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>

src/scribe/mcp/tools/search.py

@@ -596,19 +596,7 @@ It is an UPPER BOUND per surface: a pull records the door it came
       Only ever raised for unbidden arms known to log unconditionally: a
       search returning a list every time is doing its job, and an arm whose
       zeros were never written would flag a LOGGING bug while pointing you at
-      a threshold, which is #3497 exactly. Nor for an arm whose query never
-      changes — see the next entry.
-    - `fixed_query_never_clears` — an arm that always searches the SAME query
-      returned nothing on every call. Its score is one constant, so this is
-      not a quiet window: the bar sits above that constant and no amount of
-      further traffic will produce a different result. The arm is off rather
-      than silent, and nothing else here would say so. The same property is
-      why `cannot_decline` is not raised for these arms: with a constant
-      score the decline rate is 0% or 100% by construction, so "never
-      declined" is arithmetic and not evidence about the floor. Read the
-      refused record (`near_miss_samples`) BEFORE moving the dial — the last
-      time an arm sat here, every percentile said lower it and the refused
-      record showed the refusal was right.
+      a threshold, which is #3497 exactly.
     - `band_hugs_floor` — the weakest tenth of what an arm returns sits on
       its floor. The bar is doing the selecting and the score is not, so
       moving that floor changes how MUCH you get, not how good it is.

src/scribe/mcp/tools/tasks.py

@@ -40,7 +40,6 @@ from scribe.services.notes import minted_kind
 from scribe.services import placement as placement_svc
 from scribe.services import planning as planning_svc
 from scribe.services import record_batch as batch_svc
-from scribe.services import reply_preferences as reply_prefs_svc
 from scribe.services import rulebooks as rulebooks_svc
 from scribe.services import systems as systems_svc
 from scribe.services import task_logs as task_logs_svc
@@ -418,13 +417,11 @@ async def update_task(
 
     Closing a task (done or cancelled) also returns `reply_shape`, the
     default shape of the completion report you are about to write, and
-    `report_back`: a one-line reminder of what that reply should cover. When the
-    operator has preferences for how a completion report is written, they
-    come back as `reply_preferences` ({id, title, statement, kind}) — found
-    by their `when_to_apply`, so a preference whose trigger is writing the
-    report after finishing a task is the one that arrives here. Where one
-    differs from the default shape, the preference is what the operator
-    asked for. When family adoptions were answered `owed` while the task was
+    `report_back`: a one-line reminder of what that reply should cover. The
+    operator's own preferences for that report arrive beside it in
+    `moment_rules` — the ones mounted on finishing work. Where one differs
+    from the default shape, the preference is what the operator asked for.
+    When family adoptions were answered `owed` while the task was
     open, they come back as `family_owed` ({idea_id, idea_title, project_id,
     project_title, owed_task_id}): name each in the report — it is work
     filed into that project.
@@ -470,14 +467,6 @@ async def update_task(
         await family_svc.attach_family_hint(uid, data, note, created=False)
     if status in _CLOSING_STATUSES:
         data["report_back"] = REPORT_BACK_CUE
-        # The operator's own adjustments to the completion report, retrieved
-        # at the one moment a server can see that report coming (milestone
-        # 409 step 4). Omitted rather than sent empty, like every decoration.
-        prefs = await reply_prefs_svc.completion_preferences(
-            uid, project_id=getattr(note, "project_id", None))
-        if prefs:
-            data["reply_preferences"] = prefs
-            data["report_back"] = REPORT_BACK_CUE + " " + REPLY_PREFERENCES_CUE
         # Owed family adoptions filed while the task was open (milestone 463
         # step 6) — work now waiting in some project, which the report names.
         await family_adoption_svc.attach_owed_adoptions(uid, data, note)
@@ -541,12 +530,6 @@ REPORT_BACK_CUE = (
     "Reporting this to the operator? Say where it sits (from `placement`), "
     "what now works, what needs them, and what comes next."
 )
-# Appended only when `reply_preferences` is present, so the key never arrives
-# unexplained and a session with no preferences reads exactly what it did.
-REPLY_PREFERENCES_CUE = (
-    "The operator has preferences for how this report is written — "
-    "follow `reply_preferences` over the default shape where they differ."
-)
 
 _ITEM_KEYS = {"title", "body", "type", "status", "priority", "kind", "tags", "system_ids"}