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>

scripts/check_plugin.py

@@ -366,6 +366,12 @@ SMOKE_EVENTS: dict[str, str] = {
         {"session_id": "smoke", "transcript_path": "/nonexistent/smoke.jsonl",
          "cwd": ".", "hook_event_name": "Stop", "stop_hook_active": False}
     ),
+    # The reply moment (milestone 458). No transcript, so no reply: silent and
+    # never a block, configured or not.
+    "scribe_reply_check.sh": json.dumps(
+        {"session_id": "smoke", "transcript_path": "/nonexistent/smoke.jsonl",
+         "cwd": ".", "hook_event_name": "Stop", "stop_hook_active": False}
+    ),
     # The end-of-turn shape check (milestone 439). With no ledger for the
     # session there is nothing to ask about, and with no instance there is
     # nobody to ask: silent, and never a block, configured or not.