perf(P6C.T12): optimistic UI for mute / mentions-only / archive / pin / device-revoke

Audit of write-actions revealed that send (and edit via realtime UPDATE) are
already optimistic via local state insertion in `useConversationMessages`,
and friend nicknames are pure-local localStorage. Five user-write actions
were waiting on the ~100-200 ms server roundtrip + realtime echo:

* Toggle mute (`setConversationMutedUntil`)
* Toggle mentions-only (`setConversationMentionsOnly`)
* Toggle archive (`setConversationArchived`)
* Pin / unpin message (`pinMessage` / `unpinMessage`)
* Revoke device (`revokeDevice` RPC)

All five now flip local state synchronously and roll back on failure. The
existing realtime subscriptions reconcile canonically (no-op when the
optimistic patch already matches the server row), so this is purely a UX
latency improvement — no protocol or persistence changes.

Reactions (`toggleReaction` / `voteExclusive`) were intentionally skipped
this round: rollback semantics for the exclusive-vote path with multiple
sequential awaits are messy enough to warrant a dedicated pass.

apps/desktop/src/lib/usePinnedMessages.ts

@@ -1,12 +1,26 @@
 import { listPinnedMessages, type PinnedMessage } from '@chat-app/shared/chat';
-import { useEffect, useState } from 'react';
+import { useCallback, useEffect, useState } from 'react';
 
 import { supabase } from './supabase';
 
+export interface UsePinnedMessagesResult {
+  pins: PinnedMessage[];
+  // Optimistic insert. Caller flips the UI immediately; server insert +
+  // realtime echo will reconcile (dedup'd by messageId). Returns the
+  // previous snapshot so the caller can roll back on error.
+  applyOptimisticPin: (messageId: string, pinnedBy: string) => PinnedMessage[];
+  applyOptimisticUnpin: (messageId: string) => PinnedMessage[];
+  // Hard restore for rollback after a failed server call.
+  restorePins: (snapshot: PinnedMessage[]) => void;
+}
+
 // Live list of pinned messages for one conversation. Subscribes to the
 // `pinned_messages` realtime channel for the conv so the header pill +
-// side-panel update without a refetch.
-export function usePinnedMessages(conversationId: string | undefined): PinnedMessage[] {
+// side-panel update without a refetch. The `applyOptimistic*` helpers let
+// callers flip local state synchronously on user action so the pin button
+// doesn't appear unresponsive while the ~100-200ms server roundtrip + the
+// realtime refetch round complete.
+export function usePinnedMessages(conversationId: string | undefined): UsePinnedMessagesResult {
   const [pins, setPins] = useState<PinnedMessage[]>([]);
 
   useEffect(() => {
@@ -44,5 +58,42 @@ export function usePinnedMessages(conversationId: string | undefined): PinnedMes
     };
   }, [conversationId]);
 
-  return pins;
+  const applyOptimisticPin = useCallback<UsePinnedMessagesResult['applyOptimisticPin']>(
+    (messageId, pinnedBy) => {
+      if (!conversationId) return pins;
+      let snapshot: PinnedMessage[] = pins;
+      setPins((prev) => {
+        snapshot = prev;
+        if (prev.some((p) => p.messageId === messageId)) return prev;
+        const optimistic: PinnedMessage = {
+          conversationId,
+          messageId,
+          pinnedBy,
+          pinnedAt: new Date().toISOString(),
+        };
+        // Newest first matches the listPinnedMessages order.
+        return [optimistic, ...prev];
+      });
+      return snapshot;
+    },
+    [conversationId, pins],
+  );
+
+  const applyOptimisticUnpin = useCallback<UsePinnedMessagesResult['applyOptimisticUnpin']>(
+    (messageId) => {
+      let snapshot: PinnedMessage[] = pins;
+      setPins((prev) => {
+        snapshot = prev;
+        return prev.filter((p) => p.messageId !== messageId);
+      });
+      return snapshot;
+    },
+    [pins],
+  );
+
+  const restorePins = useCallback<UsePinnedMessagesResult['restorePins']>((snapshot) => {
+    setPins(snapshot);
+  }, []);
+
+  return { pins, applyOptimisticPin, applyOptimisticUnpin, restorePins };
 }