重构聊天会话标题管理，支持首轮对话更新

src/components/chat/chatStorage.ts

@@ -68,14 +68,6 @@ const toSessionSummary = (session: ChatSessionRecord): ChatSessionSummary => ({
   updatedAt: session.updatedAt,
 });
 
-const buildSessionTitle = (messages: Message[]) => {
-  const firstUserMessage = messages.find((message) => message.role === "user");
-  if (!firstUserMessage) return "新对话";
-  const title = firstUserMessage.content.replace(/\s+/g, " ").trim();
-  if (!title) return "新对话";
-  return title.length > 24 ? `${title.slice(0, 24)}...` : title;
-};
-
 const getDb = () =>
   openDB<ChatDB>(CHAT_DB_NAME, CHAT_DB_VERSION, {
     upgrade(db) {
@@ -170,7 +162,7 @@ const migrateLegacyLocalStorage = async () => {
   const now = Date.now();
   const sessionRecord: ChatSessionRecord = {
     id: createId(),
-    title: buildSessionTitle(legacyState.messages),
+    title: "新对话",
     createdAt: now,
     updatedAt: now,
     sessionId: legacyState.sessionId,
@@ -244,9 +236,8 @@ export const saveActiveChatState = async (
 
   const now = Date.now();
   const storageSessionId = state.storageSessionId ?? createId();
-  const computedTitle = buildSessionTitle(state.messages);
   const preferredTitle = state.title?.trim();
-  const finalTitle = preferredTitle || computedTitle;
+  const finalTitle = preferredTitle || existingSession?.title || "新对话";
   const nextRecord: ChatSessionRecord = {
     id: storageSessionId,
     title: finalTitle,
@@ -278,6 +269,26 @@ export const listChatSessions = async (): Promise<ChatSessionSummary[]> => {
     .map(toSessionSummary);
 };
 
+export const updateChatSessionTitle = async (
+  storageSessionId: string,
+  title: string,
+): Promise<void> => {
+  if (typeof window === "undefined") return;
+
+  const normalizedTitle = title.trim();
+  if (!normalizedTitle) return;
+
+  const db = await getDb();
+  const session = await db.get(SESSION_STORE, storageSessionId);
+  if (!session) return;
+
+  await db.put(SESSION_STORE, {
+    ...session,
+    title: normalizedTitle,
+    updatedAt: Date.now(),
+  });
+};
+
 export const createEmptyChatSession = async (): Promise<LoadedChatState> => {
   if (typeof window === "undefined") return emptyLoadedChatState();