refactor(retrieval): the notes arms run on the one pipeline - auto_inject, its reuse and lesson slots, the write path by meaning, and rule_via_lesson are specs (milestone 456 step 4, #4906)

retrieval_pipeline gains the notes half: NoteArm / NoteSlot / NoteMoment /
NoteIO / NoteResult and run_note_arm, which writes once the stages both
notes arms copied: search, withhold this response's own menu (#3739),
fresh/repeat split, the call row before any return (#3497, #3752), the
band, the reserved slots in their order (reuse evicts, lesson extends),
and the surfacing rows. The note renderer (_record_kind, _menu_name,
_menu_passage, the seen pointer, menu_entry) moves with it, and
run_via_lesson_arm takes rule_via_lesson.

Behaviour-preserving, with flags for today's differences: notes still log
BEFORE the band and rules after it (step 7's question). One deliberate
change: a notes arm now fails open like the rule arms, so a failing
search costs its lines and no longer the whole hook response.

The I/O is resolved from plugin_context at call time (_note_io), so the
existing patches keep working. The review re-run reads the AUTO_INJECT
spec instead of restating it, and its guard now compares the two live
searches. The registry declares the pipeline's notes fan-out sites.

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

tests/test_services_plugin_context.py

@@ -3,6 +3,7 @@ from unittest.mock import AsyncMock, MagicMock, patch
 import pytest
 from scribe.services import plugin_context as pc_module
 from scribe.services import retrieval_surfaces as rs
+from scribe.services.retrieval_pipeline import REUSE_SLOT
 from scribe.services.lessons import LESSON_NOTE_TYPE
 from tests.helpers import fake_note, writepath_cfg
 
@@ -340,7 +341,7 @@ _CFG = {"enabled": True, "threshold": 0.55, "top_k": 3}
 def _asked_for_reuse(calls: list[dict]) -> bool:
     """Did the reuse slot issue its reserved query on this run?"""
     return any(
-        tuple(c.get("note_type") or ()) == pc_module._REUSE_KINDS for c in calls
+        tuple(c.get("note_type") or ()) == REUSE_SLOT.kinds for c in calls
     )