fix(chat): keep stored rectification titles on open

Opening a saved birth-time session no longer restamps the title or updatedAt from the wall clock. Occupies BUG-699, recurrence of BUG-553.

frontend/src/hooks/use-rectification-surface.ts

@@ -3,6 +3,7 @@
 import type { Dispatch, MutableRefObject, SetStateAction } from "react";
 
 import { resolveSessionTitle } from "@/lib/agent-reply";
+import { rectificationOpenIdentity } from "@/lib/rectification-session-open";
 import { showChatNotice as setComposerNotice } from "@/lib/chat-notice";
 import { writeSessionUrl } from "@/lib/chat-session-url";
 import type { ConsultationEntrypoint } from "@/lib/consultation-entrypoint";
@@ -213,16 +214,20 @@ export function useRectificationSurface(params: RectificationSurfaceParams) {
       // Merge the server-created session into the local list. The browser
       // never generates a Case id; it only mirrors the returned binding.
       const existing = sessions.find((session) => session.id === opened.sessionId);
-      const merged: ChatSession = {
-        id: opened.sessionId,
+      const openIdentity = rectificationOpenIdentity(existing, {
         title: resolveSessionTitle("生时校正", undefined, {
           entrypoint: "birth_time_rectification",
           existingTitles: sessions.map((session) => session.title),
         }),
+        updatedAt: timestamp(),
+      });
+      const merged: ChatSession = {
+        id: opened.sessionId,
+        title: openIdentity.title,
         theme: "general",
         modelId: modelCatalog.defaultModelId ?? "",
         messages: [],
-        updatedAt: timestamp(),
+        updatedAt: openIdentity.updatedAt,
         sessionType: "birth_time_rectification",
         rectificationCaseId: opened.caseId,
         pinned: existing?.pinned ?? false,