feat(chat-switch): hydrate useConversationMessages from in-memory cache

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/desktop/src/lib/useConversationMessages.ts

@@ -33,6 +33,11 @@ import {
   shouldGiveUp,
   subscribeOutbox,
 } from './messageOutbox';
+import {
+  getCachedMessages,
+  hasCachedMessages,
+  setCachedMessages,
+} from './messageMemoryCache';
 import { supabase } from './supabase';
 import { cachedUserKey } from './userIdentity';
 
@@ -82,7 +87,20 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
   retryPending: (id: string) => void;
   cancelPending: (id: string) => void;
 } {
-  const [state, setState] = useState<State>({ messages: [], loading: true, error: null });
+  // Initialize from the in-memory cache so a previously-viewed chat shows
+  // content on the very first render after the parent remounts on `:id`
+  // change. `loading` stays true ONLY for never-seen conversations (cache
+  // miss) so the spinner doesn't flash on every chat switch.
+  const [state, setState] = useState<State>(() => {
+    if (conversationId && hasCachedMessages(conversationId)) {
+      return {
+        messages: getCachedMessages(conversationId),
+        loading: false,
+        error: null,
+      };
+    }
+    return { messages: [], loading: true, error: null };
+  });
   const [pending, setPending] = useState<OutboxItem[]>(() =>
     conversationId ? getOutbox(conversationId) : [],
   );
@@ -229,6 +247,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
       const rows = await fetchConversationMessages(supabase, conversationId);
       const decrypted = await decryptBatch(rows);
       setState({ messages: decrypted, loading: false, error: null });
+      setCachedMessages(conversationId, decrypted);
       // Persist the fresh batch to the local cache so next conversation
       // switch / app start can hydrate instantly. Fire-and-forget — cache
       // write failure is never user-visible.
@@ -248,12 +267,17 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
   // when the server response lands. On cache-miss this is a ~5ms no-op.
   useEffect(() => {
     if (!conversationId) return;
+    // Memory cache already populated state synchronously — skip the disk
+    // round-trip entirely. The canonical data lands shortly via refresh();
+    // the SQLite cache only matters for cold-start hydration.
+    if (hasCachedMessages(conversationId)) return;
     let cancelled = false;
     void loadCachedMessages(conversationId).then((cached) => {
       if (cancelled || cached.length === 0) return;
       setState((prev) => {
         // Don't clobber a fresh server response that already landed.
         if (prev.messages.length > 0) return prev;
+        setCachedMessages(conversationId, cached);
         return { messages: cached, loading: false, error: null };
       });
     });
@@ -338,7 +362,9 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
       if (!decrypted) return;
       setState((prev) => {
         if (prev.messages.some((m) => m.id === decrypted!.id)) return prev;
-        return { ...prev, messages: [...prev.messages, decrypted!] };
+        const next = [...prev.messages, decrypted!];
+        if (conversationId) setCachedMessages(conversationId, next);
+        return { ...prev, messages: next };
       });
     },
     [conversationId, deviceId, decryptBatch],
@@ -358,6 +384,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
           editedAt: partial.editedAt,
           deletedAt: partial.deletedAt,
         };
+        if (conversationId) setCachedMessages(conversationId, next);
         return { ...prev, messages: next };
       });
       if (partial.editedAt && !partial.deletedAt) {
@@ -421,6 +448,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
           if (idx === -1) return prev;
           const next = [...prev.messages];
           next[idx] = decrypted!;
+          if (conversationId) setCachedMessages(conversationId, next);
           return { ...prev, messages: next };
         });
       }
@@ -428,14 +456,18 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
     [conversationId, deviceId, decryptBatch],
   );
 
-  const handleDelete = useCallback((row: Record<string, unknown>) => {
-    const id = String(row.id);
-    setState((prev) => ({
-      ...prev,
-      messages: prev.messages.filter((m) => m.id !== id),
-    }));
-    void deleteCachedMessage(id);
-  }, []);
+  const handleDelete = useCallback(
+    (row: Record<string, unknown>) => {
+      const id = String(row.id);
+      setState((prev) => {
+        const next = prev.messages.filter((m) => m.id !== id);
+        if (conversationId) setCachedMessages(conversationId, next);
+        return { ...prev, messages: next };
+      });
+      void deleteCachedMessage(id);
+    },
+    [conversationId],
+  );
 
   useEffect(() => {
     if (!conversationId || !userId || !deviceId) return;
@@ -552,13 +584,12 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
       });
       setState((prev) => {
         if (prev.messages.some((m) => m.id === msg.id)) return prev;
-        return {
-          ...prev,
-          messages: [
-            ...prev.messages,
-            { ...msg, plaintext: text } as DecryptedMessage,
-          ],
-        };
+        const next = [
+          ...prev.messages,
+          { ...msg, plaintext: text } as DecryptedMessage,
+        ];
+        setCachedMessages(convId, next);
+        return { ...prev, messages: next };
       });
     },
     [],
@@ -686,16 +717,15 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
           : JSON.stringify({ v: 1, text: trimmed, attachments: handles });
       setState((prev) => {
         if (prev.messages.some((m) => m.id === msg.id)) return prev;
-        return {
-          ...prev,
-          messages: [
-            ...prev.messages,
-            {
-              ...msg,
-              plaintext: attachmentsPayload,
-            } as DecryptedMessage,
-          ],
-        };
+        const next = [
+          ...prev.messages,
+          {
+            ...msg,
+            plaintext: attachmentsPayload,
+          } as DecryptedMessage,
+        ];
+        setCachedMessages(conversationId, next);
+        return { ...prev, messages: next };
       });
 
       // 4. Insert public attachment metadata rows pointing at the new message.