feat(lessons): convergence is named at the write — no-rule lessons that keep landing in one situation suggest a rule (milestone 440 step 5, #4634)

When a lesson is answered "no rule fits" (create_lesson / update_lesson on
both doors), the response looks for other no-rule lessons it resembles and,
once there are CONVERGENCE_LESSONS (3) of them, carries `convergence`: the
members, their incidents and projects, and a hint to draft the missing rule
with create_rule (operator approval as always) and point each lesson at it —
or to leave them as lessons when no single choice is right every time.

- convergence_group is the pure bar: distinct LESSONS count, incidents never
  stand in for them (one broad lesson cannot trigger it), and a group whose
  sources all point at one incident is one event written up several times.
- convergence_for searches lessons by the new one's claim + trigger
  (trigger_title) at CONVERGENCE_THRESHOLD 0.65 — above the menu's "worth
  showing", below the duplicate gate's "same record" — then keeps the ones
  with a lesson_no_rule answer. Fail-open. No sweep, no timer (#4183).
- Defaults stated as defaults (rules 32, 115).
- Tests: the bar (pure), the search with stubs, the door, and the no-rule
  filter against Postgres; conftest stubs convergence_for for unit tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scribe/routes/lessons.py

@@ -188,6 +188,10 @@ async def create_lesson_route():
     elif no_rule:
         await lesson_rules_svc.set_no_rule(uid, note.id, no_rule)
     out = lessons_svc.lesson_to_dict(note)
+    if no_rule:
+        group = await lesson_rules_svc.convergence_for(uid, note.id)
+        if group:
+            out["convergence"] = group
     out["systems"] = [
         s.to_dict() for s in await systems_svc.list_record_systems(uid, note.id)
     ]
@@ -292,6 +296,12 @@ async def update_lesson_route(lesson_id: int):
         # may edit — it decides WHOSE reach the tagging uses (#47).
         await systems_svc.set_record_systems(uid, lesson_id, data["system_ids"])
     out = lessons_svc.lesson_to_dict(updated)
+    if no_rule:
+        # The same nudge the MCP door gives (#4634): this answer may complete
+        # a group of no-rule lessons in one situation.
+        group = await lesson_rules_svc.convergence_for(uid, lesson_id)
+        if group:
+            out["convergence"] = group
     out["systems"] = [
         s.to_dict()
         for s in await systems_svc.list_record_systems(owner_uid, lesson_id)