Show user_message as a modal dialog when the Sud waits for confirmation

Adds a thread-safe path from on_sud_changed() (websocket recv thread)
to a modal QMessageBox on the GUI thread via Qt's cross-thread
signal/slot queuing, fired when the State transition lands on
WAIT_USER - which the schedule is already blocked on server-side, so
the dialog just gives it a UI: closing it (OK) sends Confirm.

Deliberately scoped to WAIT_USER transitions, not every UserMessage -
most steps in sude/sud_0010.json inherit the schedule's default
placeholder text ("Put user message here") rather than overriding it,
so popping a dialog for every step would mostly show that placeholder.

client/brewpi_gui.py

@@ -19,6 +19,7 @@ import asyncio
 # str(SudState.X) values (as sent in the 'State' message) that count as
 # "running" for enabling/disabling the Start/Pause/Stop toolbar actions.
 SUD_RUNNING_STATES = {"SudState.RAMPING", "SudState.HOLDING", "SudState.WAIT_USER"}
+SUD_WAIT_USER_STATE = "SudState.WAIT_USER"
 SUD_PAUSED_STATE = "SudState.PAUSED"
 
 
@@ -169,9 +170,16 @@ class SudForecastPlot(FigureCanvasQTAgg):
 
 
 class Window(QtWidgets.QMainWindow, Ui_MainWindow):
+	# on_sud_changed() runs on the websocket recv thread, but a modal dialog
+	# must be shown from the GUI thread - a signal/slot crosses that thread
+	# boundary safely (Qt auto-queues the slot call onto the receiver's
+	# thread when sender and receiver differ).
+	user_message_signal = QtCore.pyqtSignal(str)
+
 	def __init__(self):
 		QtWidgets.QMainWindow.__init__(self)
 		self.setWindowIcon(QtGui.QIcon('res/beer.png'))
+		self.user_message_signal.connect(self.on_user_message_signal)
 
 		loop = asyncio.new_event_loop()
 		asyncio.set_event_loop(loop)
@@ -181,6 +189,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.connected = False
 		self.sud_loaded = False
 		self.sud_state = None
+		self.sud_user_message = None
 		# time.monotonic() of the last IDLE/DONE -> running transition, used
 		# to position the forecast plot's progress line; None while not
 		# running. sud_paused_total accumulates time spent PAUSED so the
@@ -304,6 +313,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			# Nothing reported over a dead connection can be trusted anymore.
 			self.sud_loaded = False
 			self.sud_state = None
+			self.sud_user_message = None
 			self.sud_start_time = None
 			self.sud_paused_total = 0.0
 			self.sud_pause_started_at = None
@@ -352,6 +362,13 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 	def on_action_sud_stop(self):
 		self.msg_sud.send({'Stop': True})
 
+	def on_user_message_signal(self, message):
+		# Runs on the GUI thread (queued there by the cross-thread signal
+		# emit in on_sud_changed()). The Sud is already blocked in
+		# WAIT_USER server-side; closing this dialog is what unblocks it.
+		QtWidgets.QMessageBox.information(self, "Sud", message)
+		self.msg_sud.send({'Confirm': True})
+
 	def on_action_sud_save(self):
 		# Pick the destination up front, on the GUI thread - the actual
 		# write happens in on_sud_changed(), which runs off a worker thread
@@ -482,6 +499,11 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 					self.sud_start_time = None
 					self.sud_paused_total = 0.0
 					self.sud_pause_started_at = None
+
+				if self.sud_state == SUD_WAIT_USER_STATE and prev_state != SUD_WAIT_USER_STATE and self.sud_user_message:
+					self.user_message_signal.emit(self.sud_user_message)
+			elif "UserMessage" in key:
+				self.sud_user_message = msg['UserMessage']
 			elif "Step" in key:
 				step = msg['Step']
 				descr = step.get('Descr')