Bonsai: Representation Items panel crashes with "Instance #N not found" after a .blend/.ifc round trip #9447

Bug Description

The Representation Items panel stores its item list in the .blend, but never checks that the ids are still valid against the loaded IFC. After a .blend/.ifc round trip (open the .blend, which reloads the .ifc next to it) the list can be replayed against a different state of the file, and the first button that touches an item raises:

Python: Traceback (most recent call last):
  File "...\bonsai\tool\ifc.py", line 367, in execute
    IfcStore.execute_ifc_operator(self, context)
  File "...\bonsai\bim\ifc.py", line 569, in execute_ifc_operator
    result = getattr(operator, "_execute")(context)
  File "...\bonsai\bim\module\geometry\operator.py", line 3586, in _execute
    representation_item = ifc_file.by_id(representation_item_id)
  File "...\ifcopenshell\file.py", line 836, in by_id
    return self[id]
  File "...\ifcopenshell\file.py", line 823, in __getitem__
    return entity_instance(self.wrapped_data.by_id(key), self)
  File "...\ifcopenshell\ifcopenshell_wrapper.py", line 5826, in by_id
    return _ifcopenshell_wrapper.file_by_id(self, id)
RuntimeError: Instance #1937489 not found

Opening the same .ifc directly (no .blend) does not produce the error - the list is then rebuilt from the file that was just loaded, so every id resolves.

Cause

BIMObjectGeometryProperties.items is a CollectionProperty on the object (bim/module/geometry/prop.py), so is_editing and every items[].ifc_definition_id are written into the .blend. EnableEditingRepresentationItems is the only thing that rebuilds them. Nothing invalidates that list when the IFC is (re)loaded, so a list captured in one session can outlive the instances it points at, and the operators then call by_id() on a dead id with no guard.

Affected call sites

All on v0.9.0 (checked at e18d927), src/bonsai/bonsai/bim/module/geometry/operator.py:

UnassignRepresentationItemStyle already resolves through tool.Ifc.get_entity_by_id and reports instead of raising, but it leaves the stale list in place, so the next click fails the same way.

Suggested fix

Route these through the existing None-returning accessor tool.Ifc.get_entity_by_id in a small helper that, on a dead id, reports the error and rebuilds the list with the disable_editing_representation_items / enable_editing_representation_items pair that these operators already use as "reload items ui". The panel then heals itself: the user gets a message instead of a traceback, a list matching the loaded IFC, and the click works on the retry.

That is a lazy fix at the point of use. The underlying condition - per-object representation-item editing state surviving an IFC load - is still there, and the fuller cure would be to reset is_editing/items on every object when a project loads. Happy to open a PR for the guards if that direction is agreeable.

Related

• Instance #304 not found #6942 - same class of bug (stale Blender-side IFC id after saving .blend + .ifc together), but in tool.Geometry.get_active_representation reading the mesh props rather than the items list. Closed as stale in Sept 2025 without a fix; would still crash after the guards above.
• Bonsai: sync Representation Items list selection with the 3D viewport #8924 (open) is the only open PR working on this list - it syncs active_item_index with the viewport but does not validate the ids, so it inherits the same crash.

Environment

os: Windows 10 (10.0.19045)
blender_version: 5.2
python_version: 3.13
bonsai: local build off v0.8.0; the affected code is identical on v0.9.0 @ e18d927b40