Allow active sessions to be moved into the background

What variant of Codex are you using?

CLI

What feature would you like to see?

Codex should let users background an active session at any point in its lifecycle and continue accessing it through codex agents.

Long-running tasks often need some initial user attention before they can proceed independently. At that point, users should be able to detach or “put this session in the
background,” switch their attention to another session, and return later without interrupting the work.

Currently, attempting this mid-session shows:

Shared agents unavailable
This session isn’t connected to a shared background server.

Starting the background server afterward does not migrate the existing session. Codex should support connecting an active session to the shared background server dynamically,
preserving its full state and any running work.

This is distinct from background Bash commands. The request is to detach and background the entire Codex agent session, including its conversation state and ongoing agent work, so the user can switch to another session and return later. Background command execution may support this workflow, but does not by itself make an active session available through codex agents.

Additional information

No response

The issue names no files or tests. Start by tracing the CLI session lifecycle and the shared background server used by codex agents, including how active sessions retain state and running work. Done means an active session can be backgrounded at any lifecycle point, remains accessible through codex agents, and can be resumed without losing state or work.