feat(calls): toast when a room admin turns off screen sharing / camera mid-call (#223)

Re-measured the revoke on the current stack (guard fix + fork lotus.4): the
SFU drops the sharer's tracks and EC's own button, the captured tracks and our
control bar all follow within ~2-4 s — the 30 s lag is gone. What remained was
that the button simply vanished with no explanation, so a call-lifetime hook
now toasts 'Screen sharing was turned off by a room admin.' (or the camera
variant) when a track ends while the room policy forbids it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/CallEmbedProvider.tsx

@@ -46,6 +46,7 @@ import { useMatrixClient } from '../hooks/useMatrixClient';
 import { previewRingtone, startRingtone, unlockRingtoneAudio } from '../utils/ringtones';
 import { useCallMembersChange, useCallSession } from '../hooks/useCall';
 import { useCallJoinLeaveSounds } from '../hooks/useCallJoinLeaveSounds';
+import { useCallPolicyRevokedToast } from '../hooks/useCallPolicyRevokedToast';
 import { useCallHotkeys } from '../hooks/useCallHotkeys';
 import { useAfkAutoMute } from '../hooks/useAfkAutoMute';
 import { useCallQuality } from '../hooks/useCallQuality';
@@ -685,6 +686,7 @@ function CallUtils({ embed, joined }: { embed: CallEmbed; joined: boolean }) {
   useCallHotkeys(embed, joined);
   useAfkAutoMute(joined ? embed : undefined);
   useCallJoinLeaveSounds(embed);
+  useCallPolicyRevokedToast(embed, joined);
   useCallThemeSync(embed);
   useCallQuality(embed);
   useCallHangupEvent(

src/app/hooks/useCallPolicyRevokedToast.ts

@@ -0,0 +1,39 @@
+import { useEffect, useRef } from 'react';
+import { useSetAtom } from 'jotai';
+import { CallEmbed, useCallControlState } from '../plugins/call';
+import { useRoomCallPolicy } from './useRoomCallPolicy';
+import { toastQueueAtom } from '../state/toast';
+
+/**
+ * [Gitea #223] When a room admin turns Allow Screen Sharing / Allow Camera
+ * off mid-call, the voice-limit-guard revokes the publish permission and the
+ * SFU drops our track within seconds — the button just vanishes with no
+ * explanation. Tell the user why: a track that went away while the room policy
+ * forbids it was not their doing.
+ */
+export function useCallPolicyRevokedToast(embed: CallEmbed, joined: boolean): void {
+  const { screenshare, video } = useCallControlState(embed.control);
+  const { allowScreenshare, allowCamera } = useRoomCallPolicy(embed.room);
+  const setToast = useSetAtom(toastQueueAtom);
+  const prev = useRef({ screenshare, video });
+
+  useEffect(() => {
+    const was = prev.current;
+    prev.current = { screenshare, video };
+    if (!joined) return;
+    const notify = (body: string) =>
+      setToast({
+        id: `call-policy-${Date.now()}`,
+        displayName: 'Lotus Chat',
+        body,
+        roomName: embed.room.name ?? 'Voice call',
+        roomId: embed.roomId,
+      });
+    if (was.screenshare && !screenshare && !allowScreenshare) {
+      notify('Screen sharing was turned off by a room admin.');
+    }
+    if (was.video && !video && !allowCamera) {
+      notify('Your camera was turned off by a room admin.');
+    }
+  }, [screenshare, video, allowScreenshare, allowCamera, joined, setToast, embed]);
+}