Preserve partial creation replies on stream failure

src/components/platform-entry/usePlatformCreationAgentFlowController.ts

@@ -1,4 +1,4 @@
-import { useCallback, useState } from 'react';
+import { useCallback, useRef, useState } from 'react';
 
 import type { TextStreamOptions } from '../../services/aiTypes';
 import type { SelectionStage } from './platformEntryTypes';
@@ -104,6 +104,16 @@ function buildOptimisticMessage<TMessagePayload extends CreationAgentMessageLike
   };
 }
 
+function buildInterruptedAssistantMessage(text: string) {
+  return {
+    id: `assistant-interrupted-${Date.now().toString(36)}`,
+    role: 'assistant',
+    kind: 'warning',
+    text: text.trim(),
+    createdAt: new Date().toISOString(),
+  };
+}
+
 /**
  * 轻量作品 Agent 创作流程的通用前端控制器。
  * 这里只处理跨玩法一致的会话、流式消息、忙碌态与草稿恢复，玩法结果页和运行态动作留给外层。
@@ -130,6 +140,18 @@ export function usePlatformCreationAgentFlowController<
   const [isBusy, setIsBusy] = useState(false);
   const [streamingReplyText, setStreamingReplyText] = useState('');
   const [isStreamingReply, setIsStreamingReply] = useState(false);
+  const latestStreamingReplyTextRef = useRef('');
+
+  const updateStreamingReplyText = useCallback((text: string) => {
+    latestStreamingReplyTextRef.current = text;
+    setStreamingReplyText(text);
+  }, []);
+
+  const resetStreamingReply = useCallback(() => {
+    latestStreamingReplyTextRef.current = '';
+    setStreamingReplyText('');
+    setIsStreamingReply(false);
+  }, []);
 
   const openWorkspace = useCallback(async (createPayload?: TCreatePayload) => {
     if (isBusy) {
@@ -138,8 +160,7 @@ export function usePlatformCreationAgentFlowController<
 
     setIsBusy(true);
     setError(null);
-    setStreamingReplyText('');
-    setIsStreamingReply(false);
+    resetStreamingReply();
 
     try {
       const response = await options.client.createSession(
@@ -159,7 +180,7 @@ export function usePlatformCreationAgentFlowController<
     } finally {
       setIsBusy(false);
     }
-  }, [isBusy, options]);
+  }, [isBusy, options, resetStreamingReply]);
 
   const restoreDraft = useCallback(
     async (sessionId: string | null | undefined) => {
@@ -171,8 +192,7 @@ export function usePlatformCreationAgentFlowController<
 
       setIsBusy(true);
       setError(null);
-      setStreamingReplyText('');
-      setIsStreamingReply(false);
+      resetStreamingReply();
 
       try {
         const response = await options.client.getSession(normalizedSessionId);
@@ -194,7 +214,7 @@ export function usePlatformCreationAgentFlowController<
         setIsBusy(false);
       }
     },
-    [options],
+    [options, resetStreamingReply],
   );
 
   const submitMessage = useCallback(
@@ -206,7 +226,7 @@ export function usePlatformCreationAgentFlowController<
       const optimisticMessage = buildOptimisticMessage(payload);
 
       setError(null);
-      setStreamingReplyText('');
+      updateStreamingReplyText('');
       setIsStreamingReply(true);
       setSession((current) =>
         current
@@ -223,12 +243,28 @@ export function usePlatformCreationAgentFlowController<
           session.sessionId,
           payload,
           {
-            onUpdate: setStreamingReplyText,
+            onUpdate: updateStreamingReplyText,
           },
         );
         setSession(nextSession);
-        setStreamingReplyText('');
+        updateStreamingReplyText('');
       } catch (caughtError) {
+        const interruptedReplyText =
+          latestStreamingReplyTextRef.current.trim();
+        // 上游流可能在已经吐出可读回复后才失败；把这段回复落进本地消息列表，避免 UI 收尾时突然消失。
+        if (interruptedReplyText) {
+          const interruptedMessage =
+            buildInterruptedAssistantMessage(interruptedReplyText);
+          setSession((current) =>
+            current
+              ? {
+                  ...current,
+                  messages: [...current.messages, interruptedMessage],
+                  updatedAt: interruptedMessage.createdAt,
+                }
+              : current,
+          );
+        }
         setError(
           options.resolveErrorMessage(caughtError, options.errorMessages.submit),
         );
@@ -236,7 +272,7 @@ export function usePlatformCreationAgentFlowController<
         setIsStreamingReply(false);
       }
     },
-    [isStreamingReply, options, session],
+    [isStreamingReply, options, session, updateStreamingReplyText],
   );
 
   const executeAction = useCallback(
@@ -284,17 +320,15 @@ export function usePlatformCreationAgentFlowController<
 
   const leaveFlow = useCallback(() => {
     setError(null);
-    setStreamingReplyText('');
-    setIsStreamingReply(false);
+    resetStreamingReply();
     options.enterCreateTab();
     options.setSelectionStage(options.platformStage);
-  }, [options]);
+  }, [options, resetStreamingReply]);
 
   const resetTransientState = useCallback(() => {
     setError(null);
-    setStreamingReplyText('');
-    setIsStreamingReply(false);
-  }, []);
+    resetStreamingReply();
+  }, [resetStreamingReply]);
 
   return {
     session,