feat(4636): rule pull-through per surface, and per-rule usage with confirmed lessons on list_rules

retrieval_telemetry gains rule_usage.by_source, the twin of usage.by_source:
distinct rules each surface showed, how many an agent opened, and a ratio
that is null on a bulk delivery. list_rules(with_usage=True, days=N) adds
each rule's usage, windowed, and how many lessons are confirmed instances
of it, so linked and unlinked rules can be compared through MCP.

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

tests/test_mcp_tool_rulebooks.py

@@ -573,3 +573,36 @@ def test_rule_outcome_is_registered_and_is_not_read_only():
     assert "rule_outcome" in mcp.names
     assert "rule_outcome" in _WRITE_TOOLS
     assert "rule_outcome" not in _READ_ONLY_TOOLS
+
+
+@pytest.mark.asyncio
+async def test_list_rules_carries_usage_only_when_asked():
+    """A listing is for applying rules, so it stays lean; `with_usage` adds
+    each rule's telemetry and confirmed-lesson count for judging them, with
+    `days` passed down as a window."""
+    from grimoire.mcp.tools import rulebooks as tools
+    from grimoire.services.rule_usage import empty_rule_usage
+
+    rows = [fake_rule(id=1, title="dev is home"), fake_rule(id=2, title="ask first")]
+    seen = {**empty_rule_usage(), "surfaced_count": 4, "pull_count": 1}
+    usage = AsyncMock(return_value={1: seen})
+    lessons = AsyncMock(return_value={1: 3})
+    with patch.object(tools.rulebooks_svc, "list_rules", AsyncMock(return_value=rows)), \
+         patch.object(tools.rulebooks_svc, "list_rule_moments", AsyncMock(return_value={})), \
+         patch.object(tools, "usage_for_rules", usage), \
+         patch.object(tools, "confirmed_lesson_counts", lessons):
+        lean = await tools.list_rules()
+        assert all("usage" not in r and "confirmed_lessons" not in r for r in lean["rules"])
+        usage.assert_not_awaited()
+
+        out = await tools.list_rules(with_usage=True, days=14)
+
+    by_id = {r["id"]: r for r in out["rules"]}
+    assert by_id[1]["usage"]["surfaced_count"] == 4
+    assert by_id[1]["confirmed_lessons"] == 3
+    # A rule missing from either read is zero-filled, never absent.
+    assert by_id[2]["usage"] == empty_rule_usage()
+    assert by_id[2]["confirmed_lessons"] == 0
+    assert usage.await_args.args[0] == [1, 2]
+    assert usage.await_args.kwargs["since"] is not None
+    lessons.assert_awaited_once_with(7, [1, 2])