from '../components/RoomMetadataSynchronizer'
 import { useNoiseReduction } from '../hooks/useNoiseReduction'
@@ -36,6 +38,20 @@ export interface VideoConferenceProps extends React.HTMLAttributes<HTMLDivElemen
   SettingsComponent?: React.ComponentType
 }
 
+const getScreenSharePermissionDeniedScope = (
+  error: Error
+): 'system' | 'user' | 'browser' | null => {
+  if (error.name === 'NotAllowedError') {
+    if (/by system/i.test(error.message)) return 'system'
+    if (/by user/i.test(error.message)) return 'user'
+    return 'browser'
+  }
+  if (error.name === 'NotFoundError' && isFireFox() && getOS() === 'macos') {
+    return 'system'
+  }
+  return null
+}
+
 /**
  * The `VideoConference` ready-made component is your drop-in solution for a classic video conferencing application.
  * It provides functionality such as focusing on one participant, grid view with pagination to handle large numbers
@@ -61,6 +77,34 @@ export function VideoConference({ ...props }: VideoConferenceProps) {
 
   const [isShareErrorVisible, setIsShareErrorVisible] = useState(false)
 
+  const handleDeviceError = ({
+    source,
+    error,
+  }: {
+    source: Track.Source
+    error: Error
+  }) => {
+    if (source === Track.Source.ScreenShare) {
+      const scope = getScreenSharePermissionDeniedScope(error)
+      if (scope) {
+        if (scope === 'system') setIsShareErrorVisible(true)
+        void captureMediaEvent('screen-share-permission-denied', {
+          at: 'ControlBar.onDeviceError',
+          source,
+          error_name: error.name,
+          error_message: error.message,
+          denied_scope: scope,
+          os: getOS(),
+        })
+        return
+      }
+    }
+    reportError('device_switch_failure', error, {
+      at: 'ControlBar.onDeviceError',
+      source,
+    })
+  }
+
   return (
     <>
       <RoomMetadataSynchronizer />
@@ -92,21 +136,7 @@ export function VideoConference({ ...props }: VideoConferenceProps) {
                 <StageLayout />
               )}
             </RoomContentArea>
-            <ControlBar
-              onDeviceError={(e) => {
-                reportError('device_switch_failure', e.error, {
-                  at: 'ControlBar.onDeviceError',
-                  source: e.source,
-                })
-                if (
-                  e.source == Track.Source.ScreenShare &&
-                  e.error.toString() ==
-                    'NotAllowedError: Permission denied by system'
-                ) {
-                  setIsShareErrorVisible(true)
-                }
-              }}
-            />
+            <ControlBar onDeviceError={handleDeviceError} />
             <SidePanel />
           </>
         )}