Clear the Sud Load-rejection Error so it doesn't get replayed as stale

WsServerMultiUser.global_state persists every message ever broadcast
and replays the full accumulated state to any client that subscribes
- by design, so a client connecting fresh or reconnecting mid-run
always gets the same complete picture (see README's new "State replay
on connect" section). That mechanism has no concept of "transient":
the {'Sud': {'Error': ...}} added for Load-rejection got treated as
durable state just like everything else, so any client connecting
after the fact - even one that never touched Load - got the stale
error replayed on connect. Confirmed live before this fix.

tasks/sud.py: send {'Sud': {'Error': None}} immediately after the
error itself, clearing it back to neutral in global_state.

client/brewpi_gui.py: on_sud_changed() treats a falsy Error as a
no-op instead of popping an empty dialog.

README.md: documents the underlying principle (client state replay
on connect, and the corollary that one-shot events need explicit
clearing) under a new Architecture subsection, and refreshes the Sud
channel/forecast sections to match this session's other changes
(Elapsed-based dynamic forecast anchoring instead of wall-clock time
times the nominal warp factor, Load's Error reply).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LhiQe64F74uHV8jzuoSa5K

README.md

@@ -113,6 +113,45 @@ Each component runs inside its own `ATask` at a configurable interval
 keyed WebSocket channel that any connected client can subscribe to and send
 commands back on (e.g. `{"TempCtrl": {"Soll": {"Temp": 65}}}`).
 
+### State replay on connect
+
+A fundamental assumption baked into this protocol: a client never knows what
+it's connecting to. The GUI might be the first thing to ever talk to a
+freshly started server, or it might connect to one that's been running
+unattended for hours, mid-brew, with a schedule already loaded and paused
+partway through step 4. A client can also disconnect (network hiccup, the
+user closing and reopening the GUI) and reconnect later, at any server state,
+with no special "resume" handshake. In every one of these cases, the client
+must end up with the *same* full picture of current state as one that's been
+connected the whole time - not just whatever changes happen after it joins.
+
+This is what `WsServerMultiUser.global_state` (`ws/server/ws_server_multi_user.py`)
+exists for: every message ever broadcast over the dispatcher is merged into
+it (`ws/user.py`'s `update()`), keyed exactly like the live channels are.
+Subscribing to a channel (`{"+": "Sud"}`, sent automatically for every
+channel on connect - see `MessageDispatcherSync(auto_subscribe=True)`)
+doesn't just start a future stream of changes; the server immediately
+replays the *entire* currently-known state for that channel in one message,
+via `User.send()`'s `dpath` search over `global_state`. A reconnecting
+client gets exactly the same replay a brand-new one would, because the
+server doesn't distinguish between the two cases at all - there's no
+"first connect" special-casing anywhere in this path.
+
+The corollary, easy to miss: this mechanism has no concept of "transient" -
+anything sent through it is implicitly durable state that will be replayed
+to whoever connects next, even long after the fact. A one-shot *event*
+(something that happened, rather than something that's currently true) has
+to be modeled as a value that gets explicitly cleared back to neutral right
+after sending, or it will linger in `global_state` and get handed to some
+unrelated future client as if it just happened to them. `tasks/sud.py`'s
+`SudTask.recv()` hit this directly: a `Load` rejected because a run is in
+progress sends `{"Sud": {"Error": "..."}}` to explain why, immediately
+followed by `{"Sud": {"Error": None}}` to clear it - without that second
+send, every client connecting afterwards, no matter how much later or how
+unrelated to the rejected `Load`, would immediately see that same stale
+error on connect. The client mirrors this by treating a falsy `Error` as a
+no-op rather than an empty dialog.
+
 ## Requirements
 
 - Python 3.8+
@@ -217,12 +256,17 @@ controller's `theta_soll`/`heatrate_soll` toward each step's target
 tolerance), counts down hold steps' `duration`, and applies each step's
 `stirrer` block (`interval_time`/
 `on_ratio` map directly onto the stirrer's cycle time/duty cycle). It
-exposes progress (current step, remaining hold time, state, any
+exposes progress (current step, remaining hold time, elapsed run time -
-`user_message`) on the `"Sud"` WebSocket channel and accepts
+tick-counted, not derived from wall-clock time times the warp factor, since
+the latter is only nominal and drifts under real scheduling load - state,
+any `user_message`) on the `"Sud"` WebSocket channel and accepts
 `{"Sud": {"Start": true}}` to begin the schedule (also restarts one that's
 already finished), `{"Sud": {"Pause": true}}` to freeze progress without
-losing it, and `{"Sud": {"Confirm": true}}` to acknowledge a pause and move
+losing it, `{"Sud": {"Confirm": true}}` to acknowledge a pause and move to
-to the next step.
+the next step, and `{"Sud": {"Load": <sud.json contents>}}` to replace the
+running schedule - refused (with an explicit, one-shot `Error` reply - see
+"State replay on connect" above) while a run is already in progress, rather
+than the client trying to guess that from its own view of the state.
 
 The temperature controller has a master enabled switch (off by default -
 see `components/pid/temp_controller_base.py`): `SudTask` enables it for as
@@ -249,8 +293,10 @@ The GUI's Automatic tab shows up to three time estimates for a schedule:
   second since it's pure CPU-bound iteration, no real time/IO involved. This
   replaces the naive preview a moment after a schedule is loaded.
 - Once running, a *dynamic* one: the already-elapsed part is the actual
-  measured trace, and only the remaining steps are re-projected from the
+  measured trace, plotted against `Sud.elapsed` (see "State replay on
-  live temperature/step/`hold_remaining` each tick.
+  connect" above) rather than wall-clock time, and only the remaining steps
+  are re-projected from the live temperature/step/`hold_remaining` each
+  tick.
 
 The naive estimate is structurally optimistic - it assumes the plant
 instantly tracks the declared rate and that "reached" is instant once the
@@ -265,7 +311,14 @@ finishes - if the two diverge by far more than that, suspect a real control
 issue rather than a forecasting one (see the `HoldCool` threshold note in
 `components/pid/temp_controller_base.py` - too tight a threshold there once
 caused exactly this kind of large, otherwise-unexplained gap, by making the
-controller chatter in and out of `COOL` and never actually converge).
+controller chatter in and out of `COOL` and never actually converge). Rule
+out a *display* artifact first, though: the dynamic trace used to position
+itself using wall-clock time times the configured `sim_warp_factor`, but
+that factor is only nominal - real asyncio/Python scheduling overhead means
+the actually-achieved speedup runs measurably below it (confirmed: ~80x
+instead of a configured 100x), which alone produced a divergence large
+enough to look like a control problem. `Sud.elapsed` (tick-counted, immune
+to wall-clock pacing) replaced that reconstruction for exactly this reason.
 
 ## Logging & analysis
 

client/brewpi_gui.py

@@ -880,7 +880,13 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			elif "Forecast" in key:
 				self.on_sud_forecast_received(msg['Forecast'])
 			elif "Error" in key:
-				QtWidgets.QMessageBox.warning(self, "Sud", msg['Error'])
+				# The server clears this back to None right after sending
+				# it (see tasks/sud.py's recv()) so it doesn't linger in
+				# global_state and get replayed as stale to a client
+				# connecting later - the clearing message itself must be
+				# a no-op here, not an empty dialog.
+				if msg['Error']:
+					QtWidgets.QMessageBox.warning(self, "Sud", msg['Error'])
 		self.update_sud_actions()
 
 	def on_sud_forecast_received(self, forecast):

tasks/sud.py

@@ -202,7 +202,17 @@ class SudTask(ATask):
 					# silently dropping the request. The client has no
 					# business pre-emptively guessing this itself from its
 					# own (replicated, laggy) view of the state.
+					#
+					# Immediately cleared back to None - unlike every other
+					# field here, this is a one-shot event, not state. The
+					# dispatcher has no concept of "don't persist this into
+					# global_state" (see ws/user.py's update()), so without
+					# clearing it, any client connecting later - even one
+					# that never touched Load - would get this stale error
+					# replayed on connect, with nothing it just did to
+					# explain why.
 					await self.send({'Error': 'Cannot load a new schedule while a run is in progress - stop it first.'})
+					await self.send({'Error': None})
 
 	async def send(self, data):
 		await self.msg_handler.send(data)