fix(correctness): call-join reset on embed swap + per-path notify dedupe

COR-2 (useCallEmbed): useCallJoined only reset `joined` when the embed became
undefined. Answering a 2nd call swaps the embed A->B directly (embed stays
truthy), so `joined` stayed true and call B rendered as already-joined,
skipping the loading/watchdog UI. Re-seed from `embed?.joined ?? false` on
every embed identity change.

COR-4 (ClientNonUIFeatures): the notify-dedupe used one Map<roomId,eventId>
slot shared by the main-timeline and per-thread paths, so a thread reply
overwrote the room's slot and a re-fired main message (decrypt/edit re-emit,
common in E2EE) then mismatched and double-notified. Key the slot by
`${roomId}|${threadId ?? 'main'}` so each path dedupes independently.

Both verified correct by two review passes (no missed-notification or
missed-join regressions).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/hooks/useCallEmbed.ts

@@ -149,9 +149,11 @@ export const useCallJoined = (embed?: CallEmbed): boolean => {
   );
 
   useEffect(() => {
-    if (!embed) {
-      setJoined(false);
-    }
+    // Re-seed from the (new) embed whenever it changes identity, not only when
+    // it becomes undefined. Answering a 2nd call swaps embed A→B directly (embed
+    // stays truthy), so a plain `if (!embed)` reset left `joined` stuck true and
+    // B rendered as already-joined, skipping the loading/watchdog UI.
+    setJoined(embed?.joined ?? false);
   }, [embed]);
 
   return joined;

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -373,8 +373,10 @@ function StatusExpiryMonitor() {
 
 function MessageNotifications() {
   const audioRef = useRef<HTMLAudioElement>(null);
+  // Notify dedupe, keyed `${roomId}|${threadId ?? 'main'}` -> last notified
+  // eventId, so the main timeline and each thread dedupe independently.
   const lastNotifiedEventRef = useRef<Map<string, string>>(new Map());
-  // Per-thread dedupe: threadId -> last notified eventId.
+  // Per-thread dedupe (thread-detection gate): threadId -> last notified eventId.
   const lastNotifiedThreadRef = useRef<Map<string, string>>(new Map());
   const mx = useMatrixClient();
   const useAuthentication = useMediaAuthentication();
@@ -513,12 +515,16 @@ function MessageNotifications() {
       const eventId = mEvent.getId();
       if (!sender || !eventId) return;
 
-      // Dedupe on the event id (per room): the same event can re-fire (decryption,
-      // edit, thread repopulation). This replaces the old unread-COUNT dedupe,
-      // which suppressed a genuinely-new message whenever its post-read count
-      // matched the previously-notified count — i.e. "read a DM, next message
-      // never notifies/sounds" (the common one-at-a-time cadence).
-      if (lastNotifiedEventRef.current.get(room.roomId) === eventId) return;
+      // Dedupe on the event id (per room AND per path): the same event can
+      // re-fire (decryption, edit, thread repopulation). The main timeline and
+      // each thread get their own slot — a shared per-room slot let a thread
+      // reply overwrite the main slot, so a re-fired main message then mismatched
+      // and double-notified. This replaces the old unread-COUNT dedupe, which
+      // suppressed a genuinely-new message whenever its post-read count matched
+      // the previously-notified count (the "read a DM, next message never
+      // notifies/sounds" one-at-a-time cadence).
+      const dedupeKey = `${room.roomId}|${threadId ?? 'main'}`;
+      if (lastNotifiedEventRef.current.get(dedupeKey) === eventId) return;
 
       // Main-timeline path respects push rules: don't notify when the room has no
       // notification count (e.g. a non-mention in a Mentions-only room). The
@@ -527,7 +533,7 @@ function MessageNotifications() {
       // override in a Mentions-only room is silently dropped.
       if (!threadId && getUnreadInfo(room).total === 0) return;
 
-      lastNotifiedEventRef.current.set(room.roomId, eventId);
+      lastNotifiedEventRef.current.set(dedupeKey, eventId);
 
       const quietActive =
         focusAssistActive ||