Add shared snapshot helper and simulation snapshot mode

src/reactor_sim/simulation.py

@@ -96,6 +96,9 @@ def main() -> None:
     configure_logging(log_level, log_file)
     realtime = os.getenv("FISSION_REALTIME", "0") == "1"
     alternate_dashboard = os.getenv("ALTERNATE_DASHBOARD", "0") == "1"
+    snapshot_at_env = os.getenv("FISSION_SNAPSHOT_AT")
+    snapshot_at = float(snapshot_at_env) if snapshot_at_env else None
+    snapshot_path = os.getenv("FISSION_SNAPSHOT_PATH", "artifacts/snapshot.txt")
     duration_env = os.getenv("FISSION_SIM_DURATION")
     if duration_env:
         duration = None if duration_env.lower() in {"none", "infinite"} else float(duration_env)
@@ -117,7 +120,7 @@ def main() -> None:
     save_path = os.getenv("FISSION_SAVE_STATE") or str(state_path)
     if load_path:
         sim.start_state = reactor.load_state(load_path)
-    if dashboard_mode:
+    if dashboard_mode and snapshot_at is None:
         if alternate_dashboard:
             try:
                 from .textual_dashboard import run_textual_dashboard
@@ -143,7 +146,17 @@ def main() -> None:
             dashboard.run()
             return
     try:
-        if realtime:
+        if snapshot_at is not None:
+            sim.duration = snapshot_at
+            LOGGER.info("Running headless to t=%.1fs for snapshot...", snapshot_at)
+            for _ in sim.run():
+                pass
+            if sim.last_state:
+                from .snapshot import write_snapshot
+
+                write_snapshot(snapshot_path, reactor, sim.last_state)
+                LOGGER.info("Snapshot written to %s", snapshot_path)
+        elif realtime:
             LOGGER.info("Running in real-time mode (Ctrl+C to stop)...")
             for _ in sim.run():
                 pass

src/reactor_sim/snapshot.py

@@ -0,0 +1,53 @@
+"""Snapshot formatting helpers shared across dashboards."""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import Iterable
+
+from . import constants
+from .reactor import Reactor
+from .state import PlantState
+
+
+def snapshot_lines(reactor: Reactor, state: PlantState) -> list[str]:
+    core = state.core
+    prim = state.primary_loop
+    sec = state.secondary_loop
+    t0 = state.turbines[0] if state.turbines else None
+    lines: list[str] = [
+        f"Time {state.time_elapsed:6.1f}s",
+        f"Core: {core.power_output_mw:6.1f}MW fuel {core.fuel_temperature:6.1f}K rods {reactor.control.rod_fraction:.3f} ({'AUTO' if not reactor.control.manual_control else 'MAN'})",
+        f"Primary: P={prim.pressure:4.1f}/{constants.MAX_PRESSURE:4.1f}MPa Tin={prim.temperature_in:6.1f}K Tout={prim.temperature_out:6.1f}K Flow={prim.mass_flow_rate:6.0f}kg/s",
+        f"Secondary: P={sec.pressure:4.1f}/{constants.MAX_PRESSURE:4.1f}MPa Tin={sec.temperature_in:6.1f}K Tout={sec.temperature_out:6.1f}K q={sec.steam_quality:4.2f} Flow={sec.mass_flow_rate:6.0f}kg/s",
+        f"HX ΔT={state.primary_to_secondary_delta_t:4.0f}K Eff={state.heat_exchanger_efficiency*100:5.1f}%",
+    ]
+    if t0:
+        lines.append(
+            f"Turbines: h={t0.steam_enthalpy:5.0f}kJ/kg avail={_steam_available_power(state):5.1f}MW "
+            f"CondP={t0.condenser_pressure:4.2f}/{constants.CONDENSER_MAX_PRESSURE_MPA:4.2f}MPa "
+            f"CondT={t0.condenser_temperature:6.1f}K"
+        )
+        lines.append("Outputs: " + " ".join([f"T{idx+1}:{t.electrical_output_mw:5.1f}MW" for idx, t in enumerate(state.turbines)]))
+    failures = ", ".join(reactor.health_monitor.failure_log) if reactor.health_monitor.failure_log else "None"
+    lines.append(
+        f"Status: pumps pri {[p.status for p in state.primary_pumps]} sec {[p.status for p in state.secondary_pumps]} "
+        f"relief pri={'OPEN' if reactor.primary_relief_open else 'CLOSED'} sec={'OPEN' if reactor.secondary_relief_open else 'CLOSED'} "
+        f"failures={failures}"
+    )
+    return lines
+
+
+def write_snapshot(path: Path | str, reactor: Reactor, state: PlantState) -> None:
+    p = Path(path)
+    p.parent.mkdir(parents=True, exist_ok=True)
+    p.write_text("\n".join(snapshot_lines(reactor, state)))
+
+
+def _steam_available_power(state: PlantState) -> float:
+    mass_flow = state.secondary_loop.mass_flow_rate * max(0.0, state.secondary_loop.steam_quality)
+    if mass_flow <= 1.0:
+        return 0.0
+    enthalpy = state.turbines[0].steam_enthalpy if state.turbines else (constants.STEAM_LATENT_HEAT / 1_000.0)
+    return (enthalpy * mass_flow) / 1_000.0
+

src/reactor_sim/textual_dashboard.py

@@ -18,6 +18,7 @@ from .reactor import Reactor
 from .simulation import ReactorSimulation
 from .state import PlantState
 from .commands import ReactorCommand
+from .snapshot import snapshot_lines
 
 LOGGER = logging.getLogger(__name__)
 
@@ -431,31 +432,7 @@ class TextualDashboard(App):
         return (enthalpy * mass_flow) / 1_000.0
 
     def _snapshot_lines(self) -> list[str]:
-        core = self.state.core
-        prim = self.state.primary_loop
-        sec = self.state.secondary_loop
-        t0 = self.state.turbines[0] if self.state.turbines else None
-        lines = [
-            f"Time {self.state.time_elapsed:6.1f}s",
-            f"Core: {core.power_output_mw:6.1f}MW fuel {core.fuel_temperature:6.1f}K rods {self.reactor.control.rod_fraction:.3f} ({'AUTO' if not self.reactor.control.manual_control else 'MAN'})",
-            f"Primary: P={prim.pressure:4.1f}/{constants.MAX_PRESSURE:4.1f}MPa Tin={prim.temperature_in:6.1f}K Tout={prim.temperature_out:6.1f}K Flow={prim.mass_flow_rate:6.0f}kg/s",
-            f"Secondary: P={sec.pressure:4.1f}/{constants.MAX_PRESSURE:4.1f}MPa Tin={sec.temperature_in:6.1f}K Tout={sec.temperature_out:6.1f}K q={sec.steam_quality:4.2f} Flow={sec.mass_flow_rate:6.0f}kg/s",
-            f"HX ΔT={self.state.primary_to_secondary_delta_t:4.0f}K Eff={self.state.heat_exchanger_efficiency*100:5.1f}%",
-        ]
-        if t0:
-            lines.append(
-                f"Turbines: h={t0.steam_enthalpy:5.0f}kJ/kg avail={self._steam_available_power(self.state):5.1f}MW "
-                f"CondP={t0.condenser_pressure:4.2f}/{constants.CONDENSER_MAX_PRESSURE_MPA:4.2f}MPa "
-                f"CondT={t0.condenser_temperature:6.1f}K"
-            )
-            lines.append("Outputs: " + " ".join([f"T{idx+1}:{t.electrical_output_mw:5.1f}MW" for idx, t in enumerate(self.state.turbines)]))
-        failures = ", ".join(self.reactor.health_monitor.failure_log) if self.reactor.health_monitor.failure_log else "None"
-        lines.append(
-            f"Status: pumps pri {[p.status for p in self.state.primary_pumps]} sec {[p.status for p in self.state.secondary_pumps]} "
-            f"relief pri={'OPEN' if self.reactor.primary_relief_open else 'CLOSED'} sec={'OPEN' if self.reactor.secondary_relief_open else 'CLOSED'} "
-            f"failures={failures}"
-        )
-        return lines
+        return snapshot_lines(self.reactor, self.state)
 
     def _save_snapshot(self, auto: bool = False) -> None:
         try: