Do not clone live agents into session forks

Status: accepted

A Conversation Fork or Worktree Fork starts with an empty addressable agent tree. Referenced child transcript files before the selected point may be copied as read-only historical artifacts, but retained agent identities, mailboxes, conversations, configuration snapshots, and active turns are not cloned. The Source session and tree remain unchanged, and canonical task names are available for fresh agents in the child.

Rewind creates no child session. It clears live agent ownership in the current session because retained agents have no trustworthy per-turn journal. This avoids inventing a globally consistent snapshot across asynchronous conversations or importing agent work performed after the selected point.