Derive Pot's M/C from pot/grain/water mass instead of hardcoding them

Add Sud.derive_plant_params(), which combines pot_mass/pot_material/
grain_mass/water_mass into a single lumped (mass, specific heat) pair
using approximate specific-heat constants for water, grain, and (by a
small material lookup table) the pot itself. demo_sud.py now builds
its plant_params from this instead of hardcoded C/M values, keeping
L/Td as the only manually-tuned plant parameters.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/sud.py

@@ -2,6 +2,15 @@ import json
 from enum import Enum
 from utils.value import AttributeChange
 
+# Specific heat capacities [J/(kg*K)] used to derive a single lumped
+# (mass, specific heat) pair for the pot's contents from pot_mass/
+# grain_mass/water_mass. Approximate, typical values.
+SPECIFIC_HEAT_WATER = 4190
+SPECIFIC_HEAT_GRAIN = 1800
+SPECIFIC_HEAT_BY_MATERIAL = {
+	"Edelstahl 18/10": 500,
+}
+
 
 class SudState(Enum):
 	IDLE = 0
@@ -21,12 +30,31 @@ class Sud(AttributeChange):
 		self.description = data.get('Description', '')
 		self.schedule = data['schedule']
 
+		self.pot_mass = data.get('pot_mass', 0)
+		self.pot_material = data.get('pot_material')
+		self.grain_mass = data.get('grain_mass', 0)
+		self.water_mass = data.get('water_mass', 0)
+
 		self.index = -1
 		self.hold_remaining = 0.0
 		self.state = SudState.IDLE
 		self.step = None
 		self.user_message = None
 
+	def derive_plant_params(self):
+		"""Lumped (mass, specific heat) lifted from pot_mass/pot_material/
+		grain_mass/water_mass, for use as Pot's "M"/"C" params."""
+		c_pot = SPECIFIC_HEAT_BY_MATERIAL.get(self.pot_material, SPECIFIC_HEAT_WATER)
+		mass = self.water_mass + self.grain_mass + self.pot_mass
+		capacitance = (self.water_mass * SPECIFIC_HEAT_WATER
+			+ self.grain_mass * SPECIFIC_HEAT_GRAIN
+			+ self.pot_mass * c_pot)
+
+		return {
+			'M': mass,
+			'C': capacitance / mass if mass > 0 else SPECIFIC_HEAT_WATER,
+		}
+
 	def start(self):
 		if self.state != SudState.IDLE:
 			return