feat: agent proactively re-engages users on returning sessions

Two complementary changes to reduce conversation cold-start friction:

A. Returning-user re-greeting (backend)
- When WS reconnects to a non-empty conversation and last_message_at is older
  than chat_re_greeting_idle_hours (default 6h), the agent emits a warm
  continuation message that references prior history instead of staying silent.
- Self-debouncing: the AI message updates last_message_at, so reconnects
  within the window will not re-trigger.
- Skipped while profile collection is still pending.

D. Topic suggestion chips (backend + Expo)
- New WS message type topic_suggestions carries 3-4 quick-start chips derived
  from the current memoir stage's empty slots (deterministic, no extra LLM
  cost). Sent alongside opening / re-greeting / resume.
- Expo chat screen renders a horizontally-scrollable chip row above the input
  bar; tapping a chip sends the chip's text as a user message and clears the
  row. Sending any text/voice also clears the chips.

app-expo/src/app/(main)/conversation/[id].tsx

@@ -27,6 +27,7 @@ import {
   type NativeSyntheticEvent,
   Platform,
   Pressable,
+  ScrollView,
   StyleSheet,
   Text as RNText,
   TextInput,
@@ -50,6 +51,7 @@ import { useThemeColors } from '@/hooks/use-theme-colors';
 import { useTypography } from '@/core/typography-context';
 import { useMessages, useRealtimeSession } from '@/features/conversation/hooks';
 import type { TtsSegmentPayload } from '@/features/conversation/realtime-session';
+import type { TopicSuggestion } from '@/core/ws/types';
 import { conversationKeys } from '@/features/conversation/query-keys';
 import {
   assistantSegmentMessageId,
@@ -715,6 +717,58 @@ function VoiceRecordButton({
   );
 }
 
+function TopicChipsRow({
+  chips,
+  onPressChip,
+  onDismiss,
+  dismissLabel,
+}: {
+  chips: TopicSuggestion[];
+  onPressChip: (text: string) => void;
+  onDismiss: () => void;
+  dismissLabel: string;
+}) {
+  if (!chips || chips.length === 0) return null;
+  return (
+    <View style={styles.topicChipsRow}>
+      <ScrollView
+        horizontal
+        showsHorizontalScrollIndicator={false}
+        contentContainerStyle={styles.topicChipsScrollContent}
+        keyboardShouldPersistTaps="handled"
+      >
+        {chips.map((chip) => (
+          <Pressable
+            key={chip.id}
+            onPress={() => onPressChip(chip.text)}
+            style={({ pressed }) => [
+              styles.topicChip,
+              pressed && styles.topicChipPressed,
+            ]}
+            accessibilityRole="button"
+            accessibilityLabel={chip.label}
+          >
+            <Text style={styles.topicChipText} numberOfLines={1}>
+              {chip.label}
+            </Text>
+          </Pressable>
+        ))}
+        <Pressable
+          onPress={onDismiss}
+          style={({ pressed }) => [
+            styles.topicChipDismiss,
+            pressed && styles.topicChipPressed,
+          ]}
+          accessibilityRole="button"
+          accessibilityLabel={dismissLabel}
+        >
+          <Text style={styles.topicChipDismissText}>{dismissLabel}</Text>
+        </Pressable>
+      </ScrollView>
+    </View>
+  );
+}
+
 function ChatInputBar({
   value,
   onChangeText,
@@ -1171,6 +1225,8 @@ export default function ConversationScreen() {
     connectionState,
     streamingMessage,
     awaitingAssistantReply,
+    topicSuggestions,
+    dismissTopicSuggestions,
     sendText,
     sendVoiceMessage,
     sendTtsCancel,
@@ -1394,6 +1450,38 @@ export default function ConversationScreen() {
     scheduleRefocusComposer();
   };
 
+  const handleTopicChipPress = useCallback(
+    (chipText: string) => {
+      const text = chipText.trim();
+      if (!text) return;
+      if (connectionState === 'disconnected') {
+        Alert.alert(t('chatUnavailableTitle'), t('chatUnavailableDisconnected'));
+        return;
+      }
+      if (connectionState === 'connecting') {
+        pendingTextSendRef.current = text;
+        clearConnectingSendTimeout();
+        connectingSendTimeoutRef.current = setTimeout(() => {
+          connectingSendTimeoutRef.current = null;
+          if (pendingTextSendRef.current !== text) return;
+          pendingTextSendRef.current = null;
+          Alert.alert(t('chatUnavailableTitle'), t('chatQueueSendTimeout'));
+        }, CONNECTING_SEND_TIMEOUT_MS);
+        dismissTopicSuggestions();
+        return;
+      }
+      sendText(text);
+      dismissTopicSuggestions();
+    },
+    [
+      connectionState,
+      sendText,
+      dismissTopicSuggestions,
+      clearConnectingSendTimeout,
+      t,
+    ],
+  );
+
   /** 仅完全断开时禁用发送/语音；连接中可点发送（排队） */
   const composerDisabled = connectionState === 'disconnected';
 
@@ -1533,6 +1621,12 @@ export default function ConversationScreen() {
             </Text>
           </View>
         ) : null}
+        <TopicChipsRow
+          chips={topicSuggestions}
+          onPressChip={handleTopicChipPress}
+          onDismiss={dismissTopicSuggestions}
+          dismissLabel={t('topicSuggestionsDismiss')}
+        />
         <ChatInputBar
           value={input}
           onChangeText={setInput}
@@ -1826,6 +1920,40 @@ const styles = StyleSheet.create({
     paddingHorizontal: 14,
     paddingVertical: 12,
   },
+  topicChipsRow: {
+    paddingTop: 10,
+    paddingBottom: 4,
+  },
+  topicChipsScrollContent: {
+    paddingHorizontal: 14,
+    gap: 8,
+    flexDirection: 'row',
+    alignItems: 'center',
+  },
+  topicChip: {
+    paddingHorizontal: 14,
+    paddingVertical: 8,
+    borderRadius: 18,
+    backgroundColor: 'rgba(141, 140, 144, 0.14)',
+    borderWidth: StyleSheet.hairlineWidth,
+    borderColor: 'rgba(141, 140, 144, 0.24)',
+  },
+  topicChipPressed: {
+    opacity: 0.6,
+  },
+  topicChipText: {
+    fontSize: 14,
+    color: CHAT_COLORS.onSurface,
+  },
+  topicChipDismiss: {
+    paddingHorizontal: 12,
+    paddingVertical: 8,
+    borderRadius: 18,
+  },
+  topicChipDismissText: {
+    fontSize: 13,
+    color: 'rgba(60, 60, 67, 0.6)',
+  },
   iconButton: {
     width: 44,
     height: 44,

app-expo/src/core/ws/client.ts

@@ -59,6 +59,28 @@ function mapServerMessage(raw: RawServerMessage): WsEvent | null {
     case 'memoir_update':
       return { kind: 'memoir_updated', conversationId: cid, data: d };
 
+    case 'topic_suggestions': {
+      const rawSuggestions = Array.isArray(d.suggestions) ? d.suggestions : [];
+      const suggestions = rawSuggestions
+        .map((raw) => {
+          if (!raw || typeof raw !== 'object') return null;
+          const s = raw as Record<string, unknown>;
+          const id = typeof s.id === 'string' ? s.id : '';
+          const label = typeof s.label === 'string' ? s.label : '';
+          const text = typeof s.text === 'string' ? s.text : '';
+          if (!id || !label || !text) return null;
+          return { id, label, text };
+        })
+        .filter((x): x is { id: string; label: string; text: string } => !!x);
+      return {
+        kind: 'topic_suggestions',
+        conversationId: cid,
+        reason: typeof d.reason === 'string' ? d.reason : '',
+        stage: typeof d.stage === 'string' ? d.stage : undefined,
+        suggestions,
+      };
+    }
+
     case 'error':
       return {
         kind: 'session_error',

app-expo/src/core/ws/types.ts

@@ -7,6 +7,7 @@ export type ServerMessageType =
   | 'tts_audio'
   | 'end_conversation'
   | 'memoir_update'
+  | 'topic_suggestions'
   | 'error';
 
 export type ClientMessageType =
@@ -81,6 +82,22 @@ export interface MemoirUpdatedEvent {
   data: Record<string, unknown>;
 }
 
+export interface TopicSuggestion {
+  id: string;
+  label: string;
+  /** 用户点击后作为用户文本发送的内容 */
+  text: string;
+}
+
+export interface TopicSuggestionsEvent {
+  kind: 'topic_suggestions';
+  conversationId: string;
+  /** 触发原因：opening | re_greeting | resume */
+  reason: string;
+  stage?: string;
+  suggestions: TopicSuggestion[];
+}
+
 export interface SessionErrorEvent {
   kind: 'session_error';
   conversationId: string;
@@ -96,6 +113,7 @@ export type WsEvent =
   | TtsAudioReceivedEvent
   | ConversationEndedEvent
   | MemoirUpdatedEvent
+  | TopicSuggestionsEvent
   | SessionErrorEvent;
 
 // ─── Connection state ───

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

@@ -2,7 +2,7 @@ import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { File, Paths } from 'expo-file-system';
 import { useCallback, useEffect, useRef, useState } from 'react';
 
-import type { WsConnectionState } from '@/core/ws/types';
+import type { TopicSuggestion, WsConnectionState } from '@/core/ws/types';
 
 import { conversationApi } from './api';
 import { conversationMessagesRepository } from './conversation-messages-repository';
@@ -183,6 +183,9 @@ interface RealtimeSessionState {
   /** 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;
+  /** 服务端下发的 quick-start 话题 chips；用户首次发文本/语音后清空 */
+  topicSuggestions: TopicSuggestion[];
+  dismissTopicSuggestions: () => void;
   sendText: (text: string) => void;
   sendVoiceMessage: (uri: string, durationMs: number) => Promise<boolean>;
   sendEndConversation: () => void;
@@ -204,6 +207,9 @@ export function useRealtimeSession({
     useState<StreamingAgentMessage | null>(null);
   const [awaitingAssistantReply, setAwaitingAssistantReply] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  const [topicSuggestions, setTopicSuggestions] = useState<TopicSuggestion[]>(
+    [],
+  );
 
   const handleStreamingText: StreamingTextCallback = useCallback(
     (text, isComplete) => {
@@ -225,6 +231,17 @@ export function useRealtimeSession({
     setError(message);
   }, []);
 
+  const handleTopicSuggestions = useCallback(
+    (payload: { suggestions: TopicSuggestion[] }) => {
+      setTopicSuggestions(payload.suggestions);
+    },
+    [],
+  );
+
+  const dismissTopicSuggestions = useCallback(() => {
+    setTopicSuggestions([]);
+  }, []);
+
   useEffect(() => {
     if (!enabled || !conversationId) return;
 
@@ -233,6 +250,7 @@ export function useRealtimeSession({
       queryClient,
       onStreamingText: handleStreamingText,
       onTtsSegment,
+      onTopicSuggestions: handleTopicSuggestions,
       onError: handleError,
       onStateChange: setConnectionState,
     });
@@ -246,6 +264,7 @@ export function useRealtimeSession({
       setConnectionState('disconnected');
       setStreamingMessage(null);
       setAwaitingAssistantReply(false);
+      setTopicSuggestions([]);
     };
   }, [
     conversationId,
@@ -253,6 +272,7 @@ export function useRealtimeSession({
     queryClient,
     handleStreamingText,
     handleError,
+    handleTopicSuggestions,
     onTtsSegment,
   ]);
 
@@ -267,6 +287,7 @@ export function useRealtimeSession({
       }
 
       setAwaitingAssistantReply(true);
+      setTopicSuggestions([]);
       onTtsPlaybackResume?.();
 
       const localId = `pending_${Date.now()}`;
@@ -326,6 +347,7 @@ export function useRealtimeSession({
         }
 
         setAwaitingAssistantReply(true);
+        setTopicSuggestions([]);
         const localId = `pending_voice_${Date.now()}`;
         await voiceSegmentStore.recordSentSegment({
           voiceSessionId,
@@ -385,6 +407,8 @@ export function useRealtimeSession({
     streamingMessage,
     awaitingAssistantReply,
     error,
+    topicSuggestions,
+    dismissTopicSuggestions,
     sendText,
     sendVoiceMessage,
     sendEndConversation,

app-expo/src/features/conversation/realtime-session.ts

@@ -5,7 +5,11 @@ import {
   type WsEventListener,
   type WsStateListener,
 } from '@/core/ws/client';
-import type { WsConnectionState, WsEvent } from '@/core/ws/types';
+import type {
+  TopicSuggestion,
+  WsConnectionState,
+  WsEvent,
+} from '@/core/ws/types';
 
 import { handleWsEvent } from './event-handlers';
 import { assistantSegmentMessageId, lastSegmentPreview } from './message-split';
@@ -14,6 +18,11 @@ import type { ConversationListItem, MessageItem } from './types';
 
 export type StreamingTextCallback = (text: string, isComplete: boolean) => void;
 export type ErrorCallback = (message: string, code?: string) => void;
+export type TopicSuggestionsCallback = (payload: {
+  reason: string;
+  stage?: string;
+  suggestions: TopicSuggestion[];
+}) => void;
 
 /** WebSocket `tts_audio`：服务端可能只带 base64、只带 COS URL，或两者都有 */
 export type TtsSegmentPayload = {
@@ -31,6 +40,8 @@ interface RealtimeSessionOptions {
   onStreamingText?: StreamingTextCallback;
   /** 收到 TTS 片段时入队播放（与「气泡上的手动朗读按钮」无关） */
   onTtsSegment?: (payload: TtsSegmentPayload) => void;
+  /** 服务端下发 quick-start 话题 chips 时回调；用户点击后调 sendText */
+  onTopicSuggestions?: TopicSuggestionsCallback;
   onError?: ErrorCallback;
   onStateChange?: WsStateListener;
 }
@@ -52,6 +63,7 @@ export class RealtimeSession {
   private queryClient: QueryClient;
   private onStreamingText?: StreamingTextCallback;
   private onTtsSegment?: (payload: TtsSegmentPayload) => void;
+  private onTopicSuggestions?: TopicSuggestionsCallback;
   private onError?: ErrorCallback;
   private unsubEvent: (() => void) | null = null;
   private unsubState: (() => void) | null = null;
@@ -66,6 +78,7 @@ export class RealtimeSession {
     this.queryClient = options.queryClient;
     this.onStreamingText = options.onStreamingText;
     this.onTtsSegment = options.onTtsSegment;
+    this.onTopicSuggestions = options.onTopicSuggestions;
     this.onError = options.onError;
 
     this.unsubEvent = this.client.onEvent(this.handleEvent);
@@ -154,6 +167,15 @@ export class RealtimeSession {
       return;
     }
 
+    if (event.kind === 'topic_suggestions') {
+      this.onTopicSuggestions?.({
+        reason: event.reason,
+        stage: event.stage,
+        suggestions: event.suggestions,
+      });
+      return;
+    }
+
     handleWsEvent(this.queryClient, event);
 
     if (event.kind === 'session_error') {

app-expo/src/i18n/generated/resources.ts

@@ -99,6 +99,7 @@ interface Resources {
     switchToVoice: 'Switch to voice input';
     tapToEndRecording: 'Tap to end';
     tapToStartRecording: 'Tap to start recording';
+    topicSuggestionsDismiss: 'Hide';
     timeDaysAgo_one: '{{count}} day ago';
     timeDaysAgo_other: '{{count}} days ago';
     timeHoursAgo_one: '{{count}} hour ago';

app-expo/src/i18n/locales/en/conversation.json

@@ -37,6 +37,7 @@
   "switchToVoice": "Switch to voice input",
   "tapToEndRecording": "Tap to end",
   "tapToStartRecording": "Tap to start recording",
+  "topicSuggestionsDismiss": "Hide",
   "viewAll": "View All",
   "voiceMessagePreview": "Voice message",
   "timeJustNow": "Just now",

app-expo/src/i18n/locales/zh/conversation.json

@@ -37,6 +37,7 @@
   "switchToVoice": "切换到语音输入",
   "tapToEndRecording": "点击结束",
   "tapToStartRecording": "点击开始录音",
+  "topicSuggestionsDismiss": "收起",
   "viewAll": "查看全部",
   "voiceMessagePreview": "语音消息",
   "timeJustNow": "刚刚",