Generalise opening gizmos + DRY toolbar plumbing

Add openings — GizmoWallAddOpening only fired when a wall was active +
co-selected with a non-host; slabs and roofs got no in-viewport handle.
GizmoHostAddOpening covers all three host types via is_supported_host,
dispatching walls to the axis-projection anchor and slabs/roofs to a
world-Z anchor lifted just above the host's top face (predictable
height regardless of the void's vertical position).

Show openings on hosts with their own parametric-edit toolbar —
GizmoRoofEdition gains an idle-row toggle_openings_gizmo parallel to
the wall's, parked at the cancel-slot X next to the pen. Visible only
when the host carries HasOpenings and the edit triad is idle. Roof
overrides get_element_height to return the mesh's world-AABB top in
object-local Z, so the WHOLE pen-row anchors visibly above sloped or
stepped roof bodies. The wall's idle-row toggle now also hides when
HasOpenings is empty.

Show openings on hosts WITHOUT a parametric-edit toolbar —
GizmoHostToggleOpenings scoped strictly to the fallback case: a single
host selected, HasOpenings non-empty, NOT a path-connectable wall, NOT
a parametric roof. Covers slabs today plus any foreign-authored IfcRoof
without BBIM_Roof. Anchored at object origin XY + world-AABB top Z.
When slab parametric-edit eventually lands, the slab predicate joins
the exclusion list and this gizmo's poll narrows automatically.

Operator move — ToggleWallOpenings was already host-agnostic; renamed
to ToggleHostOpenings in opening.py (bl_idname bim.toggle_host_openings).
Three callers (the wall idle-row binding, GizmoWallFilletToggleOpenings,
and workspace.py's hotkey_A_O for Alt+O) now route through the renamed
operator. The Alt+O binding is surfaced in the operator's
bl_description so it appears in F3 search and hover tooltips.

DRY refactors —
* GizmoWallAddOpening deleted (subsumed by GizmoHostAddOpening)
* tool.Blender.get_object_world_bounding_box added as the world-AABB
  sibling of the existing local helper; 3 inline call sites in
  tool/misc.py (set_object_origin_to_bottom, scale_object_to_height)
  and gizmos.py adopt it (2 other sites in drawing/operator.py and
  project/operator.py inherently need raw transformed corners for
  per-corner plane / NDC tests — not AABB candidates)
* BaseParametricGizmoGroup gains setup_pen_row_toggle_openings_icon +
  update_pen_row_toggle_openings_icon; wall + roof + any future host
  gizmo wire up the idle-row toggle with two one-line calls
* _resolve_active_host shared poll prologue between the two host
  gizmos (gate + selection count + active-in-selected + entity lookup
  + supported-host check)
* HasOpenings non-empty checks at 3 sites route through
  tool.Geometry.has_openings
* hotkey_A_O body collapsed to bpy.ops.bim.toggle_host_openings()

The forward-compat AST guard pinning "must accept fillet-corner walls"
retargets from GizmoWallAddOpening.poll to is_supported_host.

Generated with the assistance of an AI coding tool.

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

@@ -1501,24 +1501,11 @@ class SnapManager:
         nearby_objects = []
 
         for obj in mesh_objects:
-            bbox_corners = [obj.matrix_world @ Vector(corner) for corner in obj.bound_box]
-            if not bbox_corners:
+            if not obj.bound_box:
                 continue
-
-            bbox_min = Vector(
-                (
-                    min(c.x for c in bbox_corners),
-                    min(c.y for c in bbox_corners),
-                    min(c.z for c in bbox_corners),
-                )
-            )
-            bbox_max = Vector(
-                (
-                    max(c.x for c in bbox_corners),
-                    max(c.y for c in bbox_corners),
-                    max(c.z for c in bbox_corners),
-                )
-            )
+            bbox = tool.Blender.get_object_world_bounding_box(obj)
+            bbox_min = bbox["min_point"]
+            bbox_max = bbox["max_point"]
 
             closest = Vector(
                 (
@@ -5755,6 +5742,45 @@ class BaseParametricGizmoGroup:
     def get_element_height(self, props) -> float:
         return getattr(props, "overall_height", getattr(props, "height", 1.0))
 
+    def setup_pen_row_toggle_openings_icon(self) -> None:
+        """Create ``self.toggle_openings_gizmo`` bound to
+        ``bim.toggle_host_openings``. Subclasses call this from
+        ``setup_element_specific_gizmos`` to opt their host into the shared
+        idle-row toggle; pair with
+        ``update_pen_row_toggle_openings_icon`` in
+        ``_refresh_element_specific``."""
+        default_color, highlight_color = self.get_decoration_colors()
+        self.toggle_openings_gizmo = self._setup_icon_gizmo(
+            "VIEW3D_GT_add_opening",
+            default_color,
+            "bim.toggle_host_openings",
+            highlight_color,
+        )
+
+    def update_pen_row_toggle_openings_icon(self, context: bpy.types.Context, mw: "Matrix", props) -> None:
+        """Position ``self.toggle_openings_gizmo`` at the cancel-slot X next
+        to the pen in idle state; hide during edit (the validate/cancel row
+        owns that X) and when the active host carries no openings.
+
+        Subclasses opt in by calling
+        ``setup_pen_row_toggle_openings_icon`` in
+        ``setup_element_specific_gizmos`` and this method from
+        ``_refresh_element_specific``. No-op for groups that never
+        created the icon."""
+        if not hasattr(self, "toggle_openings_gizmo"):
+            return
+        obj = context.active_object
+        element = tool.Ifc.get_entity(obj) if obj is not None else None
+        has_openings = element is not None and tool.Geometry.has_openings(element)
+        if props.is_editing or not has_openings:
+            self.toggle_openings_gizmo.hide = True
+            return
+        self.toggle_openings_gizmo.hide = self.is_gizmo_hidden_by_modal(self.toggle_openings_gizmo)
+        icon_z = self.get_element_height(props) + self.ICON_Z_OFFSET
+        icon_y = self.get_icon_y_offset(context, mw)
+        world_pos = mw @ Vector((self.ICON_VALIDATE_X + self.ICON_CANCEL_X, icon_y, icon_z))
+        self.toggle_openings_gizmo.matrix_basis = billboarded_at(world_pos, self._frame_billboard_rot)
+
     def is_gizmo_hidden_by_modal(self, gizmo: bpy.types.Gizmo) -> bool:
         """Check if a gizmo should be hidden because a modal operator is active.
 

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

@@ -31,6 +31,7 @@ from . import (
     external,
     grid,
     handler,
+    host_add_opening_gizmo,
     mep,
     opening,
     product,
@@ -100,7 +101,8 @@ classes = (
     wall.ExtendWallToCursor,
     wall.FinishEditingWall,
     wall.FlipWall,
-    wall.GizmoWallAddOpening,
+    host_add_opening_gizmo.GizmoHostAddOpening,
+    host_add_opening_gizmo.GizmoHostToggleOpenings,
     wall.GizmoWallEdition,
     wall.GizmoWallExtendVertically,
     wall.GizmoWallFilletPreview,
@@ -116,7 +118,6 @@ classes = (
     wall.RotateWall90,
     wall.SplitWall,
     wall.SplitWallAtCursor,
-    wall.ToggleWallOpenings,
     wall.UnjoinWallPathConnection,
     wall.UnjoinWalls,
     wall.EnableWallFilletPreview,
@@ -135,6 +136,7 @@ classes = (
     opening.RemoveBoolean,
     opening.SelectBoolean,
     opening.ShowOpenings,
+    opening.ToggleHostOpenings,
     opening.UpdateOpeningsFocus,
     profile.ChangeCardinalPoint,
     profile.ChangeProfileDepth,

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

@@ -0,0 +1,221 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2026
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file was generated with the assistance of an AI coding tool.
+
+"""Generic single-click "Add Opening" gizmo for hosts (walls, slabs, roofs).
+
+One GizmoGroup serves every IFC host type that exposes ``HasOpenings``:
+parametric LAYER2 walls, any ``IfcSlab``, and any ``IfcRoof``. The poll
+guards host-host pairings so this gizmo never overlaps with the existing
+wall-join / extend-vertically gizmos. The positioner dispatches on element
+type — walls use axis-projection + camera-facing-Y math (which requires the
+parametric layer-set); slabs and roofs use a world-Z face bias driven by
+the void object's elevation against the host's bounding box."""
+
+import bpy
+from mathutils import Vector
+
+import bonsai.tool as tool
+from bonsai.bim.module.drawing import gizmos as gizmo
+from bonsai.bim.module.model.wall import (
+    _get_wall_geom_cached,
+    _wall_camera_facing_icon_y,
+    _wall_gizmo_poll_gate,
+    _WallGeomCachedBillboardingMixin,
+)
+
+
+def is_supported_host(element) -> bool:
+    """Total predicate (None → False). Walls accept either a parametric
+    LAYER2 wall OR a fillet-corner wall (both expose a usable axis +
+    layer-set for the anchor math); slabs and roofs only need the bound
+    box so any IfcSlab / IfcRoof qualifies regardless of parametric
+    modifier state."""
+    if element is None:
+        return False
+    return tool.Parametric.is_path_connectable_wall(element) or element.is_a("IfcSlab") or element.is_a("IfcRoof")
+
+
+def _resolve_active_host(context: bpy.types.Context, n_selected: int):
+    """Shared poll prologue: gizmo gate + selection cardinality + active-in-
+    selected + IFC entity lookup + supported-host predicate. Returns the
+    active element on success, ``None`` on any failure — callers chain their
+    feature-specific checks past the early-return."""
+    if not _wall_gizmo_poll_gate(context):
+        return None
+    selected = tool.Blender.get_selected_objects()
+    if len(selected) != n_selected:
+        return None
+    active = context.active_object
+    if active is None or active not in selected:
+        return None
+    element = tool.Ifc.get_entity(active)
+    if not element or not is_supported_host(element):
+        return None
+    return element
+
+
+class GizmoHostAddOpening(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMixin):
+    """Activates when a host element (wall / slab / roof) is the active object
+    and exactly one other selected object is *not* itself a host.
+
+    Renders a single ``VIEW3D_GT_add_opening`` icon at the void object's
+    projected location on the host. A click dispatches ``bim.add_opening``,
+    which handles any element exposing the ``HasOpenings`` inverse.
+
+    Per-frame positioning keeps the icon facing the camera as the viewport
+    orbits."""
+
+    bl_idname = "OBJECT_GGT_bim_host_add_opening"
+    bl_label = "Host Add Opening Gizmo"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "WINDOW"
+    bl_options = {"3D", "PERSISTENT"}
+
+    @classmethod
+    def poll(cls, context: bpy.types.Context) -> bool:
+        element = _resolve_active_host(context, n_selected=2)
+        if element is None:
+            return False
+        # The operator itself filters on HasOpenings, but checking here keeps
+        # the icon from appearing on host classes that can't accept openings
+        # in the active IFC schema.
+        if not hasattr(element, "HasOpenings"):
+            return False
+        active = context.active_object
+        other = next(o for o in tool.Blender.get_selected_objects() if o is not active)
+        # Host + host pairings are claimed by host-specific gizmos (wall-join,
+        # extend-vertical, …) — suppress here so the add-opening icon never
+        # stacks on top of them.
+        if is_supported_host(tool.Ifc.get_entity(other)):
+            return False
+        return True
+
+    def setup(self, context: bpy.types.Context) -> None:
+        default_color, highlight_color = self.get_decoration_colors()
+        self.add_opening_icon = self.setup_icon_gizmo(
+            "VIEW3D_GT_add_opening", default_color, highlight_color, "bim.add_opening"
+        )
+
+    def position_gizmos(self, context: bpy.types.Context) -> None:
+        host_obj = context.active_object
+        if not host_obj:
+            return
+        selected = tool.Blender.get_selected_objects()
+        other = next((o for o in selected if o is not host_obj), None)
+        if not other:
+            return
+        element = tool.Ifc.get_entity(host_obj)
+        if not element:
+            return
+
+        if tool.Parametric.is_path_connectable_wall(element):
+            world_pos = wall_anchor(context, self, host_obj, other)
+        else:
+            world_pos = layer3_anchor(host_obj, other)
+        if world_pos is None:
+            return
+        self.add_opening_icon.matrix_basis = gizmo.billboarded_at(world_pos, gizmo.get_billboard_rotation(context))
+
+
+def wall_anchor(
+    context: bpy.types.Context, group: bpy.types.GizmoGroup, wall_obj: bpy.types.Object, other: bpy.types.Object
+) -> Vector | None:
+    """World-space anchor for the add-opening icon on a wall host: void origin
+    projected onto the wall reference-line X (clamped to wall extents), lifted to
+    the camera-facing wall-local Y."""
+    geom = _get_wall_geom_cached(group, wall_obj)
+    if not geom:
+        return None
+    mw = wall_obj.matrix_world
+    wall_local = mw.inverted() @ other.matrix_world.translation
+    local_x = max(geom["anchor_x"], min(wall_local.x, geom["anchor_x"] + geom["length"]))
+    icon_y = _wall_camera_facing_icon_y(context, mw, geom)
+    base_world = mw @ Vector((local_x, icon_y, 0.0))
+    top_world = mw @ Vector((local_x, icon_y, geom["height"] + gizmo.BaseParametricGizmoGroup.ICON_Z_OFFSET))
+    return gizmo.BaseParametricGizmoGroup.pick_visible_anchor(context, base_world, top_world)
+
+
+def layer3_anchor(host_obj: bpy.types.Object, other: bpy.types.Object) -> Vector:
+    """World-space anchor for the add-opening icon on a LAYER3 host (slab / roof):
+    void's world XY, lifted just above the host's top face. Predictable height
+    regardless of where the void sits vertically — clicking the icon places the
+    opening at the void's XY, and the operator handles the actual cut depth."""
+    bbox = tool.Blender.get_object_world_bounding_box(host_obj)
+    anchor_xy = other.matrix_world.translation.xy
+    top_z = bbox["max_z"] + gizmo.BaseParametricGizmoGroup.ICON_Z_OFFSET
+    return Vector((anchor_xy.x, anchor_xy.y, top_z))
+
+
+def host_toggle_anchor(host_obj: bpy.types.Object) -> Vector:
+    """Object origin XY, lifted just above the topmost mesh vertex. Tracks
+    the parametric origin (useful reference even when the mesh extends
+    asymmetrically) and the visible top face (stays clear of sloped or
+    stepped bodies)."""
+    origin = host_obj.matrix_world.translation
+    top_z = tool.Blender.get_object_world_bounding_box(host_obj)["max_z"] + gizmo.BaseParametricGizmoGroup.ICON_Z_OFFSET
+    return Vector((origin.x, origin.y, top_z))
+
+
+class GizmoHostToggleOpenings(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMixin):
+    """Fallback toggle-openings icon for hosts that lack their own
+    parametric-edit toolbar — slabs today, plus any foreign-authored
+    IfcRoof that carries no BBIM_Roof pset (so ``GizmoRoofEdition`` doesn't
+    poll for it). Walls and parametric roofs already render an idle-row
+    toggle next to the pen and are excluded from this poll.
+
+    When slab parametric-edit lands the slab branch will pen-row-handle
+    its own toggle; updating the exclusion predicate here is the only
+    migration step needed."""
+
+    bl_idname = "OBJECT_GGT_bim_host_toggle_openings"
+    bl_label = "Host Toggle Openings Gizmo"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "WINDOW"
+    bl_options = {"3D", "PERSISTENT"}
+
+    @classmethod
+    def poll(cls, context: bpy.types.Context) -> bool:
+        element = _resolve_active_host(context, n_selected=1)
+        if element is None:
+            return False
+        if not tool.Geometry.has_openings(element):
+            return False
+        # Skip when a per-feature parametric-edit gizmo already surfaces
+        # an idle-row toggle for this element (wall: GizmoWallEdition;
+        # parametric roof: GizmoRoofEdition).
+        if tool.Parametric.is_path_connectable_wall(element):
+            return False
+        if tool.Parametric.is_roof(element):
+            return False
+        return True
+
+    def setup(self, context: bpy.types.Context) -> None:
+        default_color, highlight_color = self.get_decoration_colors()
+        self.toggle_openings_icon = self.setup_icon_gizmo(
+            "VIEW3D_GT_add_opening", default_color, highlight_color, "bim.toggle_host_openings"
+        )
+
+    def position_gizmos(self, context: bpy.types.Context) -> None:
+        host_obj = context.active_object
+        if not host_obj:
+            return
+        self.toggle_openings_icon.matrix_basis = gizmo.billboarded_at(
+            host_toggle_anchor(host_obj), gizmo.get_billboard_rotation(context)
+        )

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

@@ -737,6 +737,29 @@ class AddBoolean(Operator, tool.Ifc.Operator):
         tool.Root.reload_item_decorator()
 
 
+class ToggleHostOpenings(Operator, tool.Ifc.Operator):
+    bl_idname = "bim.toggle_host_openings"
+    bl_label = "Toggle Openings"
+    bl_description = "Show or hide opening fills (doors and windows) in the viewport\n\nHotkey: Alt+O"
+    bl_options = {"REGISTER", "UNDO"}
+
+    @classmethod
+    def poll(cls, context):
+        if not tool.Model.has_selected_ifc_objects():
+            cls.poll_message_set("No IFC objects selected.")
+            return False
+        return True
+
+    def _execute(self, context: bpy.types.Context) -> set[str]:
+        # Opening visibility is independent of host geometry — don't commit any
+        # active parametric edit; the user can keep editing the host.
+        if tool.Model.get_model_props().openings:
+            bpy.ops.bim.edit_openings(apply_all=True)
+        else:
+            bpy.ops.bim.show_openings()
+        return {"FINISHED"}
+
+
 class ShowOpenings(Operator, tool.Ifc.Operator):
     bl_idname = "bim.show_openings"
     bl_label = "Show Openings"

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

@@ -755,6 +755,25 @@ class GizmoRoofEdition(bpy.types.GizmoGroup, gizmo.BaseParametricGizmoGroup):
         self.set_dimension_gizmo_position("angle", mw, origin, (0, 0, 1))
         self.set_dimension_gizmo_position("roof_thickness", mw, origin, (0, 0, -1))
 
+    def get_element_height(self, props) -> float:  # noqa: ARG002
+        """Object-local Z of the mesh's topmost vertex, so the pen / validate /
+        cancel / cycle row anchors visibly above sloped or stepped roof
+        bodies rather than at the parametric ``props.height`` which may not
+        match the rendered apex on ANGLE-generation roofs."""
+        obj = bpy.context.active_object
+        if obj is None or not getattr(obj, "bound_box", None):
+            return 1.0
+        return max(c[2] for c in obj.bound_box)
+
+    def setup_element_specific_gizmos(self, context: bpy.types.Context) -> None:
+        """One idle-row icon outside the slot system: the ``toggle_openings``
+        button. Mirrors the wall idle row — pen + opening sit side by side
+        when the roof is selected and already carries at least one opening."""
+        self.setup_pen_row_toggle_openings_icon()
+
+    def _refresh_element_specific(self, context: bpy.types.Context, mw, props) -> None:
+        self.update_pen_row_toggle_openings_icon(context, mw, props)
+
 
 class EnableEditingRoofPath(bpy.types.Operator, tool.Ifc.Operator):
     bl_idname = "bim.enable_editing_roof_path"

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

@@ -2072,12 +2072,7 @@ class GizmoWallEdition(bpy.types.GizmoGroup, gizmo.BaseParametricGizmoGroup):
             "bim.extend_wall_height_to_cursor",
             highlight_color,
         )
-        self.toggle_openings_gizmo = self._setup_icon_gizmo(
-            "VIEW3D_GT_add_opening",
-            default_color,
-            "bim.toggle_wall_openings",
-            highlight_color,
-        )
+        self.setup_pen_row_toggle_openings_icon()
 
     def _refresh_element_specific(self, context: bpy.types.Context, mw: Matrix, props: "BIMWallProperties") -> None:
         """Position cursor-anchored gizmos and the wall-specific icon-row extras."""
@@ -2178,14 +2173,7 @@ class GizmoWallEdition(bpy.types.GizmoGroup, gizmo.BaseParametricGizmoGroup):
 
         Toggle-openings is NOT in the slot system — it surfaces in IDLE
         state (alongside the pen, not in the edit row), so it's positioned
-        manually here."""
-        if not hasattr(self, "toggle_openings_gizmo"):
-            return
-        icon_z = self.get_element_height(props) + self.ICON_Z_OFFSET
-        icon_y = self.get_icon_y_offset(context, mw)
-        billboard_rot = self._frame_billboard_rot
-
-        # --- Baseline variant visibility ---
+        via the base's shared helper here."""
         active_variant = self._BASELINE_TO_VARIANT.get(props.desired_offset_baseline)
         for variant in ("exterior", "center", "interior"):
             gz = getattr(self, f"baseline_{variant}_gizmo", None)
@@ -2195,16 +2183,7 @@ class GizmoWallEdition(bpy.types.GizmoGroup, gizmo.BaseParametricGizmoGroup):
                 gz.hide = self.is_gizmo_hidden_by_modal(gz)
             else:
                 gz.hide = True
-
-        # --- Idle-row toggle-openings (outside the slot system) ---
-        # Sits at the slot the cancel icon occupies during editing — that way the
-        # pen + openings pair is compact and visually grouped.
-        if not props.is_editing:
-            self.toggle_openings_gizmo.hide = self.is_gizmo_hidden_by_modal(self.toggle_openings_gizmo)
-            world_pos = mw @ Vector((self.ICON_VALIDATE_X + self.ICON_CANCEL_X, icon_y, icon_z))
-            self.toggle_openings_gizmo.matrix_basis = gizmo.billboarded_at(world_pos, billboard_rot)
-        else:
-            self.toggle_openings_gizmo.hide = True
+        self.update_pen_row_toggle_openings_icon(context, mw, props)
 
 
 def _apply_wall_extend_flips(
@@ -2359,29 +2338,6 @@ class RotateWall90(bpy.types.Operator, tool.Ifc.Operator):
         return {"FINISHED"}
 
 
-class ToggleWallOpenings(bpy.types.Operator, tool.Ifc.Operator):
-    bl_idname = "bim.toggle_wall_openings"
-    bl_label = "Toggle Openings"
-    bl_description = "Show or hide opening fills (doors and windows) in the viewport"
-    bl_options = {"REGISTER", "UNDO"}
-
-    @classmethod
-    def poll(cls, context):
-        if not tool.Model.has_selected_ifc_objects():
-            cls.poll_message_set("No IFC objects selected.")
-            return False
-        return True
-
-    def _execute(self, context: bpy.types.Context) -> set[str]:
-        # Opening visibility is independent of wall geometry — don't commit the
-        # active wall edit; the user can keep editing the wall.
-        if tool.Model.get_model_props().openings:
-            bpy.ops.bim.edit_openings(apply_all=True)
-        else:
-            bpy.ops.bim.show_openings()
-        return {"FINISHED"}
-
-
 def _wall_axis_world_segment_from_geom(obj: bpy.types.Object, geom: dict) -> tuple[Vector, Vector]:
     """Compose the world-space axis segment from an already-read ``geom`` dict.
     Used by the billboarding gizmo groups so a single cached IFC read drives both
@@ -3305,71 +3261,6 @@ def _wall_fillet_preview_walls(context: bpy.types.Context):
     return wall_a_obj, wall_b_obj
 
 
-class GizmoWallAddOpening(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMixin):
-    """Activates when a wall (active) and one non-wall blender object are co-selected.
-
-    Renders a single icon above the wall at the wall-local X corresponding to the other
-    object's projected origin. Clicking dispatches `bim.add_opening`, which lets the
-    existing FilledOpeningGenerator decide how the opening is applied.
-
-    Per-frame positioning via `BillboardingGizmoGroupMixin` ensures the icon
-    keeps facing the camera as the viewport is orbited."""
-
-    bl_idname = "OBJECT_GGT_bim_wall_add_opening"
-    bl_label = "Wall Add Opening Gizmo"
-    bl_space_type = "VIEW_3D"
-    bl_region_type = "WINDOW"
-    bl_options = {"3D", "PERSISTENT"}
-
-    @classmethod
-    def poll(cls, context: bpy.types.Context) -> bool:
-        if not _wall_gizmo_poll_gate(context):
-            return False
-        selected = tool.Blender.get_selected_objects()
-        if len(selected) != 2:
-            return False
-        active = context.active_object
-        if active is None or active not in selected:
-            return False
-        element = tool.Ifc.get_entity(active)
-        if not element or not tool.Parametric.is_path_connectable_wall(element):
-            return False
-        other = next(o for o in selected if o is not active)
-        # If the other object is also a wall, the wall-join gizmo handles it instead.
-        other_element = tool.Ifc.get_entity(other)
-        if other_element and tool.Parametric.is_path_connectable_wall(other_element):
-            return False
-        return True
-
-    def setup(self, context: bpy.types.Context) -> None:
-        default_color, highlight_color = self.get_decoration_colors()
-        self.add_opening_icon = self.setup_icon_gizmo(
-            "VIEW3D_GT_add_opening", default_color, highlight_color, "bim.add_opening"
-        )
-
-    def position_gizmos(self, context: bpy.types.Context) -> None:
-        wall_obj = context.active_object
-        if not wall_obj:
-            return
-        selected = tool.Blender.get_selected_objects()
-        other = next((o for o in selected if o is not wall_obj), None)
-        if not other:
-            return
-        geom = _get_wall_geom_cached(self, wall_obj)
-        if not geom:
-            return
-        mw = wall_obj.matrix_world
-        wall_local = mw.inverted() @ other.matrix_world.translation
-        local_x = max(geom["anchor_x"], min(wall_local.x, geom["anchor_x"] + geom["length"]))
-        # Place the icon on the camera-facing side of the wall, like the pen icon
-        # does for parametric edits — orbit the camera past the wall and the icon
-        # jumps to the visible face instead of being stranded behind it.
-        icon_y = _wall_camera_facing_icon_y(context, mw, geom)
-        icon_z = geom["height"] + gizmo.BaseParametricGizmoGroup.ICON_Z_OFFSET
-        world_pos = mw @ Vector((local_x, icon_y, icon_z))
-        self.add_opening_icon.matrix_basis = gizmo.billboarded_at(world_pos, gizmo.get_billboard_rotation(context))
-
-
 class GizmoWallExtendVertically(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMixin):
     """Activates when a LAYER3 element (typically a slab) is active and a LAYER2
     wall is co-selected. Mirrors the N-panel ``Extend To Underside`` button (which
@@ -4123,7 +4014,7 @@ class GizmoWallFilletToggleOpenings(bpy.types.GizmoGroup, _WallGeomCachedBillboa
             "VIEW3D_GT_add_opening",
             default_color,
             highlight_color,
-            "bim.toggle_wall_openings",
+            "bim.toggle_host_openings",
         )
 
     def position_gizmos(self, context: bpy.types.Context) -> None:

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

@@ -1442,10 +1442,7 @@ class Hotkey(bpy.types.Operator, tool.Ifc.Operator):
             bpy.ops.bim.enable_editing_extrusion_axis()
 
     def hotkey_A_O(self):
-        if tool.Model.get_model_props().openings:
-            bpy.ops.bim.edit_openings(apply_all=True)
-        else:
-            bpy.ops.bim.show_openings()
+        bpy.ops.bim.toggle_host_openings()
 
     def hotkey_C_E(self):
         if not bpy.context.selected_objects:

src/bonsai/bonsai/tool/blender.py

@@ -893,6 +893,34 @@ class Blender(bonsai.core.tool.Blender):
         }
         return bbox_dict
 
+    @classmethod
+    def get_object_world_bounding_box(cls, obj: bpy.types.Object) -> dict[str, Union[float, Vector]]:
+        """Same shape as ``get_object_bounding_box`` but with ``matrix_world``
+        applied — extents are computed across the 8 transformed corners, so
+        a rotated or scaled object reports its actual world-axis AABB rather
+        than the misleading transform of the local-space corners.
+
+        ``bound_box[0]`` / ``bound_box[6]`` are the local min/max corners but
+        do NOT correspond to the world AABB extremes once the object is
+        rotated, so min/max must be taken per-axis across all 8 corners."""
+        corners = [obj.matrix_world @ Vector(c) for c in obj.bound_box]
+        xs = [c.x for c in corners]
+        ys = [c.y for c in corners]
+        zs = [c.z for c in corners]
+        min_point = Vector((min(xs), min(ys), min(zs)))
+        max_point = Vector((max(xs), max(ys), max(zs)))
+        return {
+            "min_x": min_point.x,
+            "max_x": max_point.x,
+            "min_y": min_point.y,
+            "max_y": max_point.y,
+            "min_z": min_point.z,
+            "max_z": max_point.z,
+            "min_point": min_point,
+            "max_point": max_point,
+            "center": (min_point + max_point) / 2,
+        }
+
     @classmethod
     def select_and_activate_single_object(cls, context: bpy.types.Context, active_object: bpy.types.Object) -> None:
         for obj in context.selected_objects:

src/bonsai/bonsai/tool/misc.py

@@ -227,10 +227,8 @@ class Misc(bonsai.core.tool.Misc):
 
     @classmethod
     def set_object_origin_to_bottom(cls, obj: bpy.types.Object) -> None:
-        absolute_bound_box = [obj.matrix_world @ Vector(c) for c in obj.bound_box]
-        min_z = min([c[2] for c in absolute_bound_box])
         new_origin = obj.matrix_world.translation.copy()
-        new_origin[2] = min_z
+        new_origin[2] = tool.Blender.get_object_world_bounding_box(obj)["min_z"]
         assert isinstance(obj.data, bpy.types.Mesh)
         obj.data.transform(
             Matrix.Translation(
@@ -249,11 +247,8 @@ class Misc(bonsai.core.tool.Misc):
 
     @classmethod
     def scale_object_to_height(cls, obj: bpy.types.Object, height: float) -> None:
-        absolute_bound_box = [obj.matrix_world @ Vector(c) for c in obj.bound_box]
-        max_z = max([c[2] for c in absolute_bound_box])
-        min_z = min([c[2] for c in absolute_bound_box])
-        current_absolute_height = max_z - min_z
-        scale_factor = height / current_absolute_height
+        bbox = tool.Blender.get_object_world_bounding_box(obj)
+        scale_factor = height / (bbox["max_z"] - bbox["min_z"])
         obj.matrix_world @= Matrix.Scale(
             scale_factor, 4, obj.matrix_world.inverted().to_quaternion() @ Vector((0, 0, 1))
         )

src/bonsai/test/bim/module/model/conftest.py

@@ -0,0 +1,212 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2026
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file was generated with the assistance of an AI coding tool.
+
+"""Shared fixtures and factories for ``test/bim/module/model/`` gizmo and
+decorator tests.
+
+The boundary between Blender / IFC / Bonsai's ``tool.*`` layer is patched
+identically across many model-test files (viewport-state, selection, IFC
+entity lookup, modifier predicates, view-camera state). The ``patched_tool``
+fixture below centralises that patch stack so each test names only the
+boundary methods it cares about; everything else is left to production.
+
+Factory helpers (``make_obj``, ``make_element``, ``make_context``,
+``make_ifc_file``) replace near-identical local helpers that previously
+lived in each file.
+
+When to use these fixtures in a new test file:
+
+- Adding a gizmo / decorator test that patches ``tool.Blender`` or
+  ``tool.Ifc`` boundary methods? Request the ``patched_tool`` fixture
+  as a test parameter and call it as a context-manager factory.
+- Need a stub ``bpy.types.Object`` / ``ifcopenshell.entity_instance`` /
+  ``poll()`` context / ``ifcopenshell.file``? Import the matching factory
+  from this module rather than re-rolling locally.
+- Need to reset module-level state (e.g. a decorator cache token) between
+  tests? Define an ``@pytest.fixture(autouse=True)`` reset in the test
+  file itself — these stay file-local because they target state specific
+  to one decorator/module and globalising the reset would surprise
+  unrelated tests.
+
+Layout note: pure helpers (``make_*``) live alongside the fixture in this
+file rather than a sibling ``test_utils.py``. pytest's documented role for
+``conftest.py`` is fixtures, so this is a mild convention bend — kept here
+because the helper count is small and the dependencies (``tool``, ``Mock``)
+already need to be imported for the fixture itself. Split into a separate
+module if the helper count grows past ~6 or any helper picks up its own
+non-trivial dependencies."""
+
+import contextlib
+from types import SimpleNamespace
+from unittest.mock import MagicMock, Mock, patch
+
+import ifcopenshell
+import pytest
+
+from bonsai import tool
+
+
+def make_obj(*, session_uid=None, selected=True, **attrs):
+    """Mock a ``bpy.types.Object`` with attributes commonly read by gizmos.
+
+    ``session_uid`` is set only when provided so tests that don't care about
+    object identity (most poll() tests use ``object()`` sentinels) can use
+    ``make_obj()`` without a spurious uid. ``selected`` wires ``select_get()``
+    to return the given boolean. Extra attrs are set as plain attributes.
+
+    A bare ``Mock()`` is required because ``Mock(spec=bpy.types.Object)``
+    rejects ``select_get`` — Blender's C-registered methods aren't exposed
+    to Python introspection."""
+    obj = Mock()
+    if session_uid is not None:
+        obj.session_uid = session_uid
+    obj.select_get.return_value = selected
+    for name, value in attrs.items():
+        setattr(obj, name, value)
+    return obj
+
+
+def make_element(step_id=None, *, ifc_class=None, **attrs):
+    """Mock an ``ifcopenshell.entity_instance`` with the surfaces gizmos read.
+
+    ``step_id`` populates ``element.id()``. ``ifc_class`` wires ``is_a(name)``
+    to return True only when ``name == ifc_class``. Extra kwargs become plain
+    attributes (e.g. ``HasOpenings=()``)."""
+    element = Mock()
+    if step_id is not None:
+        element.id.return_value = step_id
+    if ifc_class is not None:
+        element.is_a.side_effect = lambda type_name: type_name == ifc_class
+    for name, value in attrs.items():
+        setattr(element, name, value)
+    return element
+
+
+def make_context(*, active=None, selected=(), scene=None):
+    """``SimpleNamespace`` stub with the ``poll()`` reads tests exercise:
+    ``active_object``, ``selected_objects``, and ``scene``. ``selected`` is
+    materialised to a list so tests can iterate without re-walking a generator.
+    ``scene`` defaults to an empty namespace so guards that walk
+    ``context.scene.BIMPreviewProperties`` (via ``getattr(..., default=None)``)
+    treat the preview as inactive — pass a custom namespace to activate."""
+    return SimpleNamespace(
+        active_object=active,
+        selected_objects=list(selected),
+        scene=scene if scene is not None else SimpleNamespace(),
+    )
+
+
+def make_ifc_file(elements_by_guid: dict | None = None) -> MagicMock:
+    """Mock ``ifcopenshell.file`` with ``spec=`` so attribute typos surface as
+    ``AttributeError`` instead of silently auto-creating a child mock.
+
+    When ``elements_by_guid`` is given, ``by_guid`` is wired to look up the
+    mapping and raise ``RuntimeError`` on a missing guid — same shape as the
+    real ifcopenshell.file behaviour, so a test that depends on orphan handling
+    sees an exception rather than a silent ``None``."""
+    f = MagicMock(spec=ifcopenshell.file, name="ifc_file")
+    if elements_by_guid is not None:
+
+        def _by_guid(guid):
+            try:
+                return elements_by_guid[guid]
+            except KeyError:
+                raise RuntimeError(f"no entity with guid {guid}")
+
+        f.by_guid.side_effect = _by_guid
+    return f
+
+
+@pytest.fixture
+def patched_tool():
+    """Context-manager factory for the ``tool.*`` boundary patches that nearly
+    every gizmo / decorator test repeats. Use as::
+
+        with patched_tool(viewport_gizmos=True, selected=[obj_a, obj_b],
+                          modifier_predicates={"is_wall": True}):
+            GizmoFoo.poll(context)
+
+    Only the kwargs you pass are patched — anything left as ``None`` (or
+    omitted) keeps production behaviour. Values can be:
+
+    - ``viewport_gizmos`` / ``view_top_down`` / ``addon_prefs``: passed to
+      ``return_value=`` of the corresponding patch.
+    - ``selected``: wrapped in ``set(...)`` for ``get_selected_objects``
+      (matches the production return type for ``poll()``-side reads).
+    - ``selected_list``: as-is for ``get_selected_objects`` when order
+      matters (some operators iterate it). Mutually exclusive with
+      ``selected`` — if both are passed, ``selected`` wins and
+      ``selected_list`` is ignored. Pass only one.
+    - ``entity``: either a callable (used as ``side_effect``) or a single
+      value (used as ``return_value``).
+    - ``modifier_predicates``: dict ``{predicate_name: bool_or_callable}``.
+      Callables are wired as ``side_effect``, bools as ``return_value``.
+    - ``screen_up``: ``return_value`` for ``get_screen_up_world``.
+
+    Patches close on context-manager exit via an ``ExitStack`` — no
+    ``try/finally`` bookkeeping in the test body."""
+
+    @contextlib.contextmanager
+    def _factory(
+        *,
+        viewport_gizmos=None,
+        addon_prefs=None,
+        selected=None,
+        selected_list=None,
+        entity=None,
+        modifier_predicates=None,
+        view_top_down=None,
+        screen_up=None,
+    ):
+        with contextlib.ExitStack() as stack:
+            if viewport_gizmos is not None:
+                stack.enter_context(
+                    patch.object(tool.Blender, "are_viewport_gizmos_enabled", return_value=viewport_gizmos)
+                )
+            if addon_prefs is not None:
+                stack.enter_context(patch.object(tool.Blender, "get_addon_preferences", return_value=addon_prefs))
+            if selected is not None:
+                stack.enter_context(patch.object(tool.Blender, "get_selected_objects", return_value=set(selected)))
+            elif selected_list is not None:
+                stack.enter_context(
+                    patch.object(tool.Blender, "get_selected_objects", return_value=list(selected_list))
+                )
+            if entity is not None:
+                if callable(entity):
+                    stack.enter_context(patch.object(tool.Ifc, "get_entity", side_effect=entity))
+                else:
+                    stack.enter_context(patch.object(tool.Ifc, "get_entity", return_value=entity))
+            if modifier_predicates:
+                for name, value in modifier_predicates.items():
+                    # Parametric feature-kind predicates live on tool.Parametric; the
+                    # remaining cardinality / non-parametric predicates (is_array_child,
+                    # is_slab, is_eligible_for_*) stay on tool.Blender.Modifier.
+                    target = tool.Parametric if hasattr(tool.Parametric, name) else tool.Blender.Modifier
+                    if callable(value):
+                        stack.enter_context(patch.object(target, name, side_effect=value))
+                    else:
+                        stack.enter_context(patch.object(target, name, return_value=value))
+            if view_top_down is not None:
+                stack.enter_context(patch.object(tool.Blender, "is_view_top_down", return_value=view_top_down))
+            if screen_up is not None:
+                stack.enter_context(patch.object(tool.Blender, "get_screen_up_world", return_value=screen_up))
+            yield
+
+    return _factory

src/bonsai/test/bim/module/model/test_host_add_opening_gizmo.py

@@ -0,0 +1,463 @@
+# Bonsai - OpenBIM Blender Add-on
+# Copyright (C) 2026
+#
+# This file is part of Bonsai.
+#
+# Bonsai is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Bonsai is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Bonsai.  If not, see <http://www.gnu.org/licenses/>.
+#
+# This file was generated with the assistance of an AI coding tool.
+
+"""Poll + positioning tests for ``GizmoHostAddOpening``.
+
+The gizmo dispatches on element type: walls keep the existing axis-projection
+math, while LAYER3 hosts (slabs, roofs) use a world-Z face bias derived from
+the void object's elevation. Each branch is exercised independently with
+mocks so the per-type contract is pinned without launching a full Blender
+modelling session."""
+
+import contextlib
+from types import SimpleNamespace
+from unittest.mock import patch
+
+import bpy
+import pytest
+from mathutils import Matrix, Vector
+
+import bonsai.tool as tool
+from test.bim.bootstrap import NewFile
+from test.bim.module.model.conftest import make_context
+
+pytestmark = pytest.mark.model
+
+
+# ---------------------------------------------------------------------------
+# poll() — entry gate per host type and per co-selection shape
+# ---------------------------------------------------------------------------
+
+
+_IFC_CLASS_BY_KIND = {
+    "wall": "IfcWall",
+    "slab": "IfcSlab",
+    "roof": "IfcRoof",
+    "plain": "IfcDiscreteAccessory",
+}
+
+
+class _FakeIfcEntity:
+    """Minimal stand-in for an ``ifcopenshell.entity_instance`` in poll tests.
+
+    Provides the two surfaces the gizmo's poll consults: ``is_a(type_name)``
+    (used directly by ``is_supported_host`` for slab/roof) and an optional
+    ``HasOpenings`` attribute (probed by the poll's ``hasattr`` guard)."""
+
+    def __init__(self, ifc_class: str, has_openings: bool = True):
+        self._ifc_class = ifc_class
+        if has_openings:
+            self.HasOpenings = ()
+
+    def is_a(self, type_name: str) -> bool:
+        return self._ifc_class == type_name
+
+
+def _build_poll_callbacks(selected, active_kind, other_kind):
+    """Build the ``(get_entity, is_path_connectable_wall)`` side-effect
+    callables that simulate one poll() invocation. ``active_kind`` /
+    ``other_kind`` accept ``"wall"``, ``"slab"``, ``"roof"``, ``"plain"``
+    (non-host IFC element), ``"mesh"`` (no IFC entity), or ``None``
+    (object outside the selection set).
+
+    Wall recognition goes through ``tool.Parametric.is_path_connectable_wall``
+    so fillet-corner walls (which have no LAYER2 usage) also surface the
+    add-opening icon; slab/roof use ``is_a`` on the fake entity so the
+    broadened class-based predicate is exercised."""
+    sentinels = {kind: _FakeIfcEntity(_IFC_CLASS_BY_KIND[kind]) for kind in _IFC_CLASS_BY_KIND}
+    # The "plain" sentinel lacks HasOpenings so the hasattr guard branch
+    # is reachable from the corresponding poll test.
+    sentinels["plain"] = _FakeIfcEntity(_IFC_CLASS_BY_KIND["plain"], has_openings=False)
+
+    def entity_for(kind):
+        if kind in (None, "mesh"):
+            return None
+        return sentinels[kind]
+
+    entity_map = {}
+    if len(selected) >= 1:
+        entity_map[id(selected[0])] = entity_for(active_kind)
+    if len(selected) >= 2:
+        entity_map[id(selected[1])] = entity_for(other_kind)
+
+    def get_entity(obj):
+        return entity_map.get(id(obj))
+
+    def is_path_connectable_wall(element):
+        return element is sentinels["wall"]
+
+    return get_entity, is_path_connectable_wall
+
+
+def _run_poll(
+    patched_tool, prefs_on=True, n_selected=2, active_in_selected=True, active_kind="wall", other_kind="mesh"
+):
+    from bonsai.bim.module.model.host_add_opening_gizmo import GizmoHostAddOpening
+
+    selected = [object() for _ in range(n_selected)]
+    active = selected[0] if (active_in_selected and selected) else object()
+    get_entity, is_path_connectable_wall = _build_poll_callbacks(selected, active_kind, other_kind)
+
+    with patched_tool(
+        viewport_gizmos=prefs_on,
+        selected=selected,
+        entity=get_entity,
+        modifier_predicates={"is_path_connectable_wall": is_path_connectable_wall},
+    ):
+        return GizmoHostAddOpening.poll(make_context(active=active, selected=selected))
+
+
+@pytest.mark.parametrize("host_kind", ["wall", "slab", "roof"])
+def test_poll_accepts_each_host_with_a_plain_mesh_void(host_kind, patched_tool):
+    assert _run_poll(patched_tool, active_kind=host_kind, other_kind="mesh") is True
+
+
+def test_poll_rejects_when_gizmo_toggle_off(patched_tool):
+    assert _run_poll(patched_tool, prefs_on=False) is False
+
+
+def test_poll_rejects_when_selection_count_is_not_two(patched_tool):
+    assert _run_poll(patched_tool, n_selected=1) is False
+    assert _run_poll(patched_tool, n_selected=3) is False
+
+
+def test_poll_rejects_when_active_is_not_in_selection(patched_tool):
+    assert _run_poll(patched_tool, active_in_selected=False) is False
+
+
+def test_poll_rejects_when_active_has_no_ifc_entity(patched_tool):
+    assert _run_poll(patched_tool, active_kind="mesh") is False
+
+
+def test_poll_rejects_when_active_is_not_a_host(patched_tool):
+    # "plain" sentinel is recognised as an IFC entity but is none of wall/slab/roof.
+    assert _run_poll(patched_tool, active_kind="plain") is False
+
+
+@pytest.mark.parametrize(
+    "active_kind,other_kind",
+    [
+        ("wall", "wall"),  # wall-join gizmo owns this
+        ("slab", "slab"),  # future slab-edit gizmo
+        ("roof", "roof"),
+        ("wall", "slab"),  # extend-vertically gizmo overlaps with this
+        ("slab", "wall"),
+        ("roof", "wall"),
+    ],
+)
+def test_poll_rejects_host_host_pairs(active_kind, other_kind, patched_tool):
+    """Host + host pairings must be suppressed so the icon never stacks with
+    the wall-join / extend-vertical / future slab-edit gizmos."""
+    assert _run_poll(patched_tool, active_kind=active_kind, other_kind=other_kind) is False
+
+
+def test_poll_rejects_active_host_without_has_openings(patched_tool):
+    # Real-world equivalent: an IFC class that the active schema strips
+    # ``HasOpenings`` from (e.g., a non-element subtype). The active sentinel
+    # is set up as a connectable wall but with no HasOpenings attribute.
+    from bonsai.bim.module.model.host_add_opening_gizmo import GizmoHostAddOpening
+
+    selected = [object(), object()]
+    active = selected[0]
+    host_sentinel = object()  # No HasOpenings attribute
+    other_sentinel = None
+
+    with patched_tool(
+        viewport_gizmos=True,
+        selected=selected,
+        entity=lambda o: host_sentinel if o is selected[0] else other_sentinel,
+        modifier_predicates={"is_path_connectable_wall": lambda e: e is host_sentinel},
+    ):
+        assert GizmoHostAddOpening.poll(make_context(active=active, selected=selected)) is False
+
+
+# ---------------------------------------------------------------------------
+# position_gizmos() — branch dispatch and per-branch anchor math
+# ---------------------------------------------------------------------------
+
+
+def _run_position_wall_branch(patched_tool, *, other_translation=(0.5, 0.0, 0.0), top_down=True):
+    """Drive the wall branch with stub IFC reads, returning the icon's
+    matrix_basis translation."""
+    from bonsai.bim.module.drawing import gizmos as gizmo_module
+    from bonsai.bim.module.model import host_add_opening_gizmo as host_mod
+    from bonsai.bim.module.model.host_add_opening_gizmo import GizmoHostAddOpening
+
+    geom = {"anchor_x": 0.0, "length": 2.0, "height": 3.0, "offset": 0.0, "thickness": 0.2}
+    wall_element = object()
+    active = SimpleNamespace(matrix_world=Matrix.Identity(4))
+    other = SimpleNamespace(matrix_world=Matrix.Translation(Vector(other_translation)))
+    selected = [active, other]
+    context = SimpleNamespace(active_object=active)
+    icon = SimpleNamespace(matrix_basis=None, hide=True)
+    self_stub = SimpleNamespace(add_opening_icon=icon)
+
+    with contextlib.ExitStack() as stack:
+        stack.enter_context(
+            patched_tool(
+                selected_list=selected,
+                entity=wall_element,
+                modifier_predicates={"is_path_connectable_wall": True},
+                view_top_down=top_down,
+                screen_up=Vector((0.0, 1.0, 0.0)),
+            )
+        )
+        stack.enter_context(patch.object(host_mod, "_get_wall_geom_cached", return_value=geom))
+        stack.enter_context(patch.object(host_mod, "_wall_camera_facing_icon_y", return_value=0.0))
+        stack.enter_context(patch.object(gizmo_module, "get_billboard_rotation", return_value=Matrix.Identity(4)))
+        stack.enter_context(
+            patch.object(
+                gizmo_module, "billboarded_at", side_effect=lambda pos, rot, scale=0.5: Matrix.Translation(pos)
+            )
+        )
+        GizmoHostAddOpening.position_gizmos(self_stub, context)
+    return icon.matrix_basis.translation
+
+
+def test_wall_branch_drops_height_lift_in_top_down_view(patched_tool):
+    """In plan view the wall-top Z lift must collapse to zero and the icon
+    must instead offset along screen-up — otherwise the icon stacks on top
+    of the wall outline and the user can't see it."""
+    from bonsai.bim.module.drawing.gizmos import BaseParametricGizmoGroup
+
+    pos = _run_position_wall_branch(patched_tool, top_down=True)
+    assert pos.z == pytest.approx(0.0)
+    assert pos.y == pytest.approx(BaseParametricGizmoGroup.SCREEN_STACK_OFFSET)
+
+
+def _run_position_layer3_branch(
+    patched_tool, *, host_world_z_range=(0.0, 0.2), other_z=1.0, other_xy=(0.7, 0.4), is_path_connectable_wall=False
+):
+    """Drive the LAYER3 (slab/roof) branch and return the icon translation.
+
+    ``host_world_z_range`` sets the world-Z extents of the host's bounding box
+    (the gizmo picks top vs bottom by comparing the void's Z to the box
+    midpoint). ``is_path_connectable_wall`` keeps a single helper for both
+    branches by flipping the dispatch predicate."""
+    from bonsai.bim.module.drawing import gizmos as gizmo_module
+    from bonsai.bim.module.model.host_add_opening_gizmo import GizmoHostAddOpening
+
+    z_min, z_max = host_world_z_range
+    # bound_box returns 8 corners in local space; we only need their world-Z
+    # range to drive the branch, so fix XY at zero and vary Z.
+    local_corners = [(0.0, 0.0, z_min), (0.0, 0.0, z_max)] * 4
+    host_obj = SimpleNamespace(matrix_world=Matrix.Identity(4), bound_box=local_corners)
+    other = SimpleNamespace(matrix_world=Matrix.Translation(Vector((other_xy[0], other_xy[1], other_z))))
+    selected = [host_obj, other]
+    context = SimpleNamespace(active_object=host_obj)
+    icon = SimpleNamespace(matrix_basis=None, hide=True)
+    self_stub = SimpleNamespace(add_opening_icon=icon)
+
+    host_element = object()
+    with contextlib.ExitStack() as stack:
+        stack.enter_context(
+            patched_tool(
+                selected_list=selected,
+                entity=host_element,
+                modifier_predicates={"is_path_connectable_wall": is_path_connectable_wall},
+            )
+        )
+        stack.enter_context(patch.object(gizmo_module, "get_billboard_rotation", return_value=Matrix.Identity(4)))
+        stack.enter_context(
+            patch.object(
+                gizmo_module, "billboarded_at", side_effect=lambda pos, rot, scale=0.5: Matrix.Translation(pos)
+            )
+        )
+        GizmoHostAddOpening.position_gizmos(self_stub, context)
+    return icon.matrix_basis.translation
+
+
+@pytest.mark.parametrize("other_z", [1.0, 0.1, -1.0])
+def test_layer3_branch_always_parks_above_top_face(patched_tool, other_z):
+    """Icon parks above the host's top face regardless of the void's Z —
+    predictable height every time. Void's XY is preserved so clicking the
+    icon dispatches the operator at the intended XY position."""
+    from bonsai.bim.module.drawing.gizmos import BaseParametricGizmoGroup
+
+    pos = _run_position_layer3_branch(patched_tool, host_world_z_range=(0.0, 0.2), other_z=other_z, other_xy=(0.7, 0.4))
+    assert pos.x == pytest.approx(0.7)
+    assert pos.y == pytest.approx(0.4)
+    assert pos.z == pytest.approx(0.2 + BaseParametricGizmoGroup.ICON_Z_OFFSET)
+
+
+# ---------------------------------------------------------------------------
+# is_supported_host() — predicate totality
+# ---------------------------------------------------------------------------
+
+
+def test_is_supported_host_returns_false_for_none():
+    """Total predicate: ``None`` short-circuits to False without raising."""
+    from bonsai.bim.module.model.host_add_opening_gizmo import is_supported_host
+
+    assert is_supported_host(None) is False
+
+
+def test_is_supported_host_accepts_bare_ifc_slab():
+    """The slab branch is class-based — any ``IfcSlab`` qualifies, even
+    without LAYER3 parametric usage. The positioner reads ``obj.bound_box``,
+    which works for both parametric and imported geometry."""
+    from bonsai.bim.module.model.host_add_opening_gizmo import is_supported_host
+
+    assert is_supported_host(_FakeIfcEntity("IfcSlab")) is True
+
+
+def test_is_supported_host_accepts_bare_ifc_roof():
+    """The roof branch is class-based, not pset-based — a bare ``IfcRoof``
+    imported from another IFC tool qualifies even without the Bonsai
+    BBIM_Roof parametric marker that ``tool.Parametric.is_roof``
+    would require."""
+    from bonsai.bim.module.model.host_add_opening_gizmo import is_supported_host
+
+    assert is_supported_host(_FakeIfcEntity("IfcRoof")) is True
+
+
+def test_is_supported_host_rejects_non_host_ifc_class():
+    """Non-host IFC classes are filtered — covers ``IfcCovering`` (which has
+    HasOpenings but is not a wall/slab/roof) and prevents the gizmo from
+    surfacing on arbitrary building elements."""
+    from bonsai.bim.module.model.host_add_opening_gizmo import is_supported_host
+
+    assert is_supported_host(_FakeIfcEntity("IfcCovering")) is False
+    assert is_supported_host(_FakeIfcEntity("IfcDiscreteAccessory")) is False
+
+
+# ---------------------------------------------------------------------------
+# End-to-end smoke: gizmo's target operator handles host + mesh-void selection
+# ---------------------------------------------------------------------------
+#
+# The gizmo binds ``bim.add_opening`` via ``setup_icon_gizmo`` — clicking the
+# icon dispatches that operator with the current selection set. The operator
+# has its own target/opening detection that swaps based on which selected
+# object carries an IFC entity. This smoke test pins that handoff: with a
+# host as the active object and a non-IFC mesh as the "void", the operator
+# creates an ``IfcOpeningElement`` linked to the host via the standard
+# ``HasOpenings`` inverse.
+
+
+class TestAddOpeningIntegrationOnSlab(NewFile):
+    def test_creates_opening_when_slab_is_active_with_mesh_void(self):
+        tool.Project.get_project_props().template_file = "IFC4 Demo Template.ifc"
+        bpy.ops.bim.create_project()
+        ifc_file = tool.Ifc.get()
+        slab_type = ifc_file.by_type("IfcSlabType")[0]
+        bpy.ops.bim.add_occurrence(relating_type_id=slab_type.id())
+        slab = ifc_file.by_type("IfcSlab")[0]
+        slab_obj = tool.Ifc.get_object(slab)
+        assert isinstance(slab_obj, bpy.types.Object)
+        assert len(slab.HasOpenings) == 0
+
+        void_obj = bpy.data.objects.new("VoidMesh", bpy.data.meshes.new("VoidMesh"))
+        bpy.context.scene.collection.objects.link(void_obj)
+        void_obj.matrix_world = void_obj.matrix_world.copy()
+        void_obj.matrix_world.translation = (
+            slab_obj.matrix_world.translation.x,
+            slab_obj.matrix_world.translation.y,
+            slab_obj.matrix_world.translation.z + 1.0,
+        )
+
+        tool.Blender.set_objects_selection(bpy.context, slab_obj, (slab_obj, void_obj))
+        bpy.ops.bim.add_opening()
+
+        assert len(slab.HasOpenings) == 1
+        opening = slab.HasOpenings[0].RelatedOpeningElement
+        assert opening.is_a("IfcOpeningElement")
+
+
+class TestAddOpeningPollOnForeignAuthoredSlab(NewFile):
+    def test_poll_resolves_true_for_slab_without_layer3_usage(self):
+        """An ``IfcSlab`` loaded from a non-Bonsai IFC carries no
+        ``IfcMaterialLayerSetUsage``, so ``tool.Blender.Modifier.is_slab``
+        rejects it — yet the gizmo's widened predicate accepts any
+        ``IfcSlab`` because the positioner only reads the bound box.
+        This pins the bare-class branch through the full ``poll`` path
+        with real bpy + ifcopenshell state."""
+        import ifcopenshell.api.material
+
+        from bonsai.bim.module.model.host_add_opening_gizmo import (
+            GizmoHostAddOpening,
+            is_supported_host,
+        )
+
+        tool.Project.get_project_props().template_file = "IFC4 Demo Template.ifc"
+        bpy.ops.bim.create_project()
+        ifc_file = tool.Ifc.get()
+        slab_type = ifc_file.by_type("IfcSlabType")[0]
+        bpy.ops.bim.add_occurrence(relating_type_id=slab_type.id())
+        slab = ifc_file.by_type("IfcSlab")[0]
+        slab_obj = tool.Ifc.get_object(slab)
+        assert isinstance(slab_obj, bpy.types.Object)
+
+        # Strip every material association so the slab has no direct
+        # LayerSetUsage and nothing to inherit from the type. The slab is
+        # now a foreign-authored IFC class in everything but provenance.
+        ifcopenshell.api.material.unassign_material(ifc_file, products=[slab, slab_type])
+        assert tool.Blender.Modifier.is_slab(slab) is False
+        assert is_supported_host(slab) is True
+
+        void_obj = bpy.data.objects.new("VoidMesh", bpy.data.meshes.new("VoidMesh"))
+        bpy.context.scene.collection.objects.link(void_obj)
+        void_obj.matrix_world = void_obj.matrix_world.copy()
+        void_obj.matrix_world.translation = (
+            slab_obj.matrix_world.translation.x,
+            slab_obj.matrix_world.translation.y,
+            slab_obj.matrix_world.translation.z + 1.0,
+        )
+
+        tool.Blender.set_objects_selection(bpy.context, slab_obj, (slab_obj, void_obj))
+        assert GizmoHostAddOpening.poll(bpy.context) is True
+
+
+class TestAddOpeningPollOnForeignAuthoredRoof(NewFile):
+    def test_poll_resolves_true_for_roof_without_bbim_pset(self):
+        """A mesh-bodied ``IfcRoof`` promoted from a raw Blender mesh
+        carries no ``BBIM_Roof`` pset, so ``tool.Parametric.is_roof``
+        rejects it — yet the gizmo's widened predicate accepts any
+        ``IfcRoof`` because the positioner only reads the bound box. This
+        fixture mirrors how a foreign IFC roof loads (geometry + IFC
+        identity, no parametric markers)."""
+        from bonsai.bim.module.model.host_add_opening_gizmo import (
+            GizmoHostAddOpening,
+            is_supported_host,
+        )
+
+        tool.Project.get_project_props().template_file = "IFC4 Demo Template.ifc"
+        bpy.ops.bim.create_project()
+
+        bpy.ops.mesh.primitive_cube_add(size=2, location=(0, 0, 0))
+        roof_obj = bpy.context.active_object
+        assert roof_obj is not None
+        tool.Root.get_root_props().ifc_product = "IfcElement"
+        bpy.ops.bim.assign_class(ifc_class="IfcRoof")
+        roof = tool.Ifc.get_entity(roof_obj)
+        assert roof is not None and roof.is_a("IfcRoof")
+        assert tool.Parametric.is_roof(roof) is False
+        assert is_supported_host(roof) is True
+
+        void_obj = bpy.data.objects.new("VoidMesh", bpy.data.meshes.new("VoidMesh"))
+        bpy.context.scene.collection.objects.link(void_obj)
+        void_obj.matrix_world = void_obj.matrix_world.copy()
+        void_obj.matrix_world.translation = (
+            roof_obj.matrix_world.translation.x,
+            roof_obj.matrix_world.translation.y,
+            roof_obj.matrix_world.translation.z + 1.0,
+        )
+
+        tool.Blender.set_objects_selection(bpy.context, roof_obj, (roof_obj, void_obj))
+        assert GizmoHostAddOpening.poll(bpy.context) is True

src/bonsai/test/bim/module/model/test_wall_gizmos_forward_compat.py

@@ -135,29 +135,30 @@ def test_every_wall_gizmo_group_resolves_get_decoration_colors():
     )
 
 
-def test_gizmo_wall_add_opening_accepts_fillet_corner_active():
-    """``GizmoWallAddOpening.poll`` must gate on ``is_path_connectable_wall``,
-    not the strict ``is_wall`` predicate. Fillet-corner walls carry no LAYER2
-    usage by IFC spec, so the strict predicate rejects them and the
-    add-opening icon never surfaces over a curved corner — symmetry with the
-    join / unjoin / extend wall gizmos (all of which already poll on the
-    looser predicate) is required for the user to drop openings into fillet
+def test_host_add_opening_accepts_fillet_corner_active():
+    """``is_supported_host`` (the gate ``GizmoHostAddOpening.poll`` dispatches
+    through) must classify walls via ``is_path_connectable_wall``, not the
+    strict ``is_wall`` predicate. Fillet-corner walls carry no LAYER2 usage
+    by IFC spec, so the strict predicate rejects them and the add-opening
+    icon never surfaces over a curved corner — symmetry with the join /
+    unjoin / extend wall gizmos (all of which already poll on the looser
+    predicate) is required for the user to drop openings into fillet
     corners at all."""
-    from bonsai.bim.module.model.wall import GizmoWallAddOpening
+    from bonsai.bim.module.model.host_add_opening_gizmo import is_supported_host
 
-    source = textwrap.dedent(inspect.getsource(GizmoWallAddOpening.poll))
+    source = textwrap.dedent(inspect.getsource(is_supported_host))
     tree = ast.parse(source)
     attr_names = {node.attr for node in ast.walk(tree) if isinstance(node, ast.Attribute)}
 
     assert "is_path_connectable_wall" in attr_names, (
-        "GizmoWallAddOpening.poll must gate on tool.Parametric.is_path_connectable_wall "
-        "for both the active element and the partner-exclusion check. The strict "
-        "is_wall predicate hides the add-opening gizmo over every fillet-corner wall."
+        "is_supported_host must gate walls on tool.Parametric.is_path_connectable_wall. "
+        "The strict is_wall predicate hides the add-opening gizmo over every "
+        "fillet-corner wall."
     )
     assert "is_wall" not in attr_names, (
-        "GizmoWallAddOpening.poll must NOT call .is_wall — that strict predicate "
-        "drops fillet-corner walls. Use is_path_connectable_wall instead, matching "
-        "the host gate every other wall-state gizmo group uses."
+        "is_supported_host must NOT call .is_wall — that strict predicate drops "
+        "fillet-corner walls. Use is_path_connectable_wall instead, matching the "
+        "host gate every other wall-state gizmo group uses."
     )