Feature: /fork to open parallel session seeded with current context #8482

Problem

When I’m working in a Codex CLI chat session (session A), I frequently get an idea or uncover a related sub-problem that I want to explore in parallel (session B) without interrupting my current flow.

In these cases, Codex needs the context from session A to be effective in session B (the codebase state, decisions already made, constraints, errors seen, etc.).

Current workaround

Start a new Codex instance and manually pass the session ID of session A to seed context (e.g., using the resume/session-id flow). This is non-obvious, breaks momentum, and makes parallel work feel clunky.

Feature request

Add a first-class way to “fork” the current session into a new parallel session that automatically inherits the relevant context from session A.

Proposed UX

• /fork → open a new parallel Codex session seeded with the current session’s context/history
• Optional flags (examples):
  • /fork --title "Investigate alternative fix"
  • /fork --summary (seed with an auto-summary instead of full transcript)
  • /fork --last N (seed with last N turns)
  • /fork --fresh (open parallel session without seeding)

The command should print the new session ID and a clear hint for switching/attaching.

Expected behavior

• The forked session starts immediately with inherited context (configurable: full transcript vs summary/last-N).
• Both sessions proceed independently after the fork.
• Discoverable via help/docs.

Why this matters

This would significantly improve UX for multitasking and exploratory workflows (debugging, “what if” investigations, docs, refactors) while keeping Codex effective by preserving the context it needs.