Fix adding and removing waypoints in the UI.

This moves more of the logic out of the UI so mypy can actually spot
these mistakes more often.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/2495.

game/ato/flight.py

@@ -91,6 +91,12 @@ class Flight(SidcDescribable):
     def flight_plan(self) -> FlightPlan[Any]:
         return self._flight_plan_builder.get_or_build()
 
+    def degrade_to_custom_flight_plan(self) -> None:
+        from .flightplans.custom import Builder as CustomBuilder
+
+        self._flight_plan_builder = CustomBuilder(self, self.flight_plan.waypoints[1:])
+        self.recreate_flight_plan()
+
     def __getstate__(self) -> dict[str, Any]:
         state = self.__dict__.copy()
         # Avoid persisting the flight state since that's not (currently) used outside

game/ato/flightplans/custom.py

@@ -8,6 +8,7 @@ from typing import TYPE_CHECKING, Type
 from .flightplan import FlightPlan, Layout
 from .ibuilder import IBuilder
 from .waypointbuilder import WaypointBuilder
+from .. import Flight
 from ..flightwaypointtype import FlightWaypointType
 
 if TYPE_CHECKING:
@@ -55,9 +56,17 @@ class CustomFlightPlan(FlightPlan[CustomLayout]):
 
 
 class Builder(IBuilder[CustomFlightPlan, CustomLayout]):
+    def __init__(
+        self, flight: Flight, waypoints: list[FlightWaypoint] | None = None
+    ) -> None:
+        super().__init__(flight)
+        if waypoints is None:
+            waypoints = []
+        self.waypoints = waypoints
+
     def layout(self) -> CustomLayout:
         builder = WaypointBuilder(self.flight, self.coalition)
-        return CustomLayout(builder.takeoff(self.flight.departure), [])
+        return CustomLayout(builder.takeoff(self.flight.departure), self.waypoints)
 
     def build(self) -> CustomFlightPlan:
         return CustomFlightPlan(self.flight, self.layout())