fix(chat): restore forked context

tests/routes/chatSession.test.ts

@@ -4,6 +4,7 @@ import {
   buildPromptWithLearningContext,
   extractLatestFrontendTurn,
   generateSessionTitle,
+  shouldRestoreConversationForRuntime,
   shouldGenerateSessionTitle,
 } from "../../src/routes/chatSession.js";
 import { type SessionTurnRecord } from "../../src/sessions/transcriptStore.js";
@@ -161,6 +162,21 @@ describe("buildPromptWithLearningContext", () => {
     expect(prompt).not.toContain("[Previous conversation context]");
     expect(prompt).toBe("基于刚才结果继续分析");
   });
+
+  it("restores copied fork context when metadata exists but runtime has no conversation", () => {
+    expect(
+      shouldRestoreConversationForRuntime({
+        hadExistingSessionRecord: true,
+        runtimeHasConversation: false,
+      }),
+    ).toBe(true);
+    expect(
+      shouldRestoreConversationForRuntime({
+        hadExistingSessionRecord: true,
+        runtimeHasConversation: true,
+      }),
+    ).toBe(false);
+  });
 });
 
 describe("extractLatestFrontendTurn", () => {