diff --git a/internal/app.go b/internal/app.go
index 30ba2eb..ef43b65 100644
--- a/internal/app.go
+++ b/internal/app.go
@@ -191,10 +191,15 @@ func (m *Model) setUserTitle(sessionID, title string) tea.Cmd {
 		}
 	}
 	if m.history.Cache != nil {
-		if entry, ok := m.history.Cache[sessionID]; ok {
-			entry.UserTitle = title
-			m.cacheDirty = true
+		entry, ok := m.history.Cache[sessionID]
+		if !ok {
+			// 缓存缺 entry（如缓存文件损坏/新会话未入缓存）时补建，
+			// 否则标题只改内存不落盘，重启后丢失
+			entry = &cacheEntry{}
+			m.history.Cache[sessionID] = entry
 		}
+		entry.UserTitle = title
+		m.cacheDirty = true
 	}
 	// 调度落盘，避免改名只存在内存、被磁盘旧缓存覆盖
 	return cacheFlushTick()
diff --git a/internal/edit_title_test.go b/internal/edit_title_test.go
index 19aa043..154a4fe 100644
--- a/internal/edit_title_test.go
+++ b/internal/edit_title_test.go
@@ -98,4 +98,4 @@ func TestEditTitleInput(t *testing.T) {
 	if m.editTitleCursor != 0 {
 		t.Fatalf("esc 应重置光标, got %d", m.editTitleCursor)
 	}
-}
\ No newline at end of file
+}
diff --git a/internal/rename_persist_test.go b/internal/rename_persist_test.go
index 6d95b0b..2a12704 100644
--- a/internal/rename_persist_test.go
+++ b/internal/rename_persist_test.go
@@ -53,3 +53,23 @@ func TestRenameSurvivesStaleScan(t *testing.T) {
 		t.Fatalf("扫描后 session UserTitle 丢失: = %q, 期望 \"我的新名\"", s.UserTitle)
 	}
 }
+
+// TestSetUserTitleBackfillCacheEntry 验证缓存缺 entry 时（缓存文件损坏/
+// 新会话未入缓存）重命名会补建 entry，保证标题落盘而非只改内存
+func TestSetUserTitleBackfillCacheEntry(t *testing.T) {
+	m := NewModel()
+	m.history.Cache = map[string]*cacheEntry{}
+
+	m.setUserTitle("missing-session", "新标题")
+
+	e, ok := m.history.Cache["missing-session"]
+	if !ok {
+		t.Fatal("缓存缺 entry 时应补建")
+	}
+	if e.UserTitle != "新标题" {
+		t.Fatalf("补建 entry 应写入标题, got %q", e.UserTitle)
+	}
+	if !m.cacheDirty {
+		t.Fatal("应置 cacheDirty 调度落盘")
+	}
+}