Derive Pot's L/Td from the Sud doc instead of a fixed server default

Sud now parses top-level L/Td fields from sude/*.json (defaulting to 0.2/30,
matching the old hardcoded server constants), and derive_plant_params()
returns them alongside M/C - constant for the whole brew, unlike M/C which
vary per step with grain/water mass. All sude/*.json docs gain explicit
L/Td fields.

Callers (tasks/sud.py, SudForecastEstimator, demo_sud.py) switch from the
narrow set_thermal_params(M, C)/set_model_params(M, C) to the full
set_plant_params(params)/set_model_plant_params(params), since
derive_plant_params() now always returns all four keys; both narrow setters
are removed as dead code.

Caught along the way: Pot.set_plant_params() unconditionally rebuilt the
Delay ring buffer, which was harmless when only ever called once at
construction - but now running on every Sud step change, it was wiping
in-flight delayed power at each step boundary. Fixed to only rebuild when
Td actually changes; verified this restores the exact original forecast
result for sud_0010.json.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DkkuG48uHFCGKe6dPSERFk

components/sud.py

@@ -61,6 +61,11 @@ EMPTY_SUD = {
 	'Description': '',
 	'pot_mass': 0,
 	'pot_material': None,
+	# Pot energy loss coefficient [W/(kg*K)] and transport propagation
+	# delay [s] - see derive_plant_params(). Defaults match the generic
+	# values brewpi.py used to hardcode for every brew alike.
+	'L': 0.2,
+	'Td': 30,
 	'steps': [],
 }
 
@@ -74,8 +79,8 @@ class Sud(AttributeChange):
 		AttributeChange.__init__(self)
 		self._data = EMPTY_SUD
 
-		(self.name, self.description, self.schedule,
-			self.pot_mass, self.pot_material) = self._parse_data(self._data)
+		(self.name, self.description, self.schedule, self.pot_mass,
+			self.pot_material, self.L, self.Td) = self._parse_data(self._data)
 
 		self._paused_from = None
 		self._reset_run_state()
@@ -83,9 +88,9 @@ class Sud(AttributeChange):
 	@staticmethod
 	def _parse_data(data):
 		"""Parses a sud.json document into the (name, description, schedule,
-		pot_mass, pot_material) tuple Sud needs. Computed up front rather
-		than assigned straight onto self, so a malformed load() can't
-		leave a half-applied schedule in place."""
+		pot_mass, pot_material, L, Td) tuple Sud needs. Computed up front
+		rather than assigned straight onto self, so a malformed load()
+		can't leave a half-applied schedule in place."""
 		name = data.get('Name', '')
 		description = data.get('Description', '')
 
@@ -94,8 +99,10 @@ class Sud(AttributeChange):
 
 		pot_mass = data.get('pot_mass', 0)
 		pot_material = data.get('pot_material')
+		L = data.get('L', EMPTY_SUD['L'])
+		Td = data.get('Td', EMPTY_SUD['Td'])
 
-		return name, description, schedule, pot_mass, pot_material
+		return name, description, schedule, pot_mass, pot_material, L, Td
 
 	def _reset_run_state(self):
 		"""Resets run-time progress back to a freshly-loaded, not-yet-started
@@ -128,18 +135,20 @@ class Sud(AttributeChange):
 		except (KeyError, TypeError):
 			return False
 
-		self.name, self.description, self.schedule, self.pot_mass, self.pot_material = parsed
+		(self.name, self.description, self.schedule, self.pot_mass,
+			self.pot_material, self.L, self.Td) = parsed
 		self._data = data
 
 		self._reset_run_state()
 		return True
 
 	def derive_plant_params(self, grain_mass, water_mass):
-		"""Lumped (mass, specific heat) lifted from pot_mass/pot_material and
-		the current step's grain_mass/water_mass, for use as Pot's "M"/"C"
-		params. grain_mass/water_mass vary per step (e.g. malt going in,
-		water boiling off), so this is recomputed on every step change
-		rather than once at startup."""
+		"""Full Pot plant params - "M"/"C" lumped (mass, specific heat)
+		from pot_mass/pot_material and the current step's grain_mass/
+		water_mass (these vary per step, e.g. malt going in, water
+		boiling off, so this is recomputed on every step change rather
+		than once at startup), plus "L"/"Td" straight from this Sud's
+		own doc (constant for the whole brew - see Sud.load())."""
 		c_pot = SPECIFIC_HEAT_BY_MATERIAL.get(self.pot_material, SPECIFIC_HEAT_WATER)
 		mass = water_mass + grain_mass + self.pot_mass
 		capacitance = (water_mass * SPECIFIC_HEAT_WATER
@@ -149,6 +158,8 @@ class Sud(AttributeChange):
 		return {
 			'M': mass,
 			'C': capacitance / mass if mass > 0 else SPECIFIC_HEAT_WATER,
+			'L': self.L,
+			'Td': self.Td,
 		}
 
 	def start(self):