Carry transport local-name events on a throws-configured bus

The zeroconf transport's .local hostname events moved onto a new bus during
the KolibriBroadcast split, but it was instantiated as a plain
magicbus.base.Bus, which has no throws attribute. Bus.publish references
self.throws in its listener error path, so any exception raised by a
local-name listener (LocalHostnameListener -> sync_local_hostnames.enqueue)
surfaced as a masking AttributeError instead of propagating.

Restore the original KolibriBroadcastEvents behaviour with a LocalNameEvents
bus subclass that sets throws = (Exception,), mirroring NetworkDiscoveryEvents.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: rtibblesbot

kolibri/core/discovery/test/test_network_broadcast.py

@@ -408,6 +408,16 @@ def test_update_returns_true_and_rebinds_when_addresses_changed(self, mock_renew
             interfaces=self.transport.interfaces
         )
 
+    def test_local_name_event_listener_error_propagates(self):
+        # A raising local-name listener must surface its own exception, not an
+        # AttributeError from a bus with no `throws` configured.
+        def boom(hostnames):
+            raise ValueError("boom")
+
+        self.transport.events.subscribe(EVENT_UPDATE_LOCAL_NAMES, boom)
+        with self.assertRaises(ValueError):
+            self.transport.events.publish(EVENT_UPDATE_LOCAL_NAMES, [])
+
     @mock.patch(BROADCAST_MODULE + "ServiceBrowser")
     def test_start_listening_attaches_browser(self, mock_browser):
         self.transport.zeroconf = self.zeroconf

kolibri/core/discovery/utils/network/broadcast.py

@@ -521,6 +521,21 @@ def on_remove(self, name):
             self.events.publish(EVENT_REMOVE_INSTANCE, instance)
 
 
+class LocalNameEvents(Bus):
+    """
+    Event bus carrying only the transport's `.local` hostname events. Kept
+    separate from the backend's instance bus so local-name concerns stay inside
+    the transport.
+    """
+
+    # Provides better stack traces for errors when you list potential exception types here.
+    # Adding `Exception` here will re-raise all errors, but making it easier to debug.
+    throws = (Exception,)
+
+    def __init__(self):
+        super().__init__(extra_channels=[EVENT_UPDATE_LOCAL_NAMES])
+
+
 class ZeroconfNetworkDiscovery:
     """
     The default zeroconf transport for network discovery. Implements the
@@ -541,7 +556,7 @@ def __init__(self):
         self.instance = None
         self.local_names = {}
         # our own bus, carrying only the `.local` hostname events
-        self.events = Bus(extra_channels=[EVENT_UPDATE_LOCAL_NAMES])
+        self.events = LocalNameEvents()
         # backend callbacks, stored on start_listening
         self._on_add = None
         self._on_update = None