🚧 Add broker status page

backend/app/dynsec.py

@@ -61,6 +61,9 @@ class DynsecClient:
         self._lock = threading.Lock()
         self._responses: dict[str, queue.Queue[dict[str, Any]]] = {}
         self._connected = threading.Event()
+        # Optional tap for $SYS telemetry (app.metrics registers itself
+        # at startup). Receives (topic, payload) for every $SYS message.
+        self._event_sink = None
 
     # -- connection lifecycle ------------------------------------------------
     def connect(self) -> None:
@@ -118,12 +121,25 @@ class DynsecClient:
                 return
             self._teardown_locked()
 
+    def set_event_sink(self, sink) -> None:
+        """Register a callable receiving every $SYS message (topic, payload).
+
+        Used by app.metrics for the broker dashboard (spec sections 33,
+        55). The sink must never raise: telemetry must not be able to
+        disturb the management channel.
+        """
+        self._event_sink = sink
+
     # -- paho callbacks -------------------------------------------------------
     def _on_connect(self, client, userdata, flags, reason_code, properties) -> None:
         if reason_code == 0:
             # FIXED response topic — all commands reply here; requests are
             # matched by the correlationData echo inside the payload.
             client.subscribe(RESPONSE_TOPIC, qos=1)
+            # $SYS telemetry for the dashboard (spec sections 33, 55).
+            # qos 0: telemetry is periodically republished, losing one
+            # is harmless.
+            client.subscribe("$SYS/#", qos=0)
             self._connected.set()
         else:
             logger.error("dynsec client connect failed: %s", reason_code)
@@ -149,6 +165,14 @@ class DynsecClient:
 
     def _on_message(self, client, userdata, msg) -> None:
         if msg.topic != RESPONSE_TOPIC:
+            # Not a dynsec reply: forward $SYS telemetry to the sink, if
+            # one is registered. Swallow sink errors — telemetry must
+            # never disturb the management channel.
+            if msg.topic.startswith("$SYS/") and self._event_sink is not None:
+                try:
+                    self._event_sink(msg.topic, msg.payload)
+                except Exception:  # noqa: BLE001
+                    logger.warning("$SYS event sink raised; message dropped")
             return
         try:
             payload = json.loads(msg.payload.decode("utf-8"))