fix: move cancel_event signal outside lock for immediate delivery

The cancel_event.set() call was inside the async lock context in
_on_config_change, causing delayed signal delivery to the sleeping
loop. This manifested as cadence decreases not applying without a
restart - the loop would sleep its full original timeout before
seeing the new cadence.

Fix: _reschedule_adapter now returns the AdapterState to signal,
and _on_config_change signals AFTER releasing the lock. This ensures
immediate event delivery per asyncio semantics.

The lock protects state consistency during config fetches and updates.
The cancel_event is a one-way notification that does not need lock
protection - it simply wakes the sleeping coroutine.

See docs/BUG-CADENCE-DECREASE.md for full investigation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/central/supervisor.py

@@ -396,22 +396,26 @@ class Supervisor:
         self,
         name: str,
         new_config: AdapterConfig,
-    ) -> None:
+    ) -> AdapterState | None:
         """Reschedule an adapter with new configuration.
 
         Maintains rate-limit guarantee: next poll at
         (last_completed_poll + new_cadence_s), not now + new_cadence_s.
+
+        Returns the AdapterState to signal, or None if no signal needed.
+        The caller must signal cancel_event AFTER releasing any locks to
+        ensure immediate event delivery to the sleeping loop.
         """
         state = self._adapter_states.get(name)
         if state is None:
             # Adapter not running - just start it
             await self._start_adapter(new_config)
-            return
+            return None
 
         if not state.is_running:
             # Adapter stopped - restart it
             await self._start_adapter(new_config)
-            return
+            return None
 
         old_cadence = state.config.cadence_s
         new_cadence = new_config.cadence_s
@@ -446,8 +450,9 @@ class Supervisor:
             },
         )
 
-        # Signal the loop to re-evaluate its schedule
+        # Return state so caller can signal OUTSIDE any locks.
-        state.cancel_event.set()
+        # This ensures immediate event delivery to the sleeping loop.
+        return state
 
     async def _on_config_change(self, table: str, key: str) -> None:
         """Handle a configuration change notification.
@@ -463,6 +468,9 @@ class Supervisor:
             extra={"table": table, "key": key},
         )
 
+        # Track state that needs signaling after lock release
+        state_to_signal: AdapterState | None = None
+
         async with self._lock:
             # Fetch the current config for this adapter
             new_config = await self._config_source.get_adapter(adapter_name)
@@ -501,7 +509,13 @@ class Supervisor:
                 )
             else:
                 # Adapter config changed (cadence, settings)
-                await self._reschedule_adapter(adapter_name, new_config)
+                state_to_signal = await self._reschedule_adapter(adapter_name, new_config)
+
+        # Signal OUTSIDE the lock to ensure immediate event delivery.
+        # This fixes cadence-decrease hot-reload where the signal was
+        # delayed by asyncio task scheduling while holding the lock.
+        if state_to_signal is not None:
+            state_to_signal.cancel_event.set()
 
     async def _heartbeat_loop(self) -> None:
         """Publish periodic heartbeats."""