fix solar sell pri male zaporne cene

backend/tests/test_planning_dispatch_milp.py

@@ -782,6 +782,63 @@ class PlanningDispatchMilpTests(unittest.TestCase):
             msg="with very negative buy price, solver may choose to exceed breaker (soft cap)",
         )
 
+    def test_block_export_on_negative_sell_no_grid_export_pv_surplus(self) -> None:
+        """site_grid_connection.block_export_on_negative_sell → ge=0 při sell<0."""
+        slots = [
+            PlanningSlot(
+                interval_start=datetime(2026, 4, 3, 12, 0, tzinfo=timezone.utc),
+                buy_price=5.25,
+                sell_price=-0.5,
+                pv_a_forecast_w=7000,
+                pv_b_forecast_w=0,
+                load_baseline_w=500,
+                ev1_connected=False,
+                ev2_connected=False,
+                is_predicted_price=False,
+                allow_charge=True,
+                allow_discharge_export=False,
+            )
+        ]
+        battery = _battery(uc_wh=20_000.0, arb_pct=15.0, max_pct=95.0)
+        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=17_000,
+            max_export_power_w=8000,
+            block_export_on_negative_sell=True,
+        )
+        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 = 0.34 * battery.usable_capacity_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.assertGreaterEqual(results[0].grid_setpoint_w, 0, "no grid export")
+        self.assertGreater(results[0].battery_setpoint_w, 0, "surplus PV should charge")
+
 
 class TerminalSocShadowTests(unittest.TestCase):
     """Terminal SoC shadow price v objective drží konec horizontu nad holým minimem."""