Update opening-template dev-note

Reflect void-propagation-to-all-occurrences and adjusted-extrusion
preservation added to #8200 since the note was seeded.

Generated with the assistance of an AI coding tool.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

AGENTS.md

@@ -129,6 +129,21 @@ on CI to catch formatting issues.
   within each package under `src/`.
 - Run the existing test suite for the package you modified before submitting.
 
+## In-Progress Feature Notes
+
+Living design and working notes for unmerged feature branches live in
+[`docs/dev-notes/`](docs/dev-notes/), one Markdown file per feature, named after the
+branch. They capture the problem, the design decisions and the *why*, and what still
+needs testing — so collaborators (and their AI agents) can pick up the context behind a
+branch. Because the note is committed on the branch, it travels with the PR.
+
+- Before working on a feature branch, read its note in `docs/dev-notes/` if one exists.
+- Keep the note current as the PR is refined.
+- These are not user documentation; at merge they are removed or their durable parts
+  promoted to code comments / permanent docs.
+
+See [`docs/dev-notes/README.md`](docs/dev-notes/README.md) for details.
+
 ## Architecture Quick Reference
 
 ### Directory Structure

docs/dev-notes/README.md

@@ -0,0 +1,28 @@
+<!-- This file was generated with the assistance of an AI coding tool. -->
+
+# Developer notes (in-progress features)
+
+This directory holds **living design/working notes for unmerged feature branches**,
+one Markdown file per feature, named after its branch (e.g.
+`opening-template-on-type.md`).
+
+## Purpose
+
+A shared scratchpad so collaborators — and the AI agents they work with — can pick up
+the context behind an in-progress branch: the problem, the design decisions and the
+*why*, dead ends already ruled out, and what still needs testing. Because the note is
+committed on the branch, it travels with the PR and shows up in the diff, so it is
+discoverable without anyone being told where to look.
+
+## How to use it (humans and agents)
+
+- **Before working on a feature branch**, read its note here if one exists.
+- **As the PR is refined**, keep the note current — append decisions, correct things
+  that changed, update the test checklist.
+- **One file per feature**, named after the branch.
+
+## Lifecycle
+
+These are *not* permanent user documentation. When a PR merges, either remove its note
+or promote the durable parts (the load-bearing "why") into code comments or the regular
+docs, so stale notes do not accumulate on the default branch.

docs/dev-notes/opening-template-on-type.md

@@ -0,0 +1,165 @@
+<!-- This file was generated with the assistance of an AI coding tool. -->
+
+# Opening template on type — preserving custom openings across duplicate_type / append
+
+> **Living dev note** for the `opening-template-on-type` branch/PR. Read before working
+> on the feature; append decisions and findings as the PR is refined. This is *not* user
+> documentation — at merge it is removed or its durable parts promoted to code comments.
+> See [README.md](README.md) for the convention.
+
+## Problem
+
+`bpy.ops.bim.duplicate_type` and `bpy.ops.bim.append_library_element` lose a custom
+`IfcOpeningElement` body (e.g. an `IfcPolygonalFaceSet`/tessellation) and replace it
+with a generated extrusion. Root cause: the only mechanism that preserved a custom
+opening was "copy it from a sibling occurrence of the same type"
+(`get_existing_opening_occurrence_if_any`), which returns nothing for a brand-new
+type. `generate_opening_from_filling` then always builds an extrusion (profile or
+bbox), discarding the custom geometry.
+
+## Key facts established
+
+- IFC-level `root.copy_class` already `copy_deep`s opening representations; the loss
+  happens on the Bonsai side (the `regenerate_from_type` listener on
+  `type.assign_type`, and placement-time generation).
+- Opening occurrences of one type already **share** a single `IfcRepresentationMap`
+  via mapped representations — that is why editing one void edits them all
+  (see `tool.Model.unshare_opening_representation` docstring). Bonsai shares, it does
+  not copy. The shared map just has no durable home (it is hosted implicitly by
+  whichever occurrence exists), so it does not survive to a new type.
+- IFC4 ADD2 TC1 `IfcShapeRepresentation`: identifier **`Reference`** = "3D
+  representation that is **not part of the Body representation** ... used, e.g., for
+  opening geometries ... excluded from an implicit Boolean operation." Schema-valid;
+  `IfcTypeProduct` has no uniqueness rule on `RepresentationMaps` (only
+  `ApplicableOccurrence`). So a `Reference` map can sit beside the `Body` map.
+- The geometry kernel selects an opening's geometry **by context, not by
+  `RepresentationIdentifier`** (`mapping::representation_of`, `ifcgeom/mapping/mapping.cpp`).
+  So a `Reference`-identified opening in the Body context still booleans correctly.
+  Nothing in Bonsai reads `"Reference"` to *skip* applying an opening.
+- Caveat: IFC has no type-level void (`IfcRelVoidsElement` is occurrence-only). The
+  "opening template on type" is therefore a Bonsai convention using a spec-valid
+  identifier; other tools see a harmless extra `Reference` rep they ignore. The
+  regeneration smarts are Bonsai-only by necessity.
+
+## Design
+
+Store the shared opening body on the **type** as a `Reference` representation map.
+Because `bim.duplicate_type` (`tool.Root.copy_representation`) and
+`append_type_product` both copy a type's `RepresentationMaps`, the template survives
+both. Occurrence openings map over the same map, so editing a void rewrites the
+shared map = updates the type template in one stroke (no separate write-back needed).
+
+`map_type_representations` must skip `Reference` maps so the window/door occurrence
+does not receive the opening shape as its own Body (the kernel would otherwise pick
+arbitrarily between the real Body and the opening rep). The skip is both required and
+spec-endorsed ("not part of the Body representation").
+
+### Body-context coexistence (Option A)
+
+The template lives in the **Body** subcontext (required: the instance opening that maps
+over it must resolve in Body context for the geometry kernel to subtract it). So the
+type holds two reps in one context: the `Body` window body and the `Reference` opening
+template. Per IFC, `Reference` is a *RepresentationIdentifier value used within the Body
+context*, not a separate context - so we keep it there and disambiguate elsewhere:
+
+- The representations panel now shows `RepresentationIdentifier` as its own column
+  (`geometry/data.py`, `geometry/ui.py`) so the two Body-context reps are
+  distinguishable (`Model | Body | MODEL_VIEW | Reference | Tessellation`). The panel
+  column previously read "Body" because it shows `ContextOfItems.ContextIdentifier`,
+  not the representation's identifier.
+- `Geometry.reimport_element_representations` type branch now renders the requested
+  `base_representation` instead of `get_representation(element, context)`, which matched
+  only by context and returned the window body when switching to the `Reference` rep.
+  This is what makes "switch to the Reference row" actually show the void on the type.
+
+### Precedence in `generate_opening_from_filling`
+type `Reference` template → (existing sibling occurrence, checked by callers) →
+type `Profile` extrusion → bbox extrusion.
+
+### Type switching (assign_type)
+
+On `type.assign_type` the opening is rebuilt to reflect the **assigned** type's void.
+Two listeners in `model/handler.py`:
+
+- **pre** `Bonsai.Opening.PreserveOnTypeChange` → `preserve_opening_on_type_change`:
+  before the filling moves to the new type, `promote_opening_to_type(old_type)` anchors
+  the old type's custom void as a template, so it isn't lost when (possibly the last)
+  occurrence is regenerated. Idempotent; custom voids only.
+- **post** `Bonsai.Opening.RegenerateFromType` → `regenerate_from_type` →
+  `_regenerate_from_type`: rebuilds from the new type's template / sibling / extrusion.
+  The old PR1 "preserve custom" guard was **removed** here — it kept the previous type's
+  void on a switch (wrong), and the template now makes preservation unnecessary.
+
+NOTE: upstream `v0.8.0` landed `assign_type` changes + new `test_assign_type_*` tests
+(merged under this branch's base). The listeners ride on top of that — re-test the
+switch/edit round-trips against the new `assign_type`.
+
+### Write-back on void edit
+
+Editing an occurrence's void writes the new geometry back to the type's `Reference`
+template via `update_type_template_from_opening` (creates the template if absent), then
+**re-maps every occurrence's opening onto the template** and reloads the affected host walls
+(`switch_representation`) so they re-boolean. The re-map (`_remap_opening_to_template`) is the
+key part: an earlier version only re-pointed a *pre-existing* shared map, so siblings whose
+openings were **independent** (their own `IfcRepresentationMap`, never sharing the template)
+didn't follow — the common real-world case. Now they do. Hooked at both commit paths:
+`UpdateRepresentation._execute` (the `edited_objs` path) and
+`OverrideModeSetObject` after `edit_representation_item` (the in-place item edit). The
+older `edit_openings`/`is_edited` path also calls it. `set_type_opening_representation`
+has replace semantics (one `Reference` map per type).
+
+### Preserving adjusted extrusions (duplicate_type)
+
+`is_opening_representation_custom` only flags *non-extrusion* geometry (tessellation, brep,
+CSG) as worth preserving — a proxy for "not regenerable". That mis-classifies a *manually
+adjusted* extrusion, which is still an `IfcExtrudedAreaSolid`, so a hand-tweaked extrusion
+opening was reset to the default on `duplicate_type`.
+
+`promote_opening_to_type` now gates on `should_preserve_opening` = custom **or**
+`_is_adjusted_extrusion`. The latter generates the default (`generate_opening_from_filling`,
+which yields the default since no template exists at promote time) *transiently*, compares the
+two bodies' axis-aligned bounding boxes (1 mm tolerance) via the geom engine, then removes the
+temporary default. Divergence ⇒ the extrusion was adjusted ⇒ promote it; a plain default
+matches ⇒ left regenerable (not frozen — see the "freeze" discussion). Scoped to the duplicate
+path so the generate-and-compare stays out of the hot predicate. Limitation: bbox comparison
+misses a shape change that preserves the bbox (upgrade to a vertex-set compare if needed).
+
+## Status — implemented (manually verified in Blender)
+
+- core `map_type_representations.py`: skip `Reference` maps.
+- `model/opening.py`: `get_/set_type_opening_representation`, `promote_opening_to_type`,
+  `update_type_template_from_opening` (+ `_remap_opening_to_template`),
+  `preserve_opening_on_type_change`, `should_preserve_opening` (+ `_is_adjusted_extrusion`,
+  `_representation_bbox`); `generate_opening_from_filling` consults the template; PR1 guard
+  removed from `_regenerate_from_type`.
+- `model/handler.py`: pre + post assign_type listeners.
+- `type/operator.py` `DuplicateType`: promote before copy.
+- `project/operator.py` `AppendLibraryElement`: `harvest_opening_template`.
+- `geometry/operator.py`: write-back hooks in `UpdateRepresentation` and
+  `OverrideModeSetObject`; `reimport_element_representations` renders the requested rep.
+- `geometry/data.py` + `geometry/ui.py`: `RepresentationIdentifier` column + headers.
+
+Branch `opening-template-on-type` (#8200): initial feature commit + the #7916 build-conflict
+ancestry-merge + void-propagation-to-all-occurrences + adjusted-extrusion preservation. The
+`docs/dev-notes/` convention itself lives on the stacked branch `dev-notes-system` (#8201).
+
+Still **deferred:** explicit "Apply/Reset to type" operators + a "diverges from type"
+indicator; import never auto-writes back. `update_simple_openings` still keeps its
+`is_opening_representation_custom` guard (array propagation, same type — left as-is).
+
+## Things to test / verify
+
+- Duplicated/appended type's new occurrence gets the faceset void and it **cuts** the
+  wall (kernel selects opening geom by context, so a `Reference`-id rep still booleans).
+- `harvest_opening_template` cross-file `file.add`: no duplicate
+  `IfcGeometricRepresentationContext` left behind; units (kernel doesn't rescale rep
+  coords — same assumption as `append_asset`).
+- Switch X→Y→X round-trip restores each type's void; switching to a plain (template-less)
+  type gives its default extrusion, not the previous faceset.
+- Edit a void → type's `Reference` row updates; **all** occurrences follow (including ones
+  that had independent openings) and their host walls re-boolean; survives duplicate.
+- `duplicate_type` on a type whose extrusion opening was **manually adjusted** → Type B keeps
+  the adjusted extrusion; a type with a plain/default extrusion stays regenerable (not frozen).
+- Three write-back hooks are intentional (different commit paths) — candidate for
+  consolidation in review.
+- Re-test against upstream's new `assign_type` (see NOTE under "Type switching").

src/bonsai/bonsai/bim/module/geometry/__init__.py

@@ -69,6 +69,7 @@ classes = (
     operator.RemoveRepresentation,
     operator.RemoveRepresentationItem,
     operator.RemoveRepresentationItemFromShapeAspect,
+    operator.SelectByRepresentationType,
     operator.SelectConnection,
     operator.SelectRepresentationItem,
     operator.SwitchRepresentation,

src/bonsai/bonsai/bim/module/geometry/data.py

@@ -138,6 +138,11 @@ class RepresentationsData:
                 "ContextType": representation.ContextOfItems.ContextType or "",
                 "ContextIdentifier": "",
                 "TargetView": "",
+                # The representation's own identifier (e.g. 'Body', 'Reference'), which is
+                # distinct from the subcontext's ContextIdentifier above. Two reps can share
+                # one context (e.g. a Body body and a Reference opening template), so showing
+                # this lets them be told apart in the panel.
+                "RepresentationIdentifier": representation.RepresentationIdentifier or "",
                 "RepresentationType": representation_type or "",
                 "is_active": is_active,
             }

src/bonsai/bonsai/bim/module/geometry/operator.py

@@ -418,6 +418,55 @@ class SelectConnection(bpy.types.Operator, tool.Ifc.Operator):
         core.select_connection(tool.Geometry, connection=tool.Ifc.get().by_id(self.connection))
 
 
+class SelectByRepresentationType(bpy.types.Operator):
+    bl_idname = "bim.select_by_representation_type"
+    bl_label = "Select By Representation Type"
+    bl_description = (
+        "Select objects whose active representation matches this type. "
+        "Ctrl+Click to also include objects that have this type in any representation (active or not)"
+    )
+    bl_options = {"REGISTER", "UNDO"}
+    representation_type: bpy.props.StringProperty()
+    select_inactive: bpy.props.BoolProperty(default=False, options={"SKIP_SAVE"})
+
+    def invoke(self, context, event):
+        self.select_inactive = event.ctrl
+        return self.execute(context)
+
+    def execute(self, context):
+        ifc = tool.Ifc.get()
+        if not ifc:
+            return {"CANCELLED"}
+        # Strip the "*" suffix used for mapped/resolved representations.
+        target_type = self.representation_type.rstrip("*")
+        matched = 0
+        for obj in context.visible_objects:
+            element = tool.Ifc.get_entity(obj)
+            if not element:
+                obj.select_set(False)
+                continue
+            if self.select_inactive:
+                # Ctrl: match any representation on the element, active or not.
+                has_type = any(
+                    (ifcopenshell.util.representation.resolve_representation(rep).RepresentationType or "") == target_type
+                    for rep in ifcopenshell.util.representation.get_representations_iter(element)
+                )
+            else:
+                # Default: match only the currently active (displayed) representation.
+                active_rep = tool.Geometry.get_active_representation(obj)
+                if active_rep is None:
+                    obj.select_set(False)
+                    continue
+                resolved = ifcopenshell.util.representation.resolve_representation(active_rep)
+                has_type = (resolved.RepresentationType or "") == target_type
+            obj.select_set(has_type)
+            if has_type:
+                matched += 1
+        mode = "any representation" if self.select_inactive else "active representation"
+        self.report({"INFO"}, f"Selected {matched} object(s) with RepresentationType '{target_type}' ({mode})")
+        return {"FINISHED"}
+
+
 class RemoveConnection(bpy.types.Operator, tool.Ifc.Operator):
     bl_idname = "bim.remove_connection"
     bl_label = "Remove Connection"
@@ -710,6 +759,16 @@ class UpdateRepresentation(bpy.types.Operator, tool.Ifc.Operator):
         if mprops.ifc_parameters:
             core.get_representation_ifc_parameters(tool.Geometry, obj=obj)
 
+        # Persist an edited opening void onto its filling type's 'Reference' template so the
+        # change survives type duplication/append/switching and propagates to siblings. This
+        # catches the edited_objs commit path; the in-place item edit is caught in
+        # bim.override_mode_set_object.
+        edited_element = tool.Ifc.get_entity(obj)
+        if edited_element and edited_element.is_a("IfcOpeningElement"):
+            from bonsai.bim.module.model.opening import FilledOpeningGenerator
+
+            FilledOpeningGenerator().update_type_template_from_opening(edited_element)
+
 
 class UpdateParametricRepresentation(bpy.types.Operator):
     bl_idname = "bim.update_parametric_representation"
@@ -2489,6 +2548,15 @@ class OverrideModeSetObject(bpy.types.Operator, tool.Ifc.Operator):
                 return bpy.ops.bim.edit_boundary_geometry()
             elif tool.Geometry.is_representation_item(context.active_object):
                 self.edit_representation_item(context.active_object)
+                # If we just edited an opening's void item, persist the new shape onto the
+                # filling type's 'Reference' template so it survives type duplication/append/
+                # switching and propagates to siblings.
+                rep_obj = tool.Geometry.get_geometry_props().representation_obj
+                edited_element = tool.Ifc.get_entity(rep_obj) if rep_obj else None
+                if edited_element and edited_element.is_a("IfcOpeningElement"):
+                    from bonsai.bim.module.model.opening import FilledOpeningGenerator
+
+                    FilledOpeningGenerator().update_type_template_from_opening(edited_element)
                 tool.Root.reload_item_decorator()
                 # So you can keep hitting tab to cycle out of edit mode
                 context.active_object.select_set(False)

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

@@ -148,12 +148,29 @@ class BIM_PT_representations(Panel):
             self.layout.label(text="No Representations Found")
             return
 
+        header = self.layout.row(align=True)
+        header.label(text="Context")
+        header.label(text="Subcontext")
+        header.label(text="View")
+        header.label(text="Identifier")
+        header.label(text="Type")
+        # Blank icon cells reserve the same width as the switch/remove buttons below so the
+        # text columns line up with the data rows.
+        header.label(text="", icon="BLANK1")
+        header.label(text="", icon="BLANK1")
+
         for representation in RepresentationsData.data["representations"]:
             row = self.layout.row(align=True)
             row.label(text=representation["ContextType"])
             row.label(text=representation["ContextIdentifier"])
             row.label(text=representation["TargetView"])
-            row.label(text=representation["RepresentationType"])
+            row.label(text=representation["RepresentationIdentifier"])
+            op = row.operator(
+                "bim.select_by_representation_type",
+                text=representation["RepresentationType"],
+                emboss=False,
+            )
+            op.representation_type = representation["RepresentationType"]
             op = row.operator(
                 "bim.switch_representation",
                 icon="FILE_REFRESH" if representation["is_active"] else "OUTLINER_DATA_MESH",

src/bonsai/bonsai/bim/module/model/handler.py

@@ -41,6 +41,12 @@ def load_post(*args):
         profile.DumbProfileRegenerator().regenerate_from_profile,
     )
 
+    ifcopenshell.api.add_pre_listener(
+        "type.assign_type",
+        "Bonsai.Opening.PreserveOnTypeChange",
+        opening.FilledOpeningGenerator().preserve_opening_on_type_change,
+    )
+
     ifcopenshell.api.add_post_listener(
         "type.assign_type",
         "Bonsai.Opening.RegenerateFromType",

src/bonsai/bonsai/bim/module/model/opening.py

@@ -420,6 +420,25 @@ class FilledOpeningGenerator:
 
                 tool.Geometry.recut_host(voided_obj, representation)
 
+    def preserve_opening_on_type_change(
+        self, usecase_path: str, ifc_file: ifcopenshell.file, settings: dict[str, Any]
+    ) -> None:
+        """Pre-listener for type.assign_type: anchor the old type's void before reassigning.
+
+        A custom void that lives only on an occurrence (the type has no 'Reference'
+        template) would be lost when that occurrence is moved to another type - the
+        post-assign regeneration replaces it. Promoting it onto its current type first
+        keeps it durable, so switching back later restores it. Idempotent and only acts on
+        genuinely custom (non-extrusion) voids.
+        """
+        relating_type = settings.get("relating_type")
+        for related_object in settings.get("related_objects") or []:
+            if not getattr(related_object, "FillsVoids", None):
+                continue
+            old_type = ifcopenshell.util.element.get_type(related_object)
+            if old_type and old_type != relating_type:
+                self.promote_opening_to_type(old_type)
+
     def regenerate_from_type(self, usecase_path: str, ifc_file: ifcopenshell.file, settings: dict[str, Any]) -> None:
         relating_type = settings["relating_type"]
 
@@ -437,6 +456,13 @@ class FilledOpeningGenerator:
         opening = filling.FillsVoids[0].RelatingOpeningElement
         voided_element = opening.VoidsElements[0].RelatingBuildingElement
 
+        # Always regenerate the opening to reflect the *assigned* type's void: its
+        # 'Reference' template if it has one (generate_opening_from_filling consults it),
+        # else a sibling occurrence's opening, else a generated extrusion. We deliberately
+        # do NOT preserve the previous type's custom void on a type change - a custom void
+        # now survives duplicate_type/append by being anchored on the type as a template
+        # (promote_opening_to_type / harvest), so keeping the old void here would just show
+        # the wrong type's opening (e.g. switching to a plain type would keep the faceset).
         opening_rep = ifcopenshell.util.representation.get_representation(opening, "Model", "Body", "MODEL_VIEW")
         ifcopenshell.api.geometry.unassign_representation(tool.Ifc.get(), product=opening, representation=opening_rep)
         ifcopenshell.api.geometry.remove_representation(tool.Ifc.get(), representation=opening_rep)
@@ -493,6 +519,14 @@ class FilledOpeningGenerator:
         profile = None
         filling_type = ifcopenshell.util.element.get_type(filling)
         if filling_type:
+            # A stored opening template (e.g. a custom IfcPolygonalFaceSet carried
+            # across bim.duplicate_type / append) takes priority over generating a
+            # default extrusion. Returning the shared template representation lets the
+            # caller's map_representation reuse its IfcRepresentationMap, so this
+            # opening stays in sync with the type template and its sibling occurrences.
+            opening_template = self.get_type_opening_representation(filling_type)
+            if opening_template is not None:
+                return opening_template
             profile = ifcopenshell.util.representation.get_representation(
                 filling_type, "Model", "Profile", "ELEVATION_VIEW"
             )
@@ -590,6 +624,228 @@ class FilledOpeningGenerator:
                 return True
         return False
 
+    def is_opening_representation_custom(self, opening: ifcopenshell.entity_instance) -> bool:
+        """Whether the opening's Body has user-authored geometry rather than a generated extrusion.
+
+        Openings produced by ``generate_opening_from_filling`` always consist of a
+        single ``IfcExtrudedAreaSolid``. Anything else (a tessellation such as an
+        ``IfcPolygonalFaceSet``, a brep, a CSG solid, etc.) was authored by the user
+        and must not be silently replaced with a default extrusion.
+        """
+        representation = ifcopenshell.util.representation.get_representation(opening, "Model", "Body", "MODEL_VIEW")
+        if not representation:
+            return False
+        representation = ifcopenshell.util.representation.resolve_representation(representation)
+        return any(not item.is_a("IfcExtrudedAreaSolid") for item in representation.Items)
+
+    def should_preserve_opening(self, opening: ifcopenshell.entity_instance) -> bool:
+        """Whether an opening's geometry is worth anchoring on the type as a template.
+
+        True for user-authored geometry (a tessellation, brep, etc.) or a *manually adjusted*
+        extrusion - one that no longer matches the default ``generate_opening_from_filling``
+        would produce for its filling. A plain generated extrusion is regenerable, so it
+        returns False and is left to regenerate.
+        """
+        if self.is_opening_representation_custom(opening):
+            return True
+        return self._is_adjusted_extrusion(opening)
+
+    def _is_adjusted_extrusion(self, opening: ifcopenshell.entity_instance) -> bool:
+        """Whether the opening's extrusion diverges from the default for its filling.
+
+        Generates the default transiently, compares the axis-aligned bounding boxes of the
+        two bodies (both in the opening's local frame), then removes the temporary default.
+        A conservative False is returned when the default cannot be computed.
+        """
+        filling = opening.HasFillings[0].RelatedBuildingElement if getattr(opening, "HasFillings", None) else None
+        filling_obj = tool.Ifc.get_object(filling) if filling else None
+        current = ifcopenshell.util.representation.get_representation(opening, "Model", "Body", "MODEL_VIEW")
+        if not filling_obj or current is None:
+            return False
+        current = ifcopenshell.util.representation.resolve_representation(current)
+        default_representation = self.generate_opening_from_filling(filling, filling_obj)
+        try:
+            settings = ifcopenshell.geom.settings()
+            current_bbox = self._representation_bbox(settings, current)
+            default_bbox = self._representation_bbox(settings, default_representation)
+        finally:
+            ifcopenshell.api.geometry.remove_representation(tool.Ifc.get(), representation=default_representation)
+        if current_bbox is None or default_bbox is None:
+            return False
+        (cur_min, cur_max), (def_min, def_max) = current_bbox, default_bbox
+        tolerance = 1e-3  # 1 mm; differing extents/position => manually adjusted
+        return bool(np.any(np.abs(cur_min - def_min) > tolerance) or np.any(np.abs(cur_max - def_max) > tolerance))
+
+    @staticmethod
+    def _representation_bbox(settings: Any, representation: ifcopenshell.entity_instance):
+        try:
+            geometry = ifcopenshell.geom.create_shape(settings, representation)
+        except Exception:
+            return None
+        verts = ifcopenshell.util.shape.get_vertices(geometry)
+        if len(verts) == 0:
+            return None
+        return verts.min(axis=0), verts.max(axis=0)
+
+    def get_type_opening_representation(
+        self, filling_type: ifcopenshell.entity_instance
+    ) -> Union[ifcopenshell.entity_instance, None]:
+        """Return the type's stored opening template (its 'Reference' representation), if any.
+
+        The template is the shared opening body anchored on the type as a
+        'Reference'-identified representation map (see
+        :meth:`set_type_opening_representation`). Storing it on the type lets a
+        custom opening survive ``bim.duplicate_type`` and project append, which copy
+        the type's ``RepresentationMaps`` but not an opening shared only between
+        occurrences.
+        """
+        for representation_map in filling_type.RepresentationMaps or []:
+            representation = representation_map.MappedRepresentation
+            if representation.RepresentationIdentifier == "Reference":
+                return representation
+
+    def set_type_opening_representation(
+        self, filling_type: ifcopenshell.entity_instance, representation: ifcopenshell.entity_instance
+    ) -> None:
+        """Anchor an opening body representation on the type as its 'Reference' template.
+
+        ``representation`` is tagged 'Reference' (so it is excluded from the
+        occurrence body geometry, see
+        ``ifcopenshell.api.type.map_type_representations``) and the
+        ``IfcRepresentationMap`` wrapping it is registered in the type's
+        ``RepresentationMaps``, replacing any previous 'Reference' map. The existing map
+        is reused when present so that occurrences mapping over it stay in sync with the
+        type template. Idempotent.
+        """
+        ifc_file = tool.Ifc.get()
+        representation.RepresentationIdentifier = "Reference"
+        representation_map = next(
+            (i for i in ifc_file.get_inverse(representation) if i.is_a("IfcRepresentationMap")), None
+        )
+        if representation_map is None:
+            mapping_origin = ifc_file.createIfcAxis2Placement3D(
+                ifc_file.createIfcCartesianPoint((0.0, 0.0, 0.0)),
+                ifc_file.createIfcDirection((0.0, 0.0, 1.0)),
+                ifc_file.createIfcDirection((1.0, 0.0, 0.0)),
+            )
+            representation_map = ifc_file.createIfcRepresentationMap(mapping_origin, representation)
+        # Keep all non-'Reference' maps (Body, Annotation, ...) plus this one, dropping any
+        # previous 'Reference' template so the type carries exactly one.
+        new_maps = [
+            m
+            for m in (filling_type.RepresentationMaps or [])
+            if m == representation_map or m.MappedRepresentation.RepresentationIdentifier != "Reference"
+        ]
+        if representation_map not in new_maps:
+            new_maps.append(representation_map)
+        filling_type.RepresentationMaps = new_maps
+
+    def update_type_template_from_opening(self, opening: ifcopenshell.entity_instance) -> None:
+        """Write an edited opening's geometry back to its filling type's 'Reference' template.
+
+        After a user edits an opening's void shape, anchor the new geometry on the type so
+        the change is durable (survives duplicate_type/append and switching the type away
+        and back) and propagates to sibling occurrences. Only acts on custom (non-extrusion)
+        geometry; a re-generated extrusion needs no template.
+        """
+        if not getattr(opening, "HasFillings", None) or not self.is_opening_representation_custom(opening):
+            return
+        ifc_file = tool.Ifc.get()
+        new_representation = ifcopenshell.util.representation.get_representation(opening, "Model", "Body", "MODEL_VIEW")
+        if not new_representation:
+            return
+        new_representation = ifcopenshell.util.representation.resolve_representation(new_representation)
+        voided_objs_to_reload: set[bpy.types.Object] = set()
+        for rel in opening.HasFillings:
+            filling_type = ifcopenshell.util.element.get_type(rel.RelatedBuildingElement)
+            if not filling_type:
+                continue
+            old_template = self.get_type_opening_representation(filling_type)
+            if old_template is not None and old_template != new_representation:
+                # The edit gave this opening its own geometry; re-point the shared template
+                # map - and therefore every sibling occurrence mapping over it - at the
+                # edited geometry, then drop the now-orphaned old template.
+                for inverse in ifc_file.get_inverse(old_template):
+                    if inverse.is_a("IfcRepresentationMap"):
+                        inverse.MappedRepresentation = new_representation
+                ifcopenshell.api.geometry.remove_representation(ifc_file, representation=old_template)
+            self.set_type_opening_representation(filling_type, new_representation)
+
+            # Re-map every other occurrence's opening onto the type template so the edit
+            # propagates even to siblings that have their own independent opening geometry
+            # (i.e. openings that never shared the template's IfcRepresentationMap).
+            for occurrence in ifcopenshell.util.element.get_types(filling_type):
+                sibling_opening = (
+                    occurrence.FillsVoids[0].RelatingOpeningElement
+                    if getattr(occurrence, "FillsVoids", None)
+                    else None
+                )
+                if not sibling_opening or sibling_opening == opening:
+                    continue
+                if not self._remap_opening_to_template(sibling_opening, new_representation):
+                    continue
+                if sibling_opening.VoidsElements:
+                    voided_element = sibling_opening.VoidsElements[0].RelatingBuildingElement
+                    for part in ifcopenshell.util.element.get_parts(voided_element) or [voided_element]:
+                        if voided_obj := tool.Ifc.get_object(part):
+                            voided_objs_to_reload.add(voided_obj)
+
+        # Reload affected host objects so the viewport re-booleans with the propagated void.
+        for voided_obj in voided_objs_to_reload:
+            representation = tool.Geometry.get_active_representation(voided_obj)
+            if representation:
+                bonsai.core.geometry.switch_representation(
+                    tool.Ifc, tool.Geometry, obj=voided_obj, representation=representation
+                )
+
+    def _remap_opening_to_template(
+        self, opening: ifcopenshell.entity_instance, template_representation: ifcopenshell.entity_instance
+    ) -> bool:
+        """Point an opening's Body at the shared type template, purging its old standalone body.
+
+        :return: True if the opening was changed, False if it already maps over the template.
+        """
+        ifc_file = tool.Ifc.get()
+        old_body = ifcopenshell.util.representation.get_representation(opening, "Model", "Body", "MODEL_VIEW")
+        if old_body is not None and (
+            ifcopenshell.util.representation.resolve_representation(old_body) == template_representation
+        ):
+            return False
+        mapped_representation = ifcopenshell.api.geometry.map_representation(
+            ifc_file, representation=template_representation
+        )
+        # The mapped wrapper is the opening's own Body (the 'Reference' identifier belongs to
+        # the type template it maps over, not to the occurrence's representation).
+        mapped_representation.RepresentationIdentifier = "Body"
+        if old_body is not None:
+            ifcopenshell.api.geometry.unassign_representation(ifc_file, product=opening, representation=old_body)
+            ifcopenshell.api.geometry.remove_representation(ifc_file, representation=old_body)
+        ifcopenshell.api.geometry.assign_representation(ifc_file, product=opening, representation=mapped_representation)
+        return True
+
+    def promote_opening_to_type(self, filling_type: ifcopenshell.entity_instance) -> None:
+        """Promote a custom opening from an occurrence to a 'Reference' template on the type.
+
+        Called before a type is copied (``bim.duplicate_type``) so that a custom
+        (non-extrusion) opening, currently shared only between occurrences, is
+        anchored on the type itself and therefore carried to the copy. No-op if the
+        type already has a template or has no custom opening to promote.
+        """
+        if self.get_type_opening_representation(filling_type):
+            return
+        for occurrence in ifcopenshell.util.element.get_types(filling_type):
+            if not getattr(occurrence, "FillsVoids", None):
+                continue
+            opening = occurrence.FillsVoids[0].RelatingOpeningElement
+            if not self.should_preserve_opening(opening):
+                continue
+            representation = ifcopenshell.util.representation.get_representation(
+                opening, "Model", "Body", "MODEL_VIEW"
+            )
+            representation = ifcopenshell.util.representation.resolve_representation(representation)
+            self.set_type_opening_representation(filling_type, representation)
+            return
+
     def get_existing_opening_occurrence_if_any(
         self, filling: ifcopenshell.entity_instance
     ) -> Union[ifcopenshell.entity_instance, None]:
@@ -1000,6 +1256,9 @@ class EditOpenings(Operator, tool.Ifc.Operator):
                     building_objs.update(similar_openings_building_objs)
                     if opening_edited:
                         tool.Geometry.run_geometry_update_representation(obj=opening_obj)
+                        # Persist the edited void onto the filling type's 'Reference' template so
+                        # it survives type duplication/append/switching and propagates to siblings.
+                        self.update_type_template_from_opening(opening_element)
                     else:
                         bonsai.core.geometry.edit_object_placement(
                             tool.Ifc, tool.Geometry, tool.Surveyor, obj=opening_obj

src/bonsai/bonsai/bim/module/project/operator.py

@@ -633,6 +633,7 @@ class AppendLibraryElement(bpy.types.Operator, tool.Ifc.Operator):
         if not element:
             return {"FINISHED"}
         if element.is_a("IfcTypeProduct"):
+            self.harvest_opening_template(element, library_file)
             self.import_type_from_ifc(element, context)
         elif element.is_a("IfcProduct"):
             # NOTE: Non-types are not exposed in UI directly
@@ -658,6 +659,57 @@ class AppendLibraryElement(bpy.types.Operator, tool.Ifc.Operator):
         bonsai.bim.handler.refresh_ui_data()
         return {"FINISHED"}
 
+    def harvest_opening_template(
+        self, type_element: ifcopenshell.entity_instance, library_file: ifcopenshell.file
+    ) -> None:
+        """Seed the appended type's 'Reference' opening template from a library instance.
+
+        A type carries no opening of its own (openings are occurrence-level via
+        IfcRelVoidsElement), so a custom opening would otherwise be lost on append and
+        regenerated as a default extrusion when occurrences are placed. If the library
+        file has an instance of this type whose opening is custom (non-extrusion), copy
+        that opening body onto the appended type as its 'Reference' template. No-op when
+        the type already carries a template (e.g. a Bonsai-authored library) or the
+        library has no such instance.
+        """
+        from bonsai.bim.module.model.opening import FilledOpeningGenerator
+
+        generator = FilledOpeningGenerator()
+        if generator.get_type_opening_representation(type_element):
+            return
+
+        library_type = library_file.by_id(self.definition)
+        if not library_type.is_a("IfcTypeProduct"):
+            return
+
+        for occurrence in ifcopenshell.util.element.get_types(library_type):
+            if not getattr(occurrence, "FillsVoids", None):
+                continue
+            opening = occurrence.FillsVoids[0].RelatingOpeningElement
+            library_representation = ifcopenshell.util.representation.get_representation(
+                opening, "Model", "Body", "MODEL_VIEW"
+            )
+            if not library_representation:
+                continue
+            library_representation = ifcopenshell.util.representation.resolve_representation(library_representation)
+            if all(item.is_a("IfcExtrudedAreaSolid") for item in library_representation.Items):
+                continue  # A generated extrusion - nothing custom worth preserving.
+
+            project_file = tool.Ifc.get()
+            representation = project_file.add(library_representation)
+            # file.add brings the library's own representation context across; point the
+            # copy at the project's Body context and drop the now-orphaned duplicate.
+            body_context = ifcopenshell.util.representation.get_context(
+                project_file, "Model", "Body", "MODEL_VIEW"
+            )
+            if body_context and representation.ContextOfItems != body_context:
+                orphan_context = representation.ContextOfItems
+                representation.ContextOfItems = body_context
+                if not project_file.get_inverse(orphan_context):
+                    project_file.remove(orphan_context)
+            generator.set_type_opening_representation(type_element, representation)
+            return
+
     def import_material_from_ifc(self, element: ifcopenshell.entity_instance, context: bpy.types.Context) -> None:
         self.file = tool.Ifc.get()
         logger = logging.getLogger("ImportIFC")

src/bonsai/bonsai/bim/module/type/operator.py

@@ -375,6 +375,14 @@ class DuplicateType(bpy.types.Operator, tool.Ifc.Operator):
         obj = tool.Ifc.get_object(element)
         if not obj:
             return {"FINISHED"}
+        # Anchor any custom (non-extrusion) opening on the source type before the
+        # copy so it is carried to the duplicate as a 'Reference' template, rather
+        # than regenerated as a default extrusion on the new type's occurrences.
+        if element.is_a("IfcElementType"):
+            from bonsai.bim.module.model.opening import FilledOpeningGenerator
+
+            FilledOpeningGenerator().promote_opening_to_type(element)
+
         new_obj = obj.copy()
         if obj.data:
             new_obj.data = obj.data.copy()

src/bonsai/bonsai/tool/geometry.py

@@ -1206,7 +1206,23 @@ class Geometry(bonsai.core.tool.Geometry):
 
         for element in element_types:
             if obj := tool.Ifc.get_object(element):
-                if representation := ifcopenshell.util.representation.get_representation(element, context):
+                # A type may hold several representations in one context (e.g. a 'Body' body
+                # plus a 'Reference' opening template), and get_representation() matches only
+                # by context. When base_representation is one of this type's own
+                # representations - i.e. we are reimporting it directly, such as switching to
+                # the Reference rep - render exactly that, otherwise the context lookup could
+                # return the wrong one. But element_types also contains each occurrence's
+                # type (see above), for which base_representation is not theirs; fall back to
+                # the context lookup there (and skip, as before, when it has none).
+                type_representations = [
+                    ifcopenshell.util.representation.resolve_representation(rm.MappedRepresentation)
+                    for rm in (element.RepresentationMaps or [])
+                ]
+                if base_representation in type_representations:
+                    representation = base_representation
+                else:
+                    representation = ifcopenshell.util.representation.get_representation(element, context)
+                if representation:
                     geometry = ifcopenshell.geom.create_shape(settings, representation)
                     mesh_name = tool.Loader.get_mesh_name_from_shape(geometry)
                     mesh = meshes.get(mesh_name)

src/bonsai/bonsai/tool/model.py

@@ -2124,6 +2124,13 @@ class Model(bonsai.core.tool.Model):
             if voided_obj is not None:
                 voided_objs.add(voided_obj)
 
+            # Preserve user-authored opening geometry (e.g. an IfcPolygonalFaceSet
+            # or other tessellation) instead of replacing it with a default extrusion.
+            from bonsai.bim.module.model.opening import FilledOpeningGenerator
+
+            if FilledOpeningGenerator().is_opening_representation_custom(opening):
+                continue
+
             body = tool.Geometry.get_body_representation(opening)
             if body is None:
                 continue

src/ifcopenshell-python/ifcopenshell/api/type/map_type_representations.py

@@ -94,6 +94,13 @@ def map_type_representations(
         ifcopenshell.api.geometry.remove_representation(file, representation=representation)
     for representation_map in relating_type.RepresentationMaps:
         representation = representation_map.MappedRepresentation
+        # 'Reference' representations are, per IfcShapeRepresentation, "not part of
+        # the Body representation" (used e.g. for opening geometries excluded from an
+        # implicit Boolean operation). They may be carried on a type purely as a
+        # template (e.g. a shared opening body) and must not be mapped onto
+        # occurrences as their own geometry.
+        if representation.RepresentationIdentifier == "Reference":
+            continue
         mapped_representation = ifcopenshell.api.geometry.map_representation(file, representation=representation)
         ifcopenshell.api.geometry.assign_representation(
             file,