Add wall regen helper, fillet underside, bug sweep

Wall body rebuild + slab underside re-clip are now unified behind
tool.Model.regenerate_wall and called from split / merge / extend
operators. Fillet corner walls accept extend-to-underside (poll +
operator partition switched to is_path_connectable_wall) and surface
the wall-unjoin gizmo without the parametric-edit gate, since
fillets cannot enter that lifecycle. DumbWallJoiner.split strips the
duplicate's inherited slab-trim booleans up front so wall2 lands at
the cut point. regenerate_fillet_corner_wall re-clips after the body
rewrite so a prior extend-to-slab survives neighbour recalcs.

Drive-by bug sweep: tuple typo in hotkey_S_G's IfcSpace check,
defensive .get() in draw_regen_operations for partial AuthoringData
loads, and a try/except in get_active_representation matching the
existing convention for stale mesh ifc_definition_ids after a
representation rebuild.

Tests cover the regenerate_wall branching, the get_active_representation
stale-id contract, and the GizmoWallExtendVertically fillet acceptance.

Generated with the assistance of an AI coding tool.

src/bonsai/test/tool/test_geometry.py

@@ -135,6 +135,37 @@ class TestGetRepresentationData(NewFile):
         assert subject.get_representation_data(representation) == data
 
 
+class TestGetActiveRepresentation(NewFile):
+    def test_returns_representation_for_live_id(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        representation = ifc.createIfcShapeRepresentation()
+        mesh = bpy.data.meshes.new("Mesh")
+        obj = bpy.data.objects.new("Object", mesh)
+        tool.Geometry.get_mesh_props(mesh).ifc_definition_id = representation.id()
+        assert subject.get_active_representation(obj) == representation
+
+    def test_returns_none_when_mesh_has_no_id(self):
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        obj = bpy.data.objects.new("Object", bpy.data.meshes.new("Mesh"))
+        assert subject.get_active_representation(obj) is None
+
+    def test_returns_none_when_id_is_stale(self):
+        """A representation rebuild can free the old entity while obj.data
+        still tracks its id. Returning ``None`` keeps every UI redraw alive
+        instead of spamming ``RuntimeError`` from the by_id lookup."""
+        ifc = ifcopenshell.file()
+        tool.Ifc.set(ifc)
+        representation = ifc.createIfcShapeRepresentation()
+        mesh = bpy.data.meshes.new("Mesh")
+        obj = bpy.data.objects.new("Object", mesh)
+        stale_id = representation.id()
+        tool.Geometry.get_mesh_props(mesh).ifc_definition_id = stale_id
+        ifc.remove(representation)
+        assert subject.get_active_representation(obj) is None
+
+
 class TestGetRepresentationId(NewFile):
     def test_run(self):
         ifc = ifcopenshell.file()