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/routes/plugin.py

@@ -294,6 +294,42 @@ async def moment():
     })
 
 
+@plugin_bp.post("/reply-rules")
+@login_required
+@memoized_query_embeddings
+async def reply_rules():
+    """Whether the reply that ends a turn is held for one read (milestone 458).
+
+    Called by the plugin's Stop hook with the finished reply. Two halves: the
+    rules MOUNTED on the reply moments (`reply.report`, and `reply.ask` when
+    the reply asks something), and the reply text against every rule's
+    trigger — the backstop for whatever the earlier arms missed.
+
+    Body: `{"reply": "<text>"}`. Query: `repo` / `project_id` for the scope;
+    `held_rule_ids` (opened this session — exempt, as at the act checkpoint);
+    `exclude_rule_ids` (named this session — not re-counted as surfaced);
+    `stopped_rule_ids` (already held a reply or an act this session — a rule
+    holds once, and the per-session cap counts these).
+
+    Returns `reason` — the words the hook blocks with, empty when nothing
+    holds — plus `rule_ids` for the hook's ledger and `moments` reached.
+    """
+    data = await request.get_json(silent=True) or {}
+    reply = str(data.get("reply") or "")
+    project_id, _repo, _unbound = await _project_scope()
+    held = await moment_delivery_svc.reply_hold(
+        g.user.id, reply, project_id=project_id,
+        exclude=frozenset(_int_list(request.args.get("exclude_rule_ids"))),
+        held=frozenset(_int_list(request.args.get("held_rule_ids"))),
+        stopped=frozenset(_int_list(request.args.get("stopped_rule_ids"))),
+    )
+    return jsonify({
+        "reason": held.get("reason", ""),
+        "rule_ids": held.get("rule_ids", []),
+        "moments": held.get("moments", []),
+    })
+
+
 @plugin_bp.get("/prior-art")
 @login_required
 @memoized_query_embeddings