feat(moments): the reply moment holds a finished reply for one read (milestone 458 step 4b, #4922)

The reply is the one act no tool call marks, and it is where "let me
know if it works" gets said. A new Stop hook (scribe_reply_check.sh)
sends the finished reply to POST /api/plugin/reply-rules, which checks
it twice:

- mounted: every unopened RULE on reply.report, plus reply.ask when the
  reply asks a question. Deterministic.
- semantic: the reply's head and tail against every rule's trigger, on a
  new ranked surface, reply_rule. It is the backstop for whatever the
  earlier arms missed. Its floor is its stop bar (default 0.80, budget
  1), with its own Settings dials. The new stop_only stage records
  surfacing for the rule that holds and nothing else, because nothing
  else reached anyone.

Following the operator's ruling from 456 step 8, a rule that holds blocks
once, in the server's words. The hook blocks only on a reason it was
given, so an unreachable instance never stops a session, and it never
holds the rewrite. The ledger is the act checkpoint's own, so a rule
holds a session once across both doors and the per-session cap counts
both.

The turn reader moved from the report check into scribe_defs.sh
(scribe_turn_facts / scribe_turn_fact), so the two Stop hooks read a
turn the same way. The output was checked identical on a real transcript.

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

src/scribe/services/retrieval_registry.py

@@ -135,6 +135,9 @@ POINTS: dict[str, Point] = dict([
     _p("write_path_rule", UNBIDDEN, "rules that may govern the file being written"),
     _p("pre_tool_rule", UNBIDDEN, "rules that may govern a command about to run"),
     _p("prompt_rule", UNBIDDEN, "rules that may govern what the operator just asked"),
+    _p("reply_rule", UNBIDDEN,
+       "a rule that holds the finished reply for one read — the backstop "
+       "for whatever the earlier arms missed"),
     _p("preference_slot", UNBIDDEN,
        "the one line reserved for a preference at the prompt boundary"),
     _p("reuse_slot", UNBIDDEN, "the one line reserved for a reusable snippet"),