diff --git a/backend/ai-core/internal/background/thinker.go b/backend/ai-core/internal/background/thinker.go
index 2ce7955..7f2f57b 100644
--- a/backend/ai-core/internal/background/thinker.go
+++ b/backend/ai-core/internal/background/thinker.go
@@ -524,11 +524,14 @@ func (t *Thinker) restoreContext() {
 			latest = m.CreatedAt
 		}
 	}
-	if !latest.IsZero() {
+	// Only use if reasonably recent (within 24h). Old memories don't represent user activity.
+	if !latest.IsZero() && time.Since(latest) < 24*time.Hour {
 		t.mu.Lock()
 		t.lastUserMessage = latest
 		t.mu.Unlock()
 		log.Printf("[后台思考] 上下文已恢复: 最近活动 %v 前", time.Since(latest).Round(time.Second))
+	} else if !latest.IsZero() {
+		log.Printf("[后台思考] 上下文恢复跳过: 最近记忆 %v 前(>24h)，使用默认值", time.Since(latest).Round(time.Second))
 	}
 }