test(server): wait for engine run completion in E3 instead of asserting immediately

The business row settles before the engine marks the workflow completed; under CI load the
window is a few hundred ms and the direct assertion flaked.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/server/test/e2e/e3-background-continues.test.ts

@@ -62,8 +62,16 @@ describe.skipIf(!hasPg)("E3 关闭聊天不影响后台", () => {
     );
     expect(run.finished_at).not.toBeNull();
     expect(run.summary).toContain("已入库 1 个");
-    const engineRun = await e.booted.ctx.engine.get(task.engine_run_id!);
-    expect(engineRun?.status).toBe("completed");
+    // 业务表先落终态,引擎在最后一步返回后才把 run 标 completed:给这个窗口留时间(负载高时会有几百毫秒)
+    const engineRun = await waitFor(
+      async () => {
+        const r = await e.booted.ctx.engine.get(task.engine_run_id!);
+        return r?.status === "completed" ? r : null;
+      },
+      15_000,
+      "engine run completed",
+    );
+    expect(engineRun.status).toBe("completed");
     const t = await e.db.selectFrom("task").select("status").where("id", "=", task.id).executeTakeFirstOrThrow();
     expect(t.status).toBe("succeeded");
     const slot = await e.db