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/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"}