fix(calls): the call bar shows "Call disconnected" and reconnects when sync is back (#318)

After a homeserver stall Element Call showed "Connection lost" while the
call bar still looked joined. Handle the fork's io.lotus.call_error:
show "Call disconnected" with a Reconnect button (io.lotus.reconnect),
and reconnect automatically once sync is back.

Fixes #318

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/hooks/useCallError.ts

@@ -0,0 +1,41 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import { SyncState } from 'matrix-js-sdk';
+import { CALL_ERROR_CHANGED, CallControl } from '../plugins/call/CallControl';
+import { CallErrorState } from '../plugins/call/callError';
+import { useMatrixClient } from './useMatrixClient';
+import { useSyncState } from './useSyncState';
+
+/** [Gitea #318] The fork's current call error (null while the call is fine). */
+export function useCallError(control: CallControl): CallErrorState {
+  const [err, setErr] = useState(control.callError);
+  useEffect(() => {
+    const on = () => setErr(control.callError);
+    on();
+    control.on(CALL_ERROR_CHANGED, on);
+    return () => {
+      control.off(CALL_ERROR_CHANGED, on);
+    };
+  }, [control]);
+  return err;
+}
+
+/**
+ * [Gitea #318] After a homeserver stall the call drops with "Connection
+ * lost". Once sync is back, reconnect automatically (once per drop).
+ */
+export function useReconnectWhenSynced(control: CallControl): void {
+  const mx = useMatrixClient();
+  const err = useCallError(control);
+  const tried = useRef<CallErrorState>(null);
+  useSyncState(
+    mx,
+    useCallback(
+      (state: SyncState | null) => {
+        if (state !== SyncState.Syncing || !err?.recoverable || tried.current === err) return;
+        tried.current = err;
+        control.reconnect();
+      },
+      [err, control],
+    ),
+  );
+}