feat(moments): rules mount on moments, through every rule door (milestone 458 step 3, #4921)

rule_moments (migration 0117) records which moments a rule arrives at, by
catalog name, cascading with the rule. rule_detail, the one seam every
rule door already returns through, gains moments beside system_ids: None
leaves the mounts alone, a list replaces them. get_rule and both
list_rules doors read them back, batched per page.

All five MCP rule/preference writes and the three REST ones take moments
and validate them before their create or update. An unknown name is
refused with the catalog listed and leaves no half-made rule behind; a
parity test pins that ordering on every door.

Backup v22 carries the mounts as a join table remapped through the rule
map; a real-Postgres round trip checks they land on the restored rule.

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

src/scribe/routes/rulebooks.py

@@ -8,6 +8,7 @@ from __future__ import annotations
 from quart import Blueprint, jsonify, request
 
 from scribe.auth import get_current_user_id, login_required
+import scribe.services.moments as moments_svc
 import scribe.services.rulebooks as rulebooks_svc
 from scribe.services.trash import delete as trash_delete
 from scribe.services.rule_usage import (
@@ -17,6 +18,15 @@ from scribe.services.rule_usage import (
 rulebooks_bp = Blueprint("rulebooks", __name__, url_prefix="/api")
 
 
+def _moments_or_refusal(data: dict):
+    """The request's `moments`, validated BEFORE any write — so an unknown
+    name is a 400 and not a rule created without the mounts it asked for.
+    Absent means "leave them alone" (None), as on the MCP door."""
+    try:
+        return moments_svc.require_moments(data.get("moments")), None
+    except ValueError as exc:
+        return None, (jsonify({"error": str(exc)}), 400)
+
 
 # ── Rulebooks ───────────────────────────────────────────────────────────
 
@@ -154,8 +164,12 @@ async def list_rules():
     # than for snippets: every rule on every install predates this table, so
     # for a while the zero-filled shape IS the common case.
     usage = await usage_for_rules([int(it["id"]) for it in items])
+    # Zero-filled like `usage`, for the same reason: the UI renders "mounted
+    # nowhere" from an empty list rather than treating a missing key as a state.
+    mounted = await rulebooks_svc.list_rule_moments([int(it["id"]) for it in items])
     for it in items:
         it["usage"] = usage.get(int(it["id"]), empty_rule_usage())
+        it["moments"] = mounted.get(int(it["id"]), [])
     return jsonify({"rules": items})
 
 
@@ -167,6 +181,9 @@ async def create_rule(topic_id: int):
     statement = (data.get("statement") or "").strip()
     if not title or not statement:
         return jsonify({"error": "title and statement are required"}), 400
+    moments, refused = _moments_or_refusal(data)
+    if refused:
+        return refused
     try:
         rule = await rulebooks_svc.create_rule(
             topic_id=topic_id,
@@ -189,7 +206,7 @@ async def create_rule(topic_id: int):
     except ValueError as exc:
         return jsonify({"error": str(exc)}), 404
     return jsonify(await rulebooks_svc.rule_detail(
-        get_current_user_id(), rule, data.get("system_ids"),
+        get_current_user_id(), rule, data.get("system_ids"), moments,
     )), 201
 
 
@@ -223,10 +240,15 @@ async def update_rule(rule_id: int):
     # service normalises "" to NULL for every nullable text column. The MCP
     # door needs the explicit list only because "" already means "unchanged"
     # there — two idioms, one outcome.
+    moments, refused = _moments_or_refusal(data)
+    if refused:
+        return refused
     rule = await rulebooks_svc.update_rule(rule_id, uid, **fields)
     if rule is None:
         return jsonify({"error": "rule not found"}), 404
-    return jsonify(await rulebooks_svc.rule_detail(uid, rule, data.get("system_ids")))
+    return jsonify(await rulebooks_svc.rule_detail(
+        uid, rule, data.get("system_ids"), moments,
+    ))
 
 
 @rulebooks_bp.get("/rules/<int:rule_id>/versions")
@@ -401,6 +423,9 @@ async def create_project_rule(project_id: int):
                      "surfaces at the moment it applies."
         }), 400
     title = (data.get("title") or "").strip() or statement.split(".")[0][:50]
+    moments, refused = _moments_or_refusal(data)
+    if refused:
+        return refused
     try:
         rule = await rulebooks_svc.create_project_rule(
             project_id=project_id,
@@ -423,7 +448,7 @@ async def create_project_rule(project_id: int):
     except ValueError as exc:
         return jsonify({"error": str(exc)}), 404
     return jsonify(await rulebooks_svc.rule_detail(
-        get_current_user_id(), rule, data.get("system_ids"),
+        get_current_user_id(), rule, data.get("system_ids"), moments,
     )), 201