From 2c3f9e3b4524eee07f050d127dcf66cf54f190eb Mon Sep 17 00:00:00 2001
From: Codex Agent <codex@example.com>
Date: Sun, 23 Nov 2025 23:12:13 +0100
Subject: [PATCH] Quantize manual rod steps to 0.025

---
 src/reactor_sim/constants.py |  1 +
 src/reactor_sim/control.py   |  7 ++++++-
 src/reactor_sim/dashboard.py |  8 +++++---
 tests/test_control.py        | 40 ++++++++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+), 4 deletions(-)
 create mode 100644 tests/test_control.py

diff --git a/src/reactor_sim/constants.py b/src/reactor_sim/constants.py
index 354b693..d8df13d 100644
--- a/src/reactor_sim/constants.py
+++ b/src/reactor_sim/constants.py
@@ -14,6 +14,7 @@ MAX_PRESSURE = 15.0  # MPa typical PWR primary loop limit
 CONTROL_ROD_SPEED = 0.03  # fraction insertion per second
 CONTROL_ROD_WORTH = 0.042  # delta rho contribution when fully withdrawn
 CONTROL_ROD_BANK_WEIGHTS = (0.4, 0.35, 0.25)
+ROD_MANUAL_STEP = 0.025
 STEAM_TURBINE_EFFICIENCY = 0.34
 GENERATOR_EFFICIENCY = 0.96
 ENVIRONMENT_TEMPERATURE = 295.0  # K
diff --git a/src/reactor_sim/control.py b/src/reactor_sim/control.py
index c1328ec..f4456d6 100644
--- a/src/reactor_sim/control.py
+++ b/src/reactor_sim/control.py
@@ -45,7 +45,7 @@ class ControlSystem:
         return self.rod_fraction
 
     def set_rods(self, fraction: float) -> float:
-        self.rod_target = clamp(fraction, 0.0, 0.95)
+        self.rod_target = self._quantize_manual(fraction)
         self._advance_banks(self.rod_target, 0.0)
         LOGGER.info("Manual rod target set to %.3f", self.rod_target)
         return self.rod_target
@@ -127,6 +127,11 @@ class ControlSystem:
     def _sync_fraction(self) -> None:
         self.rod_fraction = self.effective_insertion()
 
+    def _quantize_manual(self, fraction: float) -> float:
+        step = constants.ROD_MANUAL_STEP
+        quantized = round(fraction / step) * step
+        return clamp(quantized, 0.0, 0.95)
+
 
     def save_state(
         self,
diff --git a/src/reactor_sim/dashboard.py b/src/reactor_sim/dashboard.py
index f00ee5b..b6ee139 100644
--- a/src/reactor_sim/dashboard.py
+++ b/src/reactor_sim/dashboard.py
@@ -177,10 +177,10 @@ class ReactorDashboard:
                 self._toggle_turbine_unit(idx)
             elif ch in (ord("+"), ord("=")):
                 # Insert rods (increase fraction)
-                self._queue_command(ReactorCommand(rod_position=self._clamped_rod(0.05)))
+                self._queue_command(ReactorCommand(rod_position=self._clamped_rod(constants.ROD_MANUAL_STEP)))
             elif ch == ord("-"):
                 # Withdraw rods (decrease fraction)
-                self._queue_command(ReactorCommand(rod_position=self._clamped_rod(-0.05)))
+                self._queue_command(ReactorCommand(rod_position=self._clamped_rod(-constants.ROD_MANUAL_STEP)))
             elif ch == ord("["):
                 demand = self._current_demand() - 50.0
                 self._queue_command(ReactorCommand(consumer_demand=max(0.0, demand)))
@@ -710,7 +710,9 @@ class ReactorDashboard:
 
     def _clamped_rod(self, delta: float) -> float:
         new_fraction = self.reactor.control.rod_fraction + delta
-        return max(0.0, min(0.95, new_fraction))
+        step = constants.ROD_MANUAL_STEP
+        quantized = round(new_fraction / step) * step
+        return max(0.0, min(0.95, quantized))
 
     def _install_log_capture(self) -> None:
         if self._log_handler:
diff --git a/tests/test_control.py b/tests/test_control.py
new file mode 100644
index 0000000..91d0317
--- /dev/null
+++ b/tests/test_control.py
@@ -0,0 +1,40 @@
+import pytest
+
+from reactor_sim.control import ControlSystem
+from reactor_sim import constants
+from reactor_sim.state import CoreState
+
+
+def _core_state() -> CoreState:
+    return CoreState(
+        fuel_temperature=300.0,
+        neutron_flux=1e5,
+        reactivity_margin=0.0,
+        power_output_mw=0.0,
+        burnup=0.0,
+    )
+
+
+def test_manual_rods_quantized_to_step():
+    control = ControlSystem()
+    control.manual_control = True
+    core = _core_state()
+
+    control.set_rods(0.333)
+    assert control.rod_target == 0.325
+    control.update_rods(core, dt=100.0)
+    assert control.rod_fraction == pytest.approx(0.325, rel=1e-6)
+
+    control.increment_rods(0.014)
+    assert control.rod_target == pytest.approx(0.35)
+    control.update_rods(core, dt=100.0)
+    assert control.rod_fraction == pytest.approx(0.35, rel=1e-6)
+
+    # Clamp upper bound
+    control.set_rods(1.0)
+    control.update_rods(core, dt=100.0)
+    assert control.rod_fraction == 0.95
+
+
+def test_dashboard_step_constant_exposed():
+    assert constants.ROD_MANUAL_STEP == 0.025