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/services/moments.py

@@ -142,6 +142,20 @@ def require_moment(name: str) -> str:
     )
 
 
+def require_moments(names: list[str] | None) -> list[str] | None:
+    """A rule's moments, normalised and de-duplicated — or the first refusal.
+
+    None passes through as None, which every rule door reads as "leave the
+    mounts alone"; a list, [] included, is the whole set after the write.
+    All are checked before any is stored, so a refusal leaves nothing
+    half-mounted.
+    """
+    if names is None:
+        return None
+    if isinstance(names, str):
+        names = [names]
+    return list(dict.fromkeys(require_moment(n) for n in names))
+
 def catalog() -> dict:
     """The catalog as plain data, for the MCP tool and the REST door alike."""
     return {