refactor: regenerate event-detection ordering mirrors post_turn (T83.5)

Cosmetic-only renumbering of the event-lifecycle detection block in
``regenerate_assistant_turn`` from ``# 10.`` to ``# 9a.`` — mirrors the
``# 8a.`` shape in ``chat.web.turns.post_turn``. The block was already
in the correct structural position (immediately after the interjection
branch); only the numbering and comment reflected an earlier draft
where it read as a final step rather than the post-interjection /
pre-(absent)-scene-close slot.

No behavioural change. All 9 regenerate tests + 18 turn_flow tests
pass without modification.

chat/services/regenerate.py

@@ -686,23 +686,28 @@ async def regenerate_assistant_turn(
                 (new_assistant_event_id, original_interjection_event_id),
             )
 
-    # 10. Event-lifecycle detection (Phase 3, T61). Mirrors the post_turn
-    # block: classify whether any active events transitioned in the
-    # regenerated narrative and append the corresponding event_started /
+    # 9a. Event-lifecycle detection (Phase 3, T61). T83.5 cosmetic
+    # ordering: mirrors ``chat.web.turns.post_turn``'s 8a block — runs
+    # AFTER the interjection branch (and AFTER the post-interjection
+    # state-update + memory passes) so the classifier sees the same
+    # narrative-text input post_turn does. Numbering uses ``9a`` to
+    # match post_turn's ``8a`` shape (the interjection branch is step 9
+    # in regenerate vs step 8 in post_turn; lifecycle is the immediate
+    # follow-on in both). Behaviour identical to the prior ``step 10``
+    # placement — the block was already structurally last in regenerate
+    # because there's no scene-close pass here.
+    #
+    # Classify whether any active events transitioned in the regenerated
+    # narrative and append the corresponding event_started /
     # event_completed / event_cancelled. ``promote_completed_event``
     # runs inline after a completion so promotion artifacts land in the
     # same regenerate path.
     #
-    # Phase 3.5 follow-up: when a regenerate replaces a turn that had
-    # already produced event transitions, those original transitions are
-    # NOT undone here. The superseded ``assistant_turn`` group keeps its
-    # prior ``event_started`` / ``event_completed`` events in the log
-    # (they remain projected onto the events table). Phase 3.5 will add
-    # an "undo lifecycle" step to roll back the prior transitions before
-    # re-classifying the regenerated text. For v3 we accept that a
-    # regenerate-after-completion will double-emit promotion artifacts
-    # if the new text re-completes the same event — narratively rare,
-    # and a true fix needs the lifecycle-undo pass.
+    # T83.4 follow-up: when a regenerate replaces a turn that had
+    # already produced event transitions, those original transitions
+    # are NOT undone here (Phase 4 work). A WARNING log earlier in this
+    # function names the affected event_log ids — see the T83.4 block
+    # near the function entry.
     new_active_events = list_active_events(conn, chat_id)
     if new_active_events:
         lifecycle_decision = await detect_event_transitions(