Expose heat exchanger diagnostics and retune conductance

src/reactor_sim/state.py

@@ -75,6 +75,8 @@ class PlantState:
     secondary_pumps: list[PumpState] = field(default_factory=list)
     generators: list[GeneratorState] = field(default_factory=list)
     aux_draws: dict[str, float] = field(default_factory=dict)
+    heat_exchanger_efficiency: float = 0.0
+    primary_to_secondary_delta_t: float = 0.0
     time_elapsed: float = field(default=0.0)
 
     def snapshot(self) -> dict[str, float]:
@@ -115,6 +117,8 @@ class PlantState:
         generators_blob = data.get("generators", [])
         generators = [GeneratorState(**g) for g in generators_blob]
         aux_draws = data.get("aux_draws", {})
+        hx_eff = data.get("heat_exchanger_efficiency", 0.0)
+        delta_t = data.get("primary_to_secondary_delta_t", 0.0)
         return cls(
             core=CoreState(**core_blob, fission_product_inventory=inventory, emitted_particles=particles),
             primary_loop=CoolantLoopState(**data["primary_loop"]),
@@ -124,5 +128,7 @@ class PlantState:
             secondary_pumps=[PumpState(**p) for p in sec_pumps_blob],
             generators=generators,
             aux_draws=aux_draws,
+            heat_exchanger_efficiency=hx_eff,
+            primary_to_secondary_delta_t=delta_t,
             time_elapsed=data.get("time_elapsed", 0.0),
         )