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_rule_via_lesson.py

@@ -0,0 +1,147 @@
+"""A rule reached through its lessons (milestone 440, #4633).
+
+The step runs after each of the three rule arms. These pin, with the database
+and the embedder stubbed: that nothing is searched when no lesson carries a
+confirmed link; that a matching linked lesson brings its rule in rule voice,
+naming the lesson; that suppression is by RULE; that the slot holds one line;
+and that the call is logged under its own source. That a SUGGESTED link never
+expands — the soft link proving itself — is pinned against Postgres in
+tests/test_integration_lesson_rule_links.py, where the state filter lives.
+"""
+from __future__ import annotations
+
+from types import SimpleNamespace
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from scribe.services import plugin_context as pc
+from scribe.services import rule_usage
+from scribe.services.retrieval_registry import POINTS
+
+# Bound before conftest's autouse stub replaces the module attribute.
+_REAL = pc._rules_via_lessons
+
+
+def _lesson(lid=41, title="An overrun run usually failed early"):
+    return SimpleNamespace(
+        id=lid, title=title, note_type="lesson", body="",
+        data={"what": title, "when_to_apply": "a CI run overran"},
+    )
+
+
+def _rule(rid, title="Read the job log first", kind="rule"):
+    return SimpleNamespace(id=rid, title=title, kind=kind, when_to_apply="a run overran")
+
+
+def _stubs(*, confirmed, found, by_lesson):
+    log, surfaced = MagicMock(), MagicMock()
+    stack = [
+        patch.object(pc.lesson_rules_svc, "confirmed_lessons", AsyncMock(return_value=confirmed)),
+        patch.object(pc.lesson_rules_svc, "confirmed_rules_in_scope", AsyncMock(return_value=by_lesson)),
+        patch.object(pc, "get_autoinject_config", AsyncMock(return_value={"threshold": 0.5})),
+        patch.object(pc, "semantic_search_notes", AsyncMock(return_value=found)),
+        patch.object(pc, "record_retrieval", log),
+        patch.object(pc, "record_rule_surfaced", surfaced),
+    ]
+    return stack, log, surfaced
+
+
+async def _run(stack, **kw):
+    for p in stack:
+        p.start()
+    try:
+        return await _REAL(1, "the CI run is still going", project_id=2,
+                           skip=kw.get("skip", set()), held=set(), where="to this request")
+    finally:
+        for p in stack:
+            p.stop()
+
+
+@pytest.mark.asyncio
+async def test_no_confirmed_link_means_no_search_and_no_row():
+    search = AsyncMock()
+    stack, log, _ = _stubs(confirmed=set(), found=[], by_lesson={})
+    stack[3] = patch.object(pc, "semantic_search_notes", search)
+    assert await _run(stack) == ([], [])
+    search.assert_not_awaited()
+    log.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_a_matching_linked_lesson_brings_its_rule_in_rule_voice():
+    stack, log, surfaced = _stubs(
+        confirmed={41}, found=[(0.71, _lesson())], by_lesson={41: [_rule(7)]},
+    )
+    lines, ids = await _run(stack)
+    assert ids == [7]
+    assert lines[0].startswith("Standing rule")
+    assert "Reached through lesson #41" in lines[0]
+    assert log.call_args.kwargs["source"] == "rule_via_lesson"
+    assert surfaced.call_args.kwargs == {"user_id": 1, "rule_ids": [7], "source": "rule_via_lesson"}
+
+
+@pytest.mark.asyncio
+async def test_a_lesson_without_a_confirmed_link_carries_nothing():
+    """The search found a lesson, but it is not in the confirmed set — a
+    suggested or unlinked lesson brings no rule."""
+    stack, log, surfaced = _stubs(
+        confirmed={99}, found=[(0.9, _lesson(41))], by_lesson={},
+    )
+    assert await _run(stack) == ([], [])
+    surfaced.assert_not_called()
+    assert log.call_args.kwargs["results"] == []
+
+
+@pytest.mark.asyncio
+async def test_suppression_is_by_rule_whichever_lesson_reached_it():
+    stack, log, surfaced = _stubs(
+        confirmed={41}, found=[(0.71, _lesson())], by_lesson={41: [_rule(7)]},
+    )
+    assert await _run(stack, skip={7}) == ([], [])
+    assert log.call_args.kwargs["suppressed"] == 1
+    surfaced.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_the_slot_holds_one_line():
+    stack, _log, _ = _stubs(
+        confirmed={41, 42},
+        found=[(0.8, _lesson(41)), (0.7, _lesson(42, "Another"))],
+        by_lesson={41: [_rule(7), _rule(8)], 42: [_rule(9)]},
+    )
+    lines, ids = await _run(stack)
+    assert ids == [7] and len(lines) == pc.VIA_LESSON_LIMIT == 1
+
+
+@pytest.mark.asyncio
+async def test_a_failure_brings_no_rule_and_raises_nothing():
+    stack, _log, _ = _stubs(confirmed={41}, found=[], by_lesson={})
+    stack[0] = patch.object(pc.lesson_rules_svc, "confirmed_lessons",
+                            AsyncMock(side_effect=RuntimeError("db down")))
+    assert await _run(stack) == ([], [])
+
+
+@pytest.mark.asyncio
+async def test_the_step_runs_only_when_the_arm_ran_and_never_leaks_its_key():
+    step = AsyncMock(return_value=(["Standing rule … Reached through lesson #41"], [7]))
+    with patch.object(pc, "_rules_via_lessons", step):
+        idle = await pc._add_rules_via_lessons(
+            1, {"context": "", "rule_ids": []}, project_id=2,
+            exclude_rule_ids=[3], held_rule_ids=[], where="here",
+        )
+        ran = await pc._add_rules_via_lessons(
+            1, {"context": "direct line", "rule_ids": [5], "_via_query": "q"},
+            project_id=2, exclude_rule_ids=[3], held_rule_ids=[], where="here",
+        )
+    assert idle == {"context": "", "rule_ids": []}
+    assert step.await_count == 1
+    assert step.await_args.kwargs["skip"] == {3, 5}
+    assert "_via_query" not in ran
+    assert ran["rule_ids"] == [5, 7]
+    assert ran["context"].startswith("direct line\n")
+
+
+def test_the_source_is_ranked_and_registered():
+    assert "rule_via_lesson" in rule_usage.RANKED_SOURCES
+    assert "rule_via_lesson" in POINTS