Subagents

A subagent is a child fx session controlled by another agent. It uses the same workspace and runtime, with its own model, reasoning effort, permission mode, transcript, and lifecycle.

Run modes

A one-off child runs one prompt and finishes.
A persistent child returns to idle after each turn and can receive more messages.

Persistent children remain resumable fx sessions. Parent and child messages are queued durably, so the child can work without copying its full transcript into the parent's context.

ctrl+x manager

Press ctrl+x in an interactive session to open the manager. It can:

show the child tree and current state
create and open persistent children
send follow-up instructions
change name, model, effort, permission mode, and notifications
attach, detach, or reparent an existing session
resume, cancel, close, or reopen a child
resolve child approval requests

Closing the manager does not stop persistent children.

Agent tool

The model uses one subagent tool with six branches:

Branch	Purpose
`create`	Create a one-off or persistent child.
`inspect`	Read selected state for a child ID.
`message`	Send a parent message or emit a child milestone.
`relationship`	Attach, detach, or reparent a session.
`configure`	Change model, effort, permissions, name, or notifications.
`lifecycle`	Resume, cancel, close, or reopen a child.

Create a persistent child:

{
  "command": {
    "create": {
      "name": "researcher",
      "mode": "persistent",
      "prompt": "Inspect the authentication flow and report risky edges.",
      "model": "<provider/model-id>",
      "effort": "high",
      "permission_mode": "ask"
    }
  }
}

Operations use durable identities, so a safe retry returns the original result instead of repeating the effect.

Children cannot elevate model-created authority

When the model creates a child without specifying a permission mode, the child inherits the caller's effective permission mode and cannot request broader authority. A human-created child in the ctrl+x manager can use the manager's explicit configuration and may default to yolo, so review that setting before starting it.