fix: generate distinct task collaboration titles

Use verified task names until Agent generates a specific conversation title.
Repair legacy names without changing manual titles or history ordering.
Bound page repairs to 30 entries and a shared two-second deadline, and
re-read titles after task access validation to avoid stale reuse receipts.

Validation: bun run check; 40 focused tests across six files.

tests/routes/chatSession.test.ts

@@ -81,6 +81,26 @@ describe("shouldGenerateSessionTitle", () => {
 });
 
 describe("generateSessionTitle", () => {
+  it("uses the task name to distinguish collaboration titles and keeps it when generation is empty", async () => {
+    let titlePrompt = "";
+    let generatedTitle = "南桥爆管现场采样核对";
+    const runtime = {
+      createSession: async () => ({ id: "title-session" }),
+      prompt: async (_id: string, prompt: string) => { titlePrompt = prompt; },
+      waitForSessionIdle: async () => undefined,
+      messages: async () => [{ info: { role: "assistant" }, parts: [{ type: "text", text: generatedTitle }] }],
+      removeSession: async () => undefined,
+    } as unknown as OpencodeRuntimeAdapter;
+    const input = { sessionId: "collaboration-session", latestUserMessage: "目前进展如何？",
+      latestAssistantMessage: "等待现场采样核对。", taskTitle: "南桥管道爆管调查", fallbackTitle: "南桥管道爆管调查" };
+    expect(await generateSessionTitle(runtime, input)).toBe("南桥爆管现场采样核对");
+    expect(titlePrompt).toContain("关联任务：南桥管道爆管调查");
+    expect(titlePrompt).toContain("用户：目前进展如何？");
+    generatedTitle = "";
+    expect(await generateSessionTitle(runtime, input)).toBe("南桥管道爆管调查");
+    generatedTitle = "任务协作";
+    expect(await generateSessionTitle(runtime, input)).toBe("南桥管道爆管调查");
+  });
   it("uses the current user and assistant turn instead of reading wrapped runtime context", async () => {
     let titlePrompt = "";
     const runtime = {