feat(memoir+conversation): 章节/故事最小可读字数；会话 hasUserMessage 与 UI 优化

- 后端：300 字门槛统一物化、hydrate、列表/PDF/详情；过短章节对读者隐藏
- 对话：首包前打字动画、大字模式排版、朗读/TTS 交互与布局稳定
- 首页：复用无用户消息会话；空列表「继续对话」与文案 i18n
- 章节阅读：标题进正文、封面与去重标题；阅读 Markdown 字号上调

app-expo/src/features/conversation/hooks.ts

@@ -65,6 +65,7 @@ export function useCreateConversation() {
             latestMessageTime: Date.now(),
             unreadCount: 0,
             isDefaultAssistant: true,
+            hasUserMessage: false,
           };
           return [item, ...(old ?? [])];
         },
@@ -134,6 +135,8 @@ function generateUUID(): string {
 interface RealtimeSessionState {
   connectionState: WsConnectionState;
   streamingMessage: StreamingAgentMessage | null;
+  /** 已发出用户消息，尚未收到助手首段流式文本（用于「正在回复」气泡） */
+  awaitingAssistantReply: boolean;
   error: string | null;
   sendText: (text: string) => void;
   sendVoiceMessage: (uri: string, durationMs: number) => Promise<boolean>;
@@ -154,12 +157,17 @@ export function useRealtimeSession({
     useState<WsConnectionState>('disconnected');
   const [streamingMessage, setStreamingMessage] =
     useState<StreamingAgentMessage | null>(null);
+  const [awaitingAssistantReply, setAwaitingAssistantReply] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
   const handleStreamingText: StreamingTextCallback = useCallback(
     (text, isComplete) => {
+      if (text.trim().length > 0) {
+        setAwaitingAssistantReply(false);
+      }
       if (isComplete) {
         setStreamingMessage(null);
+        setAwaitingAssistantReply(false);
         return;
       }
       setStreamingMessage({ text, isComplete });
@@ -168,6 +176,7 @@ export function useRealtimeSession({
   );
 
   const handleError: ErrorCallback = useCallback((message) => {
+    setAwaitingAssistantReply(false);
     setError(message);
   }, []);
 
@@ -191,6 +200,7 @@ export function useRealtimeSession({
       sessionRef.current = null;
       setConnectionState('disconnected');
       setStreamingMessage(null);
+      setAwaitingAssistantReply(false);
     };
   }, [
     conversationId,
@@ -211,6 +221,7 @@ export function useRealtimeSession({
         return;
       }
 
+      setAwaitingAssistantReply(true);
       onTtsPlaybackResume?.();
 
       const localId = `pending_${Date.now()}`;
@@ -229,6 +240,18 @@ export function useRealtimeSession({
           return [...(old ?? []), msg];
         },
       );
+
+      queryClient.setQueryData<ConversationListItem[]>(
+        conversationKeys.lists(),
+        (old) => {
+          if (!old) return old;
+          return old.map((item) =>
+            item.id === conversationId
+              ? { ...item, hasUserMessage: true }
+              : item,
+          );
+        },
+      );
     },
     [conversationId, queryClient, onTtsPlaybackResume],
   );
@@ -258,6 +281,7 @@ export function useRealtimeSession({
           return false;
         }
 
+        setAwaitingAssistantReply(true);
         const localId = `pending_voice_${Date.now()}`;
         await voiceSegmentStore.recordSentSegment({
           voiceSessionId,
@@ -282,6 +306,18 @@ export function useRealtimeSession({
             return [...(old ?? []), msg];
           },
         );
+
+        queryClient.setQueryData<ConversationListItem[]>(
+          conversationKeys.lists(),
+          (old) => {
+            if (!old) return old;
+            return old.map((item) =>
+              item.id === conversationId
+                ? { ...item, hasUserMessage: true }
+                : item,
+            );
+          },
+        );
         onTtsPlaybackResume?.();
         return true;
       } catch {
@@ -303,6 +339,7 @@ export function useRealtimeSession({
   return {
     connectionState,
     streamingMessage,
+    awaitingAssistantReply,
     error,
     sendText,
     sendVoiceMessage,