docs(engine): document check_success in MotiveGridGame turn-loop + survived docstring

proteus/game/engine/grid.py

@@ -71,8 +71,9 @@ class MotiveGridGame(ARCBaseGame):
            keeps it in place).
         2. ``scenario.advance_threat`` moves the predator/NPCs.
         3. If ``scenario.check_elimination`` -> :meth:`lose`.
-        4. Else if the step budget is exhausted -> :meth:`win`.
-        5. ``complete_action`` ends the turn.
+        4. Else if ``scenario.check_success`` -> :meth:`win` (early win).
+        5. Else if the step budget is exhausted -> :meth:`win`.
+        6. ``complete_action`` ends the turn.
 
     Boundary handling: arc_grid enforces no world border, so the framework
     guards the grid edge for the focal agent itself.  Every scenario uses
@@ -246,7 +247,7 @@ class MotiveGridGame(ARCBaseGame):
 
     @property
     def survived(self) -> bool:
-        """Whether the focal agent survived the full step budget (win)."""
+        """Whether the focal agent won (survived the step budget or achieved an early goal)."""
         return self._state == GameState.WIN
 
     def current_grid(self) -> np.ndarray: