fix(web-ui): surface agent-level errors in chat UI

web-ui/src/components/chat/ChatPanel.tsx

@@ -99,14 +99,14 @@
     if (chatSessionId && chatSessionId !== sessionId) {
       setSessionId(chatSessionId)
     }
   }, [chatSessionId])
 
   const [configLoaded, setConfigLoaded] = useState(false)
   const messagesEndRef = useRef<HTMLDivElement>(null)
   const scrollContainerRef = useRef<HTMLDivElement>(null)
   const shouldAutoScroll = useRef(true)
   const textareaRef = useRef<HTMLTextAreaElement>(null)
   const mentionPopupRef = useRef<{ _handleKeyDown?: (e: KeyboardEvent) => boolean } | null>(null)
   const abortControllerRef = useRef<AbortController | null>(null)
   const reconnectingRef = useRef(false)
   const messagesRef = useRef(messages)
@@ -300,7 +300,7 @@
       }
     }
     if (auth.isAuthenticated) loadHistory()
   }, [sessionId, auth.isAuthenticated])
 
   // Reconnect to running background session (Local mode)
   // Uses EventSource with Last-Event-ID for seamless SSE resume.
@@ -466,7 +466,7 @@
       setAllDecks(data.decks)
     }
     if (auth.isAuthenticated) loadDecks()
   }, [auth.isAuthenticated])
 
   useEffect(() => {
     if (shouldAutoScroll.current) {
@@ -518,7 +518,7 @@
       })
 
     setMentionItems(items)
   }, [slidePreviewUrls, allDecks, deckId])
 
   /**
    * Handle file selection from + menu or drag-and-drop.
@@ -892,11 +892,21 @@
       if (err instanceof DOMException && err.name === "AbortError") {
         // Keep partial response as-is
       } else {
+        const errorMessage = err instanceof Error ? err.message : String(err)
+        const isRetryable = errorMessage.includes("ThrottlingException") || errorMessage.includes("throttl")
+          || errorMessage.includes("timed out") || errorMessage.includes("timeout")
+          || errorMessage.includes("not ready") || errorMessage.includes("ServiceUnavailable")
+        const isConversationLimit = errorMessage.includes("Too much media") || errorMessage.includes("too long")
+        const displayMessage = isConversationLimit
+          ? "This conversation is too long for the model to process. Please start a new chat to continue."
+          : isRetryable
+            ? "The service is temporarily busy or timed out. Please wait a moment and try again."
+            : "Sorry, something went wrong. Please try again."
         setMessages((prev) => {
           const updated = [...prev]
           updated[updated.length - 1] = {
             ...updated[updated.length - 1],
-            content: "Sorry, something went wrong. Please try again.",
+            content: displayMessage,
           }
           return updated
         })

web-ui/src/services/strandsParser.js

@@ -50,6 +50,28 @@ export const parseStreamingChunk = (line, currentCompletion, updateCallback, too
     // Keep-alive
     if (json.keepalive) return currentCompletion;
 
+    // Agent-level error (e.g. Bedrock ValidationException, image/token limit exceeded)
+    if (json.status === 'error' && json.error) {
+      const msg = json.error;
+      let errorMessage;
+      if (msg.includes("Too much media") || msg.includes("too long")) {
+        errorMessage = "⚠️ This conversation is too long for the model to process. Please start a new chat to continue.";
+      } else if (msg.includes("ThrottlingException") || msg.includes("throttl")) {
+        errorMessage = "⚠️ The service is temporarily busy. Please wait a moment and try again.";
+      } else if (msg.includes("ModelTimeoutException") || msg.includes("timed out") || msg.includes("timeout")) {
+        errorMessage = "⚠️ The model took too long to respond. Please try again.";
+      } else if (msg.includes("ModelNotReadyException") || msg.includes("not ready")) {
+        errorMessage = "⚠️ The model is not ready yet. Please wait a moment and try again.";
+      } else if (msg.includes("ServiceUnavailable")) {
+        errorMessage = "⚠️ The service is temporarily unavailable. Please try again later.";
+      } else {
+        errorMessage = `⚠️ ${msg}`;
+      }
+      const newCompletion = currentCompletion + errorMessage;
+      updateCallback(newCompletion);
+      return newCompletion;
+    }
+
     // MCP status event — pass to toolCallback with special type
     if (json.mcp_status) {
       if (toolCallback) toolCallback('__mcp_status__', { mcpStatus: json.mcp_status });