Event-driven background task callbacks

What variant of Codex are you using?

CLI

What feature would you like to see?

Please allow Codex CLI to start a background process and return the session to idle. Waiting should require no model calls or token usage.

When the process exits, Codex should automatically notify and resume the original thread with its exit code and output. If another turn is active, the event can be queued until that turn finishes.

Desired flow:

Start background task → session becomes idle → zero-token waiting → task exits → original thread wakes up → Codex continues automatically

Claude Code references:

• Background Bash commands (https://code.claude.com/docs/en/interactive-mode#background-bash-commands)
• Scheduled tasks and Monitor (https://code.claude.com/docs/en/scheduled-tasks)
• Background task completion notifications (https://code.claude.com/docs/en/agent-sdk/python#tasknotificationmessage)

Additional information

_No response_