Fork Session

agent.fork_session() deep-copies an entire session into a new, independent session — every run is copied with a fresh run_id, under a fresh session_id. The source session is untouched. Use it to branch a whole conversation thread and explore a different direction without mutating the original.

This is the session-level sibling of run-level fork (see ../20_time_travel/):

	`fork=True`	`fork_session()`
Granularity	Run	Session
Result	new sibling run, same session	new session with copies of every run
Endpoint	`POST /runs/{run_id}/continue`	`POST /sessions/{session_id}/fork`
Lineage field	`run.forked_from_run_id`	`run.forked_from_session_id`

The verb is consistent across both: fork = diverge a copy; the suffix tells you what you're copying.

Example	What it shows
`01_fork_session.py`	`fork_session()` / `afork_session()` and the `forked_from_session_id` lineage across nested forks.

bash

.venvs/demo/bin/python cookbook/02_agents/21_fork_session/01_fork_session.py