feat(500): retire the fixed-question preference arm - completion-report preferences ride the moments

report_preference searched one constant string when a task closed and handed
matches back as update_task's reply_preferences. Milestone 500 step 3 delivers
the reply shapes and the preferences mounted beside them on the moments, so
the arm goes, whole (rule 22):

- services/reply_preferences.py, the REPORT_PREFERENCE RuleArm, its re-scorer
  and corpus entries, and the REPORTPREF constants
- update_task's reply_preferences block and its cue; the docstring now points
  at moment_rules
- the fixed_query field and the fixed_query_never_clears warning: this arm was
  the only one that set it, so the concept and the cannot_decline exemption
  go with it
- the two Settings fields for its floor and budget
- migration 0121 deletes its rows (logs, judgments, rule-usage events, tuning
  history, settings keys), operator-approved 2026-10-09. Without it the
  readout would call the source unregistered and its surfacings would count
  as ambient. The unindexed rule_usage delete is bounded by created_at.

#5496 (step 4 of milestone 500).

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

tests/test_retrieval_surfaces.py

@@ -24,9 +24,9 @@ WHAT THIS PINS
      different file. Renaming one without the other produces a surface that can
      be tuned and cannot be measured, or measured and not tuned, and both fail
      silently.
-  2. **Keys are unique.** Two surfaces sharing a settings key is how
-     `report_preference` spent its first release moving whenever the prompt arm
-     was tuned (#3860) — one dial wearing two labels.
+  2. **Keys are unique.** Two surfaces sharing a settings key is how the
+     completion-report arm (since retired) spent its first release moving
+     whenever the prompt arm was tuned (#3860) — one dial wearing two labels.
   3. **An unknown surface is refused.** Settings keys are free-form strings in
      a generic table, so a typo'd name would write a key nothing reads: a
      change that appears to succeed, reports a new value, and alters nothing.
@@ -44,7 +44,7 @@ import pytest
 
 from scribe.services import retrieval_surfaces as rs
 
-SERVICES = ("plugin_context", "reply_preferences")
+SERVICES = ("plugin_context",)
 
 
 def _service_source(name: str) -> str:
@@ -63,10 +63,6 @@ def test_every_surface_name_is_a_real_telemetry_source():
     to justify a change describes a different arm from the one the change hits.
     """
     blob = "\n".join(_service_source(n) for n in SERVICES)
-    # `report_preference` passes its name through a module constant rather than
-    # a literal, so that one name is satisfied by the constant holding it.
-    from scribe.services.reply_preferences import SOURCE
-
     # The rule arms record through the one pipeline (milestone 456), where
     # `source` is the spec's own field — so for them the spec IS the string
     # `record_retrieval` receives, and the join key is checked against it.
@@ -76,7 +72,7 @@ def test_every_surface_name_is_a_real_telemetry_source():
     missing = [
         s.name for s in rs.SURFACES.values()
         if f'source="{s.name}"' not in blob
-        and s.name != SOURCE and s.name not in via_pipeline
+        and s.name not in via_pipeline
     ]
     assert not missing, (
         f"these surfaces can be tuned but never measured: {missing}. The "