feat(rules): a rule surfaces through the lessons confirmed as its instances (milestone 440 step 4, #4633)

On all three rule arms (prompt_rule, pre_tool_rule, write_path_rule), after
the direct match, a lesson matching the moment at the notes menu's own bar
brings the rule(s) it is CONFIRMED to be an instance of, rendered in rule
voice with "Reached through lesson #N “…”, a recorded instance of it."

- Confirmed links only (lesson_rules.confirmed_lessons /
  confirmed_rules_in_scope). A suggested link carrying its rule would
  manufacture the co-arrival #4637 counts and prove itself.
- Scope kept: a lesson surfaces everywhere, but the rule it brings must be
  global or this project's own — milestone 414's boundary, not reopened
  through a side door.
- Suppression is by RULE: anything the direct band named or the session
  ledger holds is skipped, whichever lesson reached it.
- Its own slot (VIA_LESSON_LIMIT = 1), not a rule slot — a stated default,
  since the plan's "decide by measurement" has nothing to measure until
  links are confirmed (#4632). Its own source, rule_via_lesson: registered,
  RANKED for pull-through, logged whenever it searches.
- Nothing searched at all while no lesson carries a confirmed link, which is
  every install until one is judged.
- build_prompt_rule_hint / build_tool_rule_hint are now thin wrappers over
  the direct arms (_prompt_rule_hint / _tool_rule_hint); the arm leaves its
  query in `_via_query` only when it ran, so a disabled arm or a blank prompt
  brings no rule in either, and the key never leaves the server.
- Via-lesson rules are not fed to the #4637 co-surfacing recorder: only
  direct matches are evidence.

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

tests/test_integration_lesson_rule_links.py

@@ -314,3 +314,36 @@ async def test_confirming_a_suggestion_keeps_what_it_rested_on(world):
     out = await links_svc.judge_link(world["owner"], world["lesson"], world["r1"], "confirm", "same failure class")
     assert out["state"] == "confirmed"
     assert len(out["evidence"]["situations"]) == 3
+
+
+# ── #4633: which links can carry a rule ─────────────────────────────────────
+
+
+async def test_only_a_confirmed_link_can_carry_its_rule(world):
+    """A suggested link never expands: it would manufacture the co-arrival
+    that #4637 counts, and prove itself. A rejected one obviously not."""
+    owner, lesson = world["owner"], world["lesson"]
+    await links_svc.co_surfaced(owner, [lesson], [world["r1"]], arm="p", situation="one ask here")
+    await links_svc.judge_link(owner, lesson, world["r2"], "reject", "not this")
+    assert await links_svc.confirmed_lessons(owner) == set()
+    assert await links_svc.confirmed_rules_in_scope(owner, [lesson], world["mine"]) == {}
+
+    await links_svc.judge_link(owner, lesson, world["r1"], "confirm", "same failure class")
+    assert lesson in await links_svc.confirmed_lessons(owner)
+    rules = await links_svc.confirmed_rules_in_scope(owner, [lesson], world["mine"])
+    assert [r.id for r in rules[lesson]] == [world["r1"]]
+
+
+async def test_a_project_rule_stays_in_its_project_even_through_a_lesson(world):
+    """Milestone 414's scope, kept on the side door: the lesson surfaces
+    everywhere, its project rule only in its project."""
+    owner, lesson = world["owner"], world["lesson"]
+    await links_svc.set_lesson_rules(owner, lesson, [world["r1"]])
+    assert await links_svc.confirmed_rules_in_scope(owner, [lesson], world["mine"])
+    assert await links_svc.confirmed_rules_in_scope(owner, [lesson], world["theirs"]) == {}
+    assert await links_svc.confirmed_rules_in_scope(owner, [lesson], None) == {}
+
+
+async def test_a_stranger_reaches_no_rule_through_someone_elses_link(world):
+    await links_svc.set_lesson_rules(world["owner"], world["lesson"], [world["r1"]])
+    assert await links_svc.confirmed_lessons(world["stranger"]) == set()