fix: heater task permanently died after a mid-brew unplug, never recovered

Root cause (from the brewpi Pi's log): HendiCtrl.disconnect() only
caught HendiException (a protocol-level NAK), but a genuine unplug
fails deep inside pyserial itself - flushInput()/readline() raise
termios.error/OSError on the now-dead fd. That escaped disconnect()
uncaught (skipping self.ser.close() too), then kept propagating up
through every caller that invoked disconnect() from its own except
handler (HeaterHendi.process()/activate(), AHeater.open()'s
context-manager exit), all the way out of HeaterTask.on_process()'s
coroutine entirely. Nothing restarts a dead ATask, so the heater's
process()/duty-cycle loop was gone for the rest of the process's
life - reconnecting afterward changed `connected` back to True but
nothing was left running to ever call process() again.

Fixes:
- HendiCtrl.disconnect() now catches broadly and always closes the
  port, matching Pololu1376.disconnect()'s already-correct pattern.
- HeaterTask/StirrerTask.on_process() gain an outer retry loop as a
  safety net: even an unanticipated exception now logs, marks
  disconnected, and re-enters rather than permanently killing the
  task.

Verified by reproducing the exact failure (comm error raising a raw
OSError, not HendiException) against a fake device - the task now
survives and resumes process()ing once reconnected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YaPLuRPpyjWcwhMvCvpHCL

tasks/stirrer.py

@@ -66,11 +66,24 @@ class StirrerTask(ATask):
 		# observer.
 		await self.send({'Connected': self.device.connected})
 
-		with self.device.open():
-			while True:
+		# Outer retry loop - see HeaterTask.on_process()'s own comment for
+		# why: nothing restarts a dead ATask, so an exception escaping this
+		# coroutine entirely would permanently stop this device from ever
+		# being process()'d again, even after a later successful reconnect.
+		while True:
+			try:
+				with self.device.open():
+					while True:
+						try:
+							self.device.process()
+						except Exception as e:
+							print(f"StirrerTask: comm error, marking disconnected: {e}")
+							self.device.disconnect()
+						await asyncio.sleep(self.interval)
+			except Exception as e:
+				print(f"StirrerTask: unexpected error, recovering: {e}")
 				try:
-					self.device.process()
-				except Exception as e:
-					print(f"StirrerTask: comm error, marking disconnected: {e}")
 					self.device.disconnect()
+				except Exception:
+					pass
 				await asyncio.sleep(self.interval)