fix: handle 404 errors for deleted assistant conversations

When a stored conversation ID no longer exists (e.g., database was reset
or conversation was deleted), the UI would repeatedly try to fetch it,
causing endless 404 errors in the console.

This fix:
- Stops retrying on 404 errors (conversation doesn't exist)
- Automatically clears the stored conversation ID from localStorage
  when a 404 is received, allowing the user to start fresh

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/components/AssistantPanel.tsx

@@ -49,11 +49,19 @@ export function AssistantPanel({ projectName, isOpen, onClose }: AssistantPanelP
   )
 
   // Fetch conversation details when we have an ID
-  const { data: conversationDetail, isLoading: isLoadingConversation } = useConversation(
+  const { data: conversationDetail, isLoading: isLoadingConversation, error: conversationError } = useConversation(
     projectName,
     conversationId
   )
 
+  // Clear stored conversation ID if it no longer exists (404 error)
+  useEffect(() => {
+    if (conversationError && conversationId) {
+      console.warn(`Conversation ${conversationId} not found, clearing stored ID`)
+      setConversationId(null)
+    }
+  }, [conversationError, conversationId])
+
   // Convert API messages to ChatMessage format for the chat component
   const initialMessages: ChatMessage[] | undefined = conversationDetail?.messages.map((msg) => ({
     id: `db-${msg.id}`,

ui/src/hooks/useConversations.ts

@@ -26,6 +26,13 @@ export function useConversation(projectName: string | null, conversationId: numb
     queryFn: () => api.getAssistantConversation(projectName!, conversationId!),
     enabled: !!projectName && !!conversationId,
     staleTime: 30_000, // Cache for 30 seconds
+    retry: (failureCount, error) => {
+      // Don't retry on 404 errors (conversation doesn't exist)
+      if (error instanceof Error && error.message.includes('404')) {
+        return false
+      }
+      return failureCount < 3
+    },
   })
 }