feat(lessons): judged when written — a new lesson is offered its rules, and "no rule fits" is an answer (milestone 440 step 2, #4631)

"Which rule is this lesson an instance of?" now has three recorded answers:
a rule named (a confirmed link, #4630), no rule fits (new), or unjudged.

- Model + migration 0112: lesson_no_rule (lesson_id PK, CASCADE from the
  note; why; judged_at). A table rather than a key in notes.data, because
  that mirror is re-composed from the body on every edit and would erase it.
- Service (lesson_rules): set_no_rule rejects any confirmed link with the
  reason; a confirmation (set_lesson_rules or judge_link) deletes the answer;
  require_one_answer refuses both answers in one call before any write;
  judgments_for_lessons + attach_lesson_rules add rule_judgment (and no_rule)
  to every lesson payload; list_unjudged lists the open ones; rule_candidates
  searches rules with the lesson's claim + trigger at the explicit-search bar,
  None when the search could not run.
- MCP: create_lesson/update_lesson take no_rule; an unanswered create returns
  rule_candidates, rule_judgment and a rule_hint; list_lessons(unjudged=true).
- REST: the same on POST/PATCH /api/lessons and GET ?unjudged=1; create
  returns rule_candidates.
- Backup v19: a lesson_no_rule section, export (full and per-user) and import.
- Guidance: create_lesson docstring, writing-records.md in using-scribe (owner,
  pinned in test_guidance_ownership), create_rule docstring on linking the
  lessons a new rule governs. Plugin version minted.
- Tests: door units, integration for the three states, the rejection reason,
  scoping, cascade; backup registries.

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

tests/test_services_backup.py

@@ -27,7 +27,7 @@ def test_backup_version_is_current():
 
     (Named for the number it asserted until v10, which is exactly the drift a
     name-carrying-a-value invites; it now says what it checks.)"""
-    assert backup.BACKUP_VERSION == 18
+    assert backup.BACKUP_VERSION == 19
 
 
 def _exportable_note(**over):
@@ -131,7 +131,7 @@ def test_a_repo_binding_carries_the_branch_its_ledger_follows():
 def _column_guard_targets():
     from scribe.models.canonical_system import CanonicalSystem
     from scribe.models.code_shape import CodeShape, CodeShapeEvent, CodeShapeUse
-    from scribe.models.lesson_rule_link import LessonRuleLink
+    from scribe.models.lesson_rule_link import LessonNoRule, LessonRuleLink
     from scribe.models.design_system import DesignSystem, DesignToken
     from scribe.models.milestone import Milestone
     from scribe.models.note import Note
@@ -169,6 +169,7 @@ def _column_guard_targets():
         "note_supersessions": (NoteSupersession, backup._note_supersession_rows),
         "rule_relations": (RuleRelation, backup._rule_relation_rows),
         "lesson_rule_links": (LessonRuleLink, backup._lesson_rule_link_rows),
+        "lesson_no_rule": (LessonNoRule, backup._lesson_no_rule_rows),
         "note_usage_events": (NoteUsageEvent, backup._usage_event_rows),
         "rule_usage_events": (RuleUsageEvent, backup._rule_usage_event_rows),
         "retrieval_tuning_events": (
@@ -286,6 +287,7 @@ def _import_guard_targets():
         "note_supersessions": backup._build_note_supersession,
         "rule_relations": backup._build_rule_relation,
         "lesson_rule_links": backup._build_lesson_rule_link,
+        "lesson_no_rule": backup._build_lesson_no_rule,
         "note_usage_events": backup._build_usage_event,
         "rule_usage_events": backup._build_rule_usage_event,
         "retrieval_tuning_events": backup._build_retrieval_tuning_event,
@@ -539,7 +541,9 @@ async def test_export_full_backup_contains_every_declared_section():
                 # v16: the reasons beside the settings they explain.
                 "retrieval_tuning_events",
                 # v18: which rule each lesson is an instance of.
-                "lesson_rule_links"):
+                "lesson_rule_links",
+                # v19: the lessons judged to fall under no rule.
+                "lesson_no_rule"):
         assert key in out, f"missing export section: {key}"
         assert out[key] == []