Remove fallback node scanner

The fallback node scanner introduced with #603 intents to pick up nodes
which our zeroconf scanner missed. There is currently no indication
that the zeroconf scanner misses nodes (anymore), so the fallback
scanner is redundant. This PR removes the fallback scanner.

matter_server/server/device_controller.py

@@ -87,7 +87,6 @@
 NODE_PING_TIMEOUT = 10
 NODE_PING_TIMEOUT_BATTERY_POWERED = 60
 NODE_MDNS_SUBSCRIPTION_RETRY_TIMEOUT = 30 * 60
-FALLBACK_NODE_SCANNER_INTERVAL = 30 * 60
 CUSTOM_ATTRIBUTES_POLLER_INTERVAL = 30
 
 MDNS_TYPE_OPERATIONAL_NODE = "_matter._tcp.local."
@@ -156,8 +155,6 @@ def __init__(
         self._known_commissioning_params_timers: dict[int, asyncio.TimerHandle] = {}
         self._aiobrowser: AsyncServiceBrowser | None = None
         self._aiozc: AsyncZeroconf | None = None
-        self._fallback_node_scanner_timer: asyncio.TimerHandle | None = None
-        self._fallback_node_scanner_task: asyncio.Task | None = None
         self._thread_node_setup_throttle = asyncio.Semaphore(5)
         self._mdns_event_timer: dict[str, asyncio.TimerHandle] = {}
         self._polled_attributes: dict[int, set[str]] = {}
@@ -218,18 +215,12 @@ async def start(self) -> None:
             services,
             handlers=[self._on_mdns_service_state_change],
         )
-        # set-up fallback node scanner
-        self._schedule_fallback_scanner()
 
     async def stop(self) -> None:
         """Handle logic on server stop."""
-        # shutdown (and cleanup) mdns browser and fallback node scanner
+        # shutdown (and cleanup) mdns browser
         if self._aiobrowser:
             await self._aiobrowser.async_cancel()
-        if self._fallback_node_scanner_timer:
-            self._fallback_node_scanner_timer.cancel()
-        if (scan_task := self._fallback_node_scanner_task) and not scan_task.done():
-            scan_task.cancel()
         if self._aiozc:
             await self._aiozc.async_close()
         # Ensure any in-progress setup tasks are cancelled
@@ -1623,43 +1614,6 @@ async def _node_offline(self, node_id: int) -> None:
         # mark node as unavailable (if it wasn't already)
         self._node_unavailable(node_id)
 
-    async def _fallback_node_scanner(self) -> None:
-        """Scan for operational nodes in the background that are missed by mdns."""
-        # This code could/should be removed in the future and is added to have a fallback
-        # to discover operational nodes that got somehow missed by zeroconf.
-        # the issue in zeroconf is being investigated and in the meanwhile we have this fallback.
-        for node_id, node in self._nodes.items():
-            if node.available:
-                continue
-            now = time.time()
-            last_seen = self._node_last_seen_on_mdns.get(node_id, 0)
-            if now - last_seen < FALLBACK_NODE_SCANNER_INTERVAL:
-                continue
-            if await self.ping_node(node_id, attempts=3):
-                LOGGER.info("Node %s discovered using fallback ping", node_id)
-                if task := self._setup_node_create_task(node_id):
-                    await task
-
-        # reschedule self to run at next interval
-        self._schedule_fallback_scanner()
-
-    def _schedule_fallback_scanner(self) -> None:
-        """Schedule running the fallback node scanner at X interval."""
-        if existing := self._fallback_node_scanner_timer:
-            existing.cancel()
-
-        def run_fallback_node_scanner() -> None:
-            self._fallback_node_scanner_timer = None
-            if (existing := self._fallback_node_scanner_task) and not existing.done():
-                existing.cancel()
-            self._fallback_node_scanner_task = asyncio.create_task(
-                self._fallback_node_scanner()
-            )
-
-        self._fallback_node_scanner_timer = self._loop.call_later(
-            FALLBACK_NODE_SCANNER_INTERVAL, run_fallback_node_scanner
-        )
-
     async def _custom_attributes_poller(self) -> None:
         """Poll custom clusters/attributes for changes."""
         for node_id in tuple(self._polled_attributes):