refactor(retrieval): the completion-report preferences run through the pipeline (milestone 456 step 3, #4905)

reply_preferences.completion_preferences was the last hand-written
rule search + record_retrieval + record_rule_surfaced triple outside the
pipeline. It is now REPORT_PREFERENCE, a RuleArm with kind="preference"
over COMPLETION_QUERY, read back as records rather than as lines.

- RuleArm gains `kind`. _ranked asks the ranker for that kind and drops
  anything else on the way out, before the row is logged.
- RuleResult gains `shown`, the (score, rule) pairs behind the lines, for
  callers that return records.
- RuleMoment.project_id may be None: logged as given, searched as
  `project_id or None`. report_preference rows keep their NULL project.
- Guards: reply_preferences now has 0 direct rule searches. The registry
  constant-source example moves from report_preference to preference_slot,
  the pipeline slot that records through a module constant.

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

src/scribe/services/reply_preferences.py

@@ -58,8 +58,8 @@ bar can be wrong forever without a single call looking unusual.
 from __future__ import annotations
 
 import logging
-import time
 
+from scribe.services import retrieval_pipeline as rp
 from scribe.services.embeddings import semantic_search_rules
 from scribe.services.retrieval_surfaces import SURFACES, budget_for, floor_for
 from scribe.services.retrieval_telemetry import record_retrieval
@@ -67,7 +67,7 @@ from scribe.services.rule_usage import record_rule_surfaced
 
 logger = logging.getLogger(__name__)
 
-SOURCE = "report_preference"
+SOURCE = rp.REPORT_PREFERENCE.source
 
 # Written in the vocabulary of the MOMENT, because that is what a trigger is
 # written in and what this query is scored against. Domain-neutral on purpose
@@ -114,34 +114,27 @@ async def completion_preferences(user_id: int, *, project_id: int | None = None)
     happened, and a lookup that errors must not turn it into a failure.
     """
     try:
-        threshold = await _threshold(user_id)
-        limit = await _limit(user_id)
-        report: dict = {}
-        t0 = time.perf_counter()
-        hits = await semantic_search_rules(
-            user_id, COMPLETION_QUERY, limit=limit, threshold=threshold,
-            kind="preference", report=report, project_id=project_id,
-        )
-        hits = [(score, rule) for score, rule in hits if rule.kind == "preference"]
-        record_retrieval(
-            user_id=user_id, source=SOURCE, query=COMPLETION_QUERY,
-            threshold=threshold, limit=limit, project_id=project_id,
-            is_task=None, results=hits,
-            best_available=report.get("best_available_score"),
-            best_available_id=report.get("best_available_id"),
-            searched=bool(report.get("searched", True)),
-            duration_ms=(time.perf_counter() - t0) * 1000.0,
-        )
-        if not hits:
-            return []
+        # The stages — the kind filter, the unconditional call row, the
+        # fresh-only surfacing rows — are the one pipeline's (milestone 456).
         # RANKED: this surface chose what it showed, so the name is in
         # rule_usage.RANKED_SOURCES and its hits count toward pull-through.
-        record_rule_surfaced(
-            user_id=user_id, rule_ids=[rule.id for _s, rule in hits], source=SOURCE,
+        # There is no session ledger here: a completion report is written
+        # once, so nothing it could repeat has been shown before.
+        result = await rp.run_rule_arm(
+            rp.REPORT_PREFERENCE,
+            rp.RuleMoment(
+                user_id=user_id, query=COMPLETION_QUERY, project_id=project_id,
+            ),
+            floor=await _threshold(user_id), budget=await _limit(user_id),
+            io=rp.RuleIO(
+                search=semantic_search_rules,
+                record_retrieval=record_retrieval,
+                record_rule_surfaced=record_rule_surfaced,
+            ),
         )
         return [
             {"id": rule.id, "title": rule.title, "statement": rule.statement, "kind": "preference"}
-            for _score, rule in hits
+            for _score, rule in result.shown
         ]
     except Exception:  # noqa: BLE001 - a decoration never breaks its payload
         logger.warning("completion preference lookup failed", exc_info=True)