Phase 3.5 T83.4 surfaced un-rolled-back lifecycle transitions on
regenerate; T114 wires up the actual rollback. Step 1 is the back-
reference: every event_started / event_completed / event_cancelled
emitted by post_turn (chat/web/turns.py) and regenerate
(chat/services/regenerate.py) now carries
``triggered_by_assistant_turn_id`` in its payload, set to the id of
the assistant_turn event that produced the transition.
Schema decision (Option A from the plan): no migration. The field is
a payload convention only — older event_log rows lack it and rollback
will skip them with a debug log when T114.3 lands. Forward-only.
The post_turn lifecycle block already runs AFTER the assistant_turn
event is appended (step 8a vs step 7), so ``primary_assistant_event_id``
is in scope. Same for regenerate: the lifecycle classification (step 9a)
runs after step 6's append. **No emission-order reorder was needed**
in either flow.
Updates ``test_turn_with_event_transition_appends_started_event`` to
assert the new field is present in the emitted event_started payload
and points at the assistant_turn id.
Joseph Doherty
7370f68bdf