Inbound hook to resume Codex session on external events

What feature would you like to see?

Add an inbound notification/resume mechanism so a Codex session can be re-prompted automatically when an external event finishes (e.g., training run completes). This would complement the existing outbound notify hook by allowing a small payload to resume the same session.

Suggested capabilities:

• Agent-authored inbound tool/script (or listener) that injects a follow-up message into the same session
• Session routing by session/thread/turn ID so multiple agents can run simultaneously
• Simple local transport (socket/pipe or codex --listen + codex --resume --session <id> --input <file|stdin>)
• Opt-in, local-only by default, with allowlist/token for security

Additional information

A minimal version could be notify_in = ["/path/to/script"] or codex listen with a JSON envelope {session_id, text, metadata}. I'm interested in contributing, especially inbound hook + session routing.