fix(web): Address review findings for M4-LLM integration

- Sanitize user-facing error messages (no raw API/DB errors)
- Remove dead try/catch from Chat.tsx handleSendMessage
- Add onError callback for persistence errors in useChat
- Add console.error logging to loadConversation
- Guard minimize/toggleMinimize against closed overlay state
- Improve error dedup bucketing for non-DOMException errors
- Add tests: non-Error throws, updateConversation failure,
  minimize/toggleMinimize guards

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

apps/web/src/components/chat/Chat.test.tsx

@@ -176,22 +176,19 @@ describe("Chat", () => {
     });
   });
 
-  describe("sendMessage error handling", () => {
-    it("should log error when sendMessage fails", async () => {
-      const sendError = new Error("Send failed");
-      const mockSendMessage = vi.fn().mockRejectedValue(sendError);
+  describe("sendMessage delegation", () => {
+    it("should delegate to useChat.sendMessage without extra error handling", async () => {
+      const mockSendMessage = vi.fn().mockResolvedValue(undefined);
       mockUseChat.mockReturnValue(createMockUseChatReturn({ sendMessage: mockSendMessage }));
 
       const ref = createRef<ChatRef>();
       const { getByTestId } = render(<Chat ref={ref} />);
 
-      // Click the send button (which calls handleSendMessage)
       const sendButton = getByTestId("chat-input");
       sendButton.click();
 
-      // Wait for async handling
       await vi.waitFor(() => {
-        expect(consoleSpy).toHaveBeenCalledWith("Error sending message:", sendError);
+        expect(mockSendMessage).toHaveBeenCalledWith("test message");
       });
     });
   });

apps/web/src/components/chat/Chat.tsx

@@ -73,9 +73,6 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
   } = useChat({
     model: "llama3.2",
     ...(initialProjectId !== undefined && { projectId: initialProjectId }),
-    onError: (_err) => {
-      // Error is handled by the useChat hook's state
-    },
   });
 
   // Connect to WebSocket for real-time updates (when we have a user)
@@ -180,11 +177,7 @@ export const Chat = forwardRef<ChatRef, ChatProps>(function Chat(
 
   const handleSendMessage = useCallback(
     async (content: string) => {
-      try {
-        await sendMessage(content);
-      } catch (err) {
-        console.error("Error sending message:", err);
-      }
+      await sendMessage(content);
     },
     [sendMessage]
   );