Heartbeat per event class, not per source

audit-core's completeness contract landed, and our single per-source beat
is the shape it rules inadequate: it is discharged by whichever class is
busy, so a revocation stream that has gone silent looks identical to a
quiet one — and revocation is the only silence here that matters.

Emit one nothing-to-report assertion per declared class, all four in one
transaction so a partial emission cannot report some classes healthy and
others stalled. Carry type audit-core.heartbeat with class and assertion
on data. Pin that the first beat goes out at startup rather than an
interval later, since a declared-but-never-sent class is their
no_heartbeat_since_registration finding and not a skip.

Declare heartbeat_classes and the reconciliation surface in the source
registration, including the residual neither control covers: a
compromised emitter suppresses the event and its own heartbeat together.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HyybaE7DUXrWYrhbnESCTe

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1275879@bnt-lap001
Assistant-Session: eb464208-f821-41b2-bc5a-a6c33d92a8ad

approval_engine/audit.py

@@ -18,6 +18,13 @@ class AuditDeliveryError(RuntimeError):
 
 def audit_envelope(payload: dict[str, Any]) -> dict[str, Any]:
     details = dict(payload.get("details") or {})
+    # audit-core's heartbeat contract puts the asserted class and the assertion
+    # on `data` itself, not inside a producer-shaped details object.
+    heartbeat = (
+        {"class": details.get("class"), "assertion": details.get("assertion")}
+        if payload["action"] == "audit-core.heartbeat"
+        else {}
+    )
     return {
         "id": payload["event_id"],
         "type": payload["action"],
@@ -34,6 +41,7 @@ def audit_envelope(payload: dict[str, Any]) -> dict[str, Any]:
             "outcome": payload["outcome"],
             "reason": payload.get("reason"),
             "details": details,
+            **heartbeat,
         },
     }