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.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);
       }