Derive heartbeat cadence from the shared coordination frame

Assistant: codex
Assistant-Model: gpt-6-astra
Assistant-Session: 01a13eab-1e6a-7b33-9c37-372e90ada3a2

approval_engine/audit.py

@@ -9,6 +9,7 @@ from typing import Any, Callable
 from urllib.error import HTTPError, URLError
 from urllib.request import Request, urlopen
 
+from .coordination import FRAME_SECONDS
 from .store import Engine
 
 
@@ -91,7 +92,7 @@ class OutboxWorker:
         engine: Engine,
         sink: Callable[[dict[str, Any]], None],
         *,
-        heartbeat_interval_seconds: int = 300,
+        heartbeat_interval_seconds: int = FRAME_SECONDS,
     ) -> None:
         self.engine = engine
         self.sink = sink