refactor export limit semantics

backend/tests/test_planning_dispatch_milp.py

@@ -254,6 +254,47 @@ class PlanningDispatchMilpTests(unittest.TestCase):
         self.assertEqual(int(results[0].pv_a_curtailed_w), 5000)
         self.assertGreaterEqual(int(results[0].grid_setpoint_w), 0)
 
+    def test_pv_surplus_export_uses_hard_export_cap(self) -> None:
+        slots = [
+            _slot(load=0, buy=3.0, sell=2.5, pv_a=20_000, pv_b=0),
+        ]
+        battery = _battery()
+        hp = SimpleNamespace(
+            rated_heating_power_w=0,
+            tuv_min_temp_c=45.0,
+            tuv_target_temp_c=55.0,
+        )
+        grid = SimpleNamespace(max_import_power_w=20_000, max_export_power_w=13_500)
+        vehicles = [
+            SimpleNamespace(
+                max_charge_power_w=0,
+                battery_capacity_kwh=1.0,
+                default_target_soc_pct=80.0,
+            ),
+            SimpleNamespace(
+                max_charge_power_w=0,
+                battery_capacity_kwh=1.0,
+                default_target_soc_pct=80.0,
+            ),
+        ]
+        soc0 = battery.soc_max_wh
+        results, _ms = solve_dispatch(
+            slots,
+            battery,
+            hp,
+            grid,
+            [None, None],
+            vehicles,
+            soc0,
+            50.0,
+            tuv_delta_stats=None,
+            operating_mode="AUTO",
+        )
+        self.assertEqual(len(results), 1)
+        self.assertEqual(results[0].export_mode, "PV_SURPLUS")
+        self.assertEqual(results[0].export_limit_w, 13_500)
+        self.assertGreater(results[0].pv_a_curtailed_w, 0)
+
     def test_two_tier_soc_solves_optimal(self) -> None:
         slots = [_slot()]
         battery = _battery()