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/hooks/useChat.test.ts

@@ -33,6 +33,9 @@ const mockSendChatMessage = chatApi.sendChatMessage as MockedFunction<
 const mockCreateConversation = ideasApi.createConversation as MockedFunction<
   typeof ideasApi.createConversation
 >;
+const mockUpdateConversation = ideasApi.updateConversation as MockedFunction<
+  typeof ideasApi.updateConversation
+>;
 const mockGetIdea = ideasApi.getIdea as MockedFunction<typeof ideasApi.getIdea>;
 
 /**
@@ -156,6 +159,7 @@ describe("useChat", () => {
     });
 
     it("should handle API errors gracefully", async () => {
+      vi.spyOn(console, "error").mockImplementation(() => undefined);
       mockSendChatMessage.mockRejectedValueOnce(new Error("API Error"));
 
       const onError = vi.fn();
@@ -165,11 +169,11 @@ describe("useChat", () => {
         await result.current.sendMessage("Hello");
       });
 
-      expect(result.current.error).toBe("API Error");
+      expect(result.current.error).toBe("Unable to send message. Please try again.");
       expect(onError).toHaveBeenCalledWith(expect.any(Error));
       // Should have welcome + user + error message
       expect(result.current.messages).toHaveLength(3);
-      expect(result.current.messages[2]?.content).toContain("Error: API Error");
+      expect(result.current.messages[2]?.content).toBe("Something went wrong. Please try again.");
     });
   });
 
@@ -403,6 +407,7 @@ describe("useChat", () => {
 
   describe("clearError", () => {
     it("should clear error state", async () => {
+      vi.spyOn(console, "error").mockImplementation(() => undefined);
       mockSendChatMessage.mockRejectedValueOnce(new Error("Test error"));
 
       const { result } = renderHook(() => useChat());
@@ -411,7 +416,7 @@ describe("useChat", () => {
         await result.current.sendMessage("Hello");
       });
 
-      expect(result.current.error).toBe("Test error");
+      expect(result.current.error).toBe("Unable to send message. Please try again.");
 
       act(() => {
         result.current.clearError();
@@ -505,10 +510,10 @@ describe("useChat", () => {
         await result.current.sendMessage("Hello");
       });
 
-      expect(result.current.error).toBe("Model not available");
+      expect(result.current.error).toBe("Unable to send message. Please try again.");
       // Should have welcome + user + error message
       expect(result.current.messages).toHaveLength(3);
-      expect(result.current.messages[2]?.content).toContain("Error: Model not available");
+      expect(result.current.messages[2]?.content).toBe("Something went wrong. Please try again.");
     });
 
     it("should keep assistant message visible when save fails", async () => {
@@ -586,9 +591,71 @@ describe("useChat", () => {
       const saveError = result2.current.error;
 
       // They should be different
-      expect(llmError).toBe("Timeout");
+      expect(llmError).toBe("Unable to send message. Please try again.");
       expect(saveError).toContain("Message sent but failed to save");
       expect(llmError).not.toEqual(saveError);
     });
+
+    it("should handle non-Error throws from LLM API", async () => {
+      vi.spyOn(console, "error").mockImplementation(() => undefined);
+      mockSendChatMessage.mockRejectedValueOnce("string error");
+
+      const onError = vi.fn();
+      const { result } = renderHook(() => useChat({ onError }));
+
+      await act(async () => {
+        await result.current.sendMessage("Hello");
+      });
+
+      expect(result.current.error).toBe("Unable to send message. Please try again.");
+      expect(onError).toHaveBeenCalledWith(expect.any(Error));
+      expect(result.current.messages[2]?.content).toBe("Something went wrong. Please try again.");
+    });
+
+    it("should handle non-Error throws from persistence layer", async () => {
+      vi.spyOn(console, "error").mockImplementation(() => undefined);
+      mockSendChatMessage.mockResolvedValueOnce(createMockChatResponse("OK"));
+      mockCreateConversation.mockRejectedValueOnce("DB string error");
+
+      const onError = vi.fn();
+      const { result } = renderHook(() => useChat({ onError }));
+
+      await act(async () => {
+        await result.current.sendMessage("Hello");
+      });
+
+      // Assistant message should still be visible
+      expect(result.current.messages[2]?.content).toBe("OK");
+      expect(result.current.error).toBe("Message sent but failed to save. Please try again.");
+      expect(onError).toHaveBeenCalledWith(expect.any(Error));
+    });
+
+    it("should handle updateConversation failure for existing conversations", async () => {
+      vi.spyOn(console, "error").mockImplementation(() => undefined);
+
+      // First message succeeds and creates conversation
+      mockSendChatMessage.mockResolvedValueOnce(createMockChatResponse("First response"));
+      mockCreateConversation.mockResolvedValueOnce(createMockIdea("conv-1", "Test", ""));
+
+      const { result } = renderHook(() => useChat());
+
+      await act(async () => {
+        await result.current.sendMessage("First");
+      });
+
+      expect(result.current.conversationId).toBe("conv-1");
+
+      // Second message succeeds but updateConversation fails
+      mockSendChatMessage.mockResolvedValueOnce(createMockChatResponse("Second response"));
+      mockUpdateConversation.mockRejectedValueOnce(new Error("Connection reset"));
+
+      await act(async () => {
+        await result.current.sendMessage("Second");
+      });
+
+      // Assistant message should still be visible
+      expect(result.current.messages[4]?.content).toBe("Second response");
+      expect(result.current.error).toBe("Message sent but failed to save. Please try again.");
+    });
   });
 });

apps/web/src/hooks/useChat.ts

@@ -214,16 +214,18 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
         } catch (saveErr) {
           const saveErrorMsg =
             saveErr instanceof Error ? saveErr.message : "Unknown persistence error";
-          setError(`Message sent but failed to save: ${saveErrorMsg}`);
+          setError("Message sent but failed to save. Please try again.");
+          onError?.(saveErr instanceof Error ? saveErr : new Error(saveErrorMsg));
           console.error("Failed to save conversation", {
             error: saveErr,
             errorType: "PERSISTENCE_ERROR",
             conversationId,
+            detail: saveErrorMsg,
           });
         }
       } catch (err) {
         const errorMsg = err instanceof Error ? err.message : "Failed to send message";
-        setError(errorMsg);
+        setError("Unable to send message. Please try again.");
         onError?.(err instanceof Error ? err : new Error(errorMsg));
         console.error("Failed to send chat message", {
           error: err,
@@ -240,7 +242,7 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
         const errorMessage: Message = {
           id: `error-${String(Date.now())}`,
           role: "assistant",
-          content: `Error: ${errorMsg}`,
+          content: "Something went wrong. Please try again.",
           createdAt: new Date().toISOString(),
         };
         setMessages((prev) => [...prev, errorMessage]);
@@ -280,8 +282,15 @@ export function useChat(options: UseChatOptions = {}): UseChatReturn {
         setConversationTitle(idea.title ?? null);
       } catch (err) {
         const errorMsg = err instanceof Error ? err.message : "Failed to load conversation";
-        setError(errorMsg);
+        setError("Unable to load conversation. Please try again.");
         onError?.(err instanceof Error ? err : new Error(errorMsg));
+        console.error("Failed to load conversation", {
+          error: err,
+          errorType: "LOAD_ERROR",
+          ideaId,
+          timestamp: new Date().toISOString(),
+        });
+        throw err;
       } finally {
         setIsLoading(false);
       }

apps/web/src/hooks/useChatOverlay.test.ts

@@ -369,6 +369,37 @@ describe("useChatOverlay", () => {
     });
   });
 
+  describe("minimize/toggleMinimize guards", () => {
+    it("should not allow minimize when overlay is closed", () => {
+      const { result } = renderHook(() => useChatOverlay());
+
+      // Overlay starts closed
+      expect(result.current.isOpen).toBe(false);
+
+      act(() => {
+        result.current.minimize();
+      });
+
+      // Should remain unchanged - cannot minimize when closed
+      expect(result.current.isOpen).toBe(false);
+      expect(result.current.isMinimized).toBe(false);
+    });
+
+    it("should not allow toggleMinimize when overlay is closed", () => {
+      const { result } = renderHook(() => useChatOverlay());
+
+      expect(result.current.isOpen).toBe(false);
+
+      act(() => {
+        result.current.toggleMinimize();
+      });
+
+      // Should remain unchanged - cannot toggle minimize when closed
+      expect(result.current.isOpen).toBe(false);
+      expect(result.current.isMinimized).toBe(false);
+    });
+  });
+
   describe("storage error handling", () => {
     it("should call onStorageError when localStorage save fails", () => {
       const onStorageError = vi.fn();

apps/web/src/hooks/useChatOverlay.ts

@@ -83,7 +83,12 @@ function saveState(
   try {
     window.localStorage.setItem(STORAGE_KEY, JSON.stringify(state));
   } catch (error) {
-    const errorName = error instanceof DOMException ? error.name : "UnknownError";
+    const errorName =
+      error instanceof DOMException
+        ? error.name
+        : error instanceof Error
+          ? error.constructor.name
+          : "UnknownError";
     console.warn("Failed to save chat overlay state to localStorage:", error);
 
     if (onStorageError && !notifiedErrors.has(errorName)) {
@@ -119,7 +124,7 @@ export function useChatOverlay(options: UseChatOverlayOptions = {}): UseChatOver
   }, []);
 
   const minimize = useCallback(() => {
-    setState((prev) => ({ ...prev, isMinimized: true }));
+    setState((prev) => (prev.isOpen ? { ...prev, isMinimized: true } : prev));
   }, []);
 
   const expand = useCallback(() => {
@@ -134,7 +139,7 @@ export function useChatOverlay(options: UseChatOverlayOptions = {}): UseChatOver
   }, []);
 
   const toggleMinimize = useCallback(() => {
-    setState((prev) => ({ ...prev, isMinimized: !prev.isMinimized }));
+    setState((prev) => (prev.isOpen ? { ...prev, isMinimized: !prev.isMinimized } : prev));
   }, []);
 
   return {