Add explicit no-prune retention mode for archived local sessions

What variant of Codex are you using?

CLI

What feature would you like to see?

Add an explicit retention policy for local session rollouts, including a disabled/unlimited mode that guarantees Codex will not automatically delete or prune archived or old session files. The policy should keep lightweight history.jsonl retention separate from full rollout retention under $CODEX_HOME/sessions and $CODEX_HOME/archived_sessions. If cleanup is opt-in, document the scope clearly and make age/size-based cleanup explicit and reversible where possible.

Additional information

Observed on Codex CLI 0.147.0 on macOS. The documented history settings cover history.jsonl (history.persistence and history.max_bytes), but there is no documented setting for full archived rollout retention. codex doctor reports active and archived rollout stores separately. Affected thread ID: 019fdbfa-01d9-7811-ab79-14669e54f3a2. Related issues: #6015, #28187, and #37216.