feat: actually add to protocol api

somehow i forgot to do this

api/src/opentrons/protocol_api/core/legacy/legacy_well_core.py

@@ -114,6 +114,10 @@ def load_liquid(
         """Load liquid into a well."""
         raise APIVersionError(api_element="Loading a liquid")
 
+    def load_empty(self) -> None:
+        """Mark a well as empty."""
+        assert False, "load_empty only supported on engine core"
+
     def from_center_cartesian(self, x: float, y: float, z: float) -> Point:
         """Gets point in deck coordinates based on percentage of the radius of each axis."""
         return self._geometry.from_center_cartesian(x, y, z)

api/src/opentrons/protocol_api/core/well.py

@@ -79,6 +79,10 @@ def load_liquid(
     ) -> None:
         """Load liquid into a well."""
 
+    @abstractmethod
+    def load_empty(self) -> None:
+        """Mark a well as containing no liquid."""
+
     @abstractmethod
     def from_center_cartesian(self, x: float, y: float, z: float) -> Point:
         """Gets point in deck coordinates based on percentage of the radius of each axis."""

api/src/opentrons/protocol_api/labware.py

@@ -280,12 +280,20 @@ def load_liquid(self, liquid: Liquid, volume: float) -> None:
 
         :param Liquid liquid: The liquid to load into the well.
         :param float volume: The volume of liquid to load, in µL.
+
+        .. note::
+            In API Version 2.22 and above, use `load_empty()` to mark a well as empty at the beginning of a protocol.
         """
         self._core.load_liquid(
             liquid=liquid,
             volume=volume,
         )
 
+    @requires_version(2, 22)
+    def load_empty(self) -> None:
+        """Mark a well as empty."""
+        self._core.load_empty()
+
     def _from_center_cartesian(self, x: float, y: float, z: float) -> Point:
         """
         Private version of from_center_cartesian. Present only for backward

api/tests/opentrons/protocol_api/test_well.py

@@ -8,6 +8,8 @@
 from opentrons.protocol_api._liquid import Liquid
 from opentrons.types import Point, Location
 
+from . import versions_at_or_above
+
 
 @pytest.fixture
 def mock_well_core(decoy: Decoy) -> WellCore:
@@ -140,6 +142,13 @@ def test_load_liquid(decoy: Decoy, mock_well_core: WellCore, subject: Well) -> N
     )
 
 
+@pytest.mark.parametrize("api_version", versions_at_or_above(APIVersion(2, 22)))
+def test_load_empty(decoy: Decoy, mock_well_core: WellCore, subject: Well) -> None:
+    """It should mark a location as empty."""
+    subject.load_empty()
+    decoy.verify(mock_well_core.load_empty(), times=1)
+
+
 def test_diameter(decoy: Decoy, mock_well_core: WellCore, subject: Well) -> None:
     """It should get the diameter from the core."""
     decoy.when(mock_well_core.diameter).then_return(12.3)