feat: Show agent errors in chat UI with retry button

When the chat agent crashes (e.g., expired OAuth token), display the
error message inline with a Retry button that re-sends the last user
message. Input stays enabled so users can also send a new message.

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

@@ -1,6 +1,7 @@
 import { useEffect, useRef } from 'react';
 import { motion, AnimatePresence } from 'motion/react';
-import { X, Loader2 } from 'lucide-react';
+import { X, Loader2, AlertTriangle, RotateCcw } from 'lucide-react';
+import { Button } from '@/components/ui/button';
 import { useChatSession } from '@/hooks/useChatSession';
 import { ChatBubble } from './ChatBubble';
 import { ChatInput } from './ChatInput';
@@ -41,7 +42,7 @@ function ChatSlideOverInner({
   initiativeId: string;
   onClose: () => void;
 }) {
-  const { messages, agentStatus, sendMessage, closeSession, isSending } =
+  const { messages, agentStatus, agentError, sendMessage, closeSession, isSending } =
     useChatSession(target.type, target.id, initiativeId);
 
   const scrollRef = useRef<HTMLDivElement>(null);
@@ -130,6 +131,32 @@ function ChatSlideOverInner({
               </div>
             </div>
           )}
+          {agentStatus === 'crashed' && agentError && (
+            <div className="mx-4 my-2 rounded-lg border border-status-error-border bg-status-error-bg px-3 py-2.5">
+              <div className="flex items-start gap-2">
+                <AlertTriangle className="mt-0.5 h-3.5 w-3.5 shrink-0 text-status-error-fg" />
+                <div className="min-w-0 flex-1">
+                  <p className="text-xs font-medium text-status-error-fg">Agent error</p>
+                  <p className="mt-0.5 text-xs text-status-error-fg/80 break-words">{agentError}</p>
+                </div>
+              </div>
+              <div className="mt-2 flex justify-end">
+                <Button
+                  variant="outline"
+                  size="sm"
+                  className="h-6 gap-1.5 text-xs"
+                  onClick={() => {
+                    // Re-send the last user message to retry
+                    const lastUserMsg = [...messages].reverse().find(m => m.role === 'user');
+                    if (lastUserMsg) sendMessage(lastUserMsg.content);
+                  }}
+                >
+                  <RotateCcw className="h-3 w-3" />
+                  Retry
+                </Button>
+              </div>
+            </div>
+          )}
         </div>
 
         {/* Input */}

apps/web/src/hooks/useChatSession.ts

@@ -3,7 +3,7 @@ import { toast } from 'sonner';
 import { trpc } from '@/lib/trpc';
 import { useLiveUpdates } from './useLiveUpdates';
 
-export type ChatAgentStatus = 'idle' | 'running' | 'waiting' | 'none';
+export type ChatAgentStatus = 'idle' | 'running' | 'waiting' | 'crashed' | 'none';
 
 export interface ChatMessage {
   id: string;
@@ -28,6 +28,7 @@ export interface UseChatSessionResult {
   session: ChatSession | null;
   messages: ChatMessage[];
   agentStatus: ChatAgentStatus;
+  agentError: string | null;
   sendMessage: (message: string) => void;
   closeSession: () => void;
   isSending: boolean;
@@ -88,11 +89,26 @@ export function useChatSession(
         return 'waiting';
       case 'idle':
         return 'idle';
+      case 'crashed':
+        return 'crashed';
       default:
         return 'none';
     }
   }, [session?.agentId, agentQuery.data]);
 
+  // Extract error message when agent crashed
+  const agentError = useMemo(() => {
+    if (agentStatus !== 'crashed' || !agentQuery.data) return null;
+    const result = (agentQuery.data as { result?: string }).result;
+    if (!result) return 'Agent crashed unexpectedly';
+    try {
+      const parsed = JSON.parse(result);
+      return parsed.message ?? result;
+    } catch {
+      return result;
+    }
+  }, [agentStatus, agentQuery.data]);
+
   // Send message mutation
   const sendMutation = trpc.sendChatMessage.useMutation({
     onSuccess: () => {
@@ -161,6 +177,7 @@ export function useChatSession(
     session,
     messages,
     agentStatus,
+    agentError,
     sendMessage,
     closeSession,
     isSending,