Real server MCP evidence | commit 23e418c94e2e1f0e60dc07f22a86f4b3c343b92e
Environment: Linux; isolated fresh database; synthetic project; deterministic ACP agent.
1. Parent calls delegate_task(mode="async"); child waits at an explicit release gate.
2. Parent turn ended; delegated child still running.
t3_thread_read: {
  "threadId": "mcp:5dcdecb4-82df-417e-a41c-32d9f7c8ed4c",
  "title": "Parent background work",
  "status": "completed",
  "activeRunId": null,
  "blockedOnThreadWait": false,
  "pendingBackgroundTasks": [
    {
      "taskId": "turn-item:delegated-task:command%3Amcp%3Af072980b-510b-45f9-9a8d-8c11af4cc97d%3Adelegate-task%3A8d9f9f05-dbca-4129-a7bc-2febc6f24819",
      "kind": "subagent",
      "description": "Pending child",
      "childThreadId": "thread:delegated-task:command%3Amcp%3Af072980b-510b-45f9-9a8d-8c11af4cc97d%3Adelegate-task%3A8d9f9f05-dbca-4129-a7bc-2febc6f24819"
    }
  ]
}
t3_thread_list (parent): {
  "threadId": "mcp:5dcdecb4-82df-417e-a41c-32d9f7c8ed4c",
  "title": "Parent background work",
  "status": "waiting",
  "blockedOnThreadWait": false,
  "pendingBackgroundTasks": [
    {
      "taskId": "turn-item:delegated-task:command%3Amcp%3Af072980b-510b-45f9-9a8d-8c11af4cc97d%3Adelegate-task%3A8d9f9f05-dbca-4129-a7bc-2febc6f24819",
      "kind": "subagent",
      "description": "Pending child",
      "childThreadId": "thread:delegated-task:command%3Amcp%3Af072980b-510b-45f9-9a8d-8c11af4cc97d%3Adelegate-task%3A8d9f9f05-dbca-4129-a7bc-2febc6f24819"
    }
  ]
}
Latest parent run status: completed
3. Release child and wait for the parent to handle its completion.
4. Same MCP calls after completion is handled.
t3_thread_read: {
  "threadId": "mcp:5dcdecb4-82df-417e-a41c-32d9f7c8ed4c",
  "title": "Parent background work",
  "status": "completed",
  "activeRunId": null,
  "blockedOnThreadWait": false,
  "pendingBackgroundTasks": []
}
t3_thread_list (parent): {
  "threadId": "mcp:5dcdecb4-82df-417e-a41c-32d9f7c8ed4c",
  "title": "Parent background work",
  "status": "completed",
  "blockedOnThreadWait": false,
  "pendingBackgroundTasks": []
}
Latest parent run status: completed