Operator decision for an unknown outcome or a context no checkpoint covers

Records an operator's decision where the platform will not guess: a turn whose outcome is unknown, or context no checkpoint covers. Nothing the execution did outside is reverted.

• abandon: the outcome_unknown turn target_turn_id becomes cancelled and its input receipt fails; the session is stopped.
• confirm_completed: with evidence_ref, the turn becomes completed and its input receipt succeeds; it needs a committed checkpoint that reaches the turn. The session is stopped.
• close: ends the session for good.
• start_fresh: continues on a new engine session that does not remember the turns before; the checkpoints so far are retired and queued input runs.
• retry_restore: restores the same checkpoint again after what made the restores fail is fixed; queued input runs.

The decision takes effect in the request: the receipt is succeeded in the response, with result {resulting_admission_state, checkpoint_revision, resumable}. After abandon or confirm_completed, resume the session; resumable: false means a resume would answer CHECKPOINT_UNAVAILABLE. The decision is also recorded as a system event on the stream.

Scope: sessions:recover (API key or cookie session). Idempotency-Key: required.