Add external SVG reference support to manual drawing reference tags

Extends manual drawing reference annotations (elevation and section) to
also support external SVG references imported via bim.add_reference.

- Add "Is a Reference" checkbox to the annotation tool sidebar, shown
  when Elevation or Section is the active type; checking it and pressing
  Add opens a dialog to optionally link the tag to a Bonsai drawing or
  an external SVG reference
- The MANUAL_DRAWING_REFERENCE dropdown type is retained for backwards
  compatibility; selecting it shows a style picker (Elevation/Section)
  and the same linking dialog
- External-reference annotations are flagged with IsDocumentReference
  in EPset_Annotation and linked to their IfcDocumentInformation via
  IfcRelAssociatesDocument; drawing-reference annotations continue to
  use IfcRelAssignsToProduct as before
- SVG export resolves the correct reference/sheet IDs for both link
  types via get_reference_and_sheet_id_from_annotation
- Add IsDocumentReference to the EPset_Annotation pset template

src/bonsai/bonsai/bim/module/drawing/ui.py

@@ -559,8 +559,9 @@ class BIM_PT_product_assignments(Panel):
         element = tool.Ifc.get_entity(obj)
         if element and tool.Drawing.is_manual_drawing_reference(element):
             row = self.layout.row(align=True)
+            fallback = "No Reference Assigned" if element.ObjectType == "REFERENCE" else "No Drawing Assigned"
             row.label(
-                text=ProductAssignmentsData.data["relating_product"] or "No Drawing Assigned", icon="IMAGE_DATA"
+                text=ProductAssignmentsData.data["relating_product"] or fallback, icon="IMAGE_DATA"
             )
             row.operator("bim.assign_manual_drawing_reference", icon="GREASEPENCIL", text="")
             return

src/bonsai/bonsai/core/drawing.py

@@ -562,6 +562,14 @@ def assign_manual_drawing_reference(
         ifc.run("drawing.assign_product", relating_product=drawing, related_object=element)
 
 
+def assign_manual_reference_document(
+    drawing_tool: type[tool.Drawing],
+    element: ifcopenshell.entity_instance,
+    document: Optional[ifcopenshell.entity_instance],
+) -> None:
+    drawing_tool.set_annotation_reference_doc(element, document)
+
+
 def build_schedule(drawing: type[tool.Drawing], schedule: ifcopenshell.entity_instance) -> None:
     drawing.create_svg_schedule(schedule)
     drawing.open_svg(drawing.get_path_with_ext(drawing.get_document_uri(schedule), "svg"))

src/bonsai/bonsai/tool/drawing.py

@@ -2021,6 +2021,49 @@ class Drawing(bonsai.core.tool.Drawing):
             pset = ifcopenshell.api.pset.add_pset(ifc_file, product=element, name="EPset_Annotation")
         ifcopenshell.api.pset.edit_pset(ifc_file, pset=pset, properties={"IsManualDrawingReference": True})
 
+    @classmethod
+    def is_document_reference(cls, element: ifcopenshell.entity_instance) -> bool:
+        """Return True if this annotation links to an external document (not a Bonsai drawing camera)."""
+        return bool(ifcopenshell.util.element.get_pset(element, "EPset_Annotation", "IsDocumentReference"))
+
+    @classmethod
+    def set_document_reference_flag(cls, element: ifcopenshell.entity_instance) -> None:
+        """Mark this annotation as pointing to an external document reference."""
+        ifc_file = tool.Ifc.get()
+        pset = tool.Pset.get_element_pset(element, "EPset_Annotation")
+        if not pset:
+            pset = ifcopenshell.api.pset.add_pset(ifc_file, product=element, name="EPset_Annotation")
+        ifcopenshell.api.pset.edit_pset(ifc_file, pset=pset, properties={"IsDocumentReference": True})
+
+    @classmethod
+    def get_annotation_reference_doc(
+        cls, element: ifcopenshell.entity_instance
+    ) -> Union[ifcopenshell.entity_instance, None]:
+        """Return the IfcDocumentInformation linked to a document-reference annotation."""
+        for rel in element.HasAssociations:
+            if rel.is_a("IfcRelAssociatesDocument"):
+                doc = rel.RelatingDocument
+                if doc.is_a("IfcDocumentInformation"):
+                    return doc
+        return None
+
+    @classmethod
+    def set_annotation_reference_doc(
+        cls,
+        element: ifcopenshell.entity_instance,
+        document: Union[ifcopenshell.entity_instance, None],
+    ) -> None:
+        """Associate (or clear) an IfcDocumentInformation on a document-reference annotation."""
+        ifc_file = tool.Ifc.get()
+        # Remove existing document associations on this annotation.
+        for rel in list(element.HasAssociations):
+            if rel.is_a("IfcRelAssociatesDocument"):
+                ifcopenshell.api.document.unassign_document(
+                    ifc_file, products=[element], document=rel.RelatingDocument
+                )
+        if document:
+            ifcopenshell.api.document.assign_document(ifc_file, products=[element], document=document)
+
     @classmethod
     def regenerate_elevation_reference_annotation(
         cls,