fix(hamilton): resolve trash_core96 from the deck instead of a stale pointer

pylabrobot/resources/hamilton/hamilton_deck_tests.py

@@ -1,7 +1,7 @@
 import textwrap
 import unittest
 
-from pylabrobot.resources import TipRack
+from pylabrobot.resources import Deck, TipRack
 from pylabrobot.resources.corning import (
   cor_96_wellplate_360uL_Fb,
 )
@@ -94,6 +94,30 @@ def test_teaching_rack_excluded_by_nominal_volume_search(self):
     self.assertEqual(len(matches), 5)
     self.assertNotIn("teaching_tip_rack", {tr.name for tr in matches})
 
+  def test_get_trash_area96_survives_serialization_round_trip(self):
+    """`serialize()` encodes the 96 trash as a child and sets `with_trash96=False`, so the
+    rebuilt deck never runs the `with_trash96` branch in `__init__`. `get_trash_area96()` must
+    still resolve it from the child tree rather than raising."""
+    deck = self.build_layout()
+    original_location = deck.get_trash_area96().get_location_wrt(deck)
+
+    deck2 = Deck.deserialize(deck.serialize())
+
+    self.assertIn("trash_core96", [child.name for child in deck2.children])
+    self.assertEqual(deck2.get_trash_area96().get_location_wrt(deck2), original_location)
+
+  def test_get_trash_area96_raises_after_clear_include_trash(self):
+    """`clear(include_trash=True)` unassigns the 96 trash, so `get_trash_area96()` must raise
+    rather than hand back the now-orphaned resource."""
+    deck = self.build_layout()
+    deck.get_trash_area96()  # resolves while still assigned
+
+    deck.clear(include_trash=True)
+
+    self.assertNotIn("trash_core96", [child.name for child in deck.children])
+    with self.assertRaises(RuntimeError):
+      deck.get_trash_area96()
+
   def test_assign_gigantic_resource(self):
     stanley_cup = StanleyCup_QUENCHER_FLOWSTATE_TUMBLER(name="HUGE")
     deck = STARLetDeck()

pylabrobot/resources/hamilton/hamilton_decks.py

@@ -458,12 +458,11 @@ def __init__(
       origin=origin,
     )
 
-    self._trash96: Optional[Trash] = None
     if with_trash96:
       # got this location from a .lay file, but will probably need to be adjusted by the user.
-      self._trash96 = Trash("trash_core96", size_x=122.4, size_y=82.6, size_z=0)  # size of tiprack
+      trash96 = Trash("trash_core96", size_x=122.4, size_y=82.6, size_z=0)  # size of tiprack
       self.assign_child_resource(
-        resource=self._trash96,
+        resource=trash96,
         location=Coordinate(x=-42.0 - 16.2, y=120.3 - 14.3, z=216.4),
       )
 
@@ -548,11 +547,11 @@ def rails_to_location(self, rails: int) -> Coordinate:
     return Coordinate(x=x, y=63, z=100)
 
   def get_trash_area96(self) -> Trash:
-    if self._trash96 is None:
+    if not self.has_resource("trash_core96"):
       raise RuntimeError(
         "Trash area for 96-well plates was not created. Initialize with `with_trash96=True`."
       )
-    return self._trash96
+    return cast(Trash, self.get_resource("trash_core96"))
 
   def clear(self, include_trash: bool = False):
     """Clear the deck, removing all resources except the trash areas and the waste block."""