feat: add reactor control persistence and tests

src/reactor_sim/coolant.py

@@ -0,0 +1,27 @@
+"""Coolant loop control models."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+import logging
+
+from .state import CoolantLoopState
+
+LOGGER = logging.getLogger(__name__)
+
+
+@dataclass
+class Pump:
+    nominal_flow: float
+    efficiency: float = 0.9
+
+    def flow_rate(self, demand: float) -> float:
+        demand = max(0.0, min(1.0, demand))
+        return self.nominal_flow * (0.2 + 0.8 * demand) * self.efficiency
+
+    def step(self, loop: CoolantLoopState, demand: float) -> None:
+        loop.mass_flow_rate = self.flow_rate(demand)
+        loop.pressure = 12.0 * demand + 2.0
+        LOGGER.debug(
+            "Pump demand=%.2f -> %.0f kg/s, pressure=%.1f MPa", demand, loop.mass_flow_rate, loop.pressure
+        )