Highlight partner wall on link-toggle hover

Hovering a wall-junction link-toggle icon today only swaps the icon
shape — the user doesn't see which wall the click will disconnect from
until after they click. ATPATH (T-junction) configurations especially
make the partner ambiguous when multiple connections sit close together.

On hover, paint a wireframe bbox around the partner wall using the same
shader, constants and color the array module already established for
its layer-children highlight (POLYLINE_UNIFORM_COLOR, decorator_color_special,
line width 1.8, alpha 0.8). The line-width / alpha constants in decorator.py
are renamed from _ARRAY_LAYER_BBOX_LINE_* to _BBOX_HIGHLIGHT_LINE_* and
shared between draw_array_layer_children_bbox and the new
draw_wall_partner_bbox so the two highlights stay in lockstep.

The trigger lives in a new GizmoWallLinkToggle subclass in wall.py
which keeps the base gizmos.GizmoLinkToggle generic (per the
generic-naming convention for shared widgets). The subclass's draw()
calls super().draw(context) then on self.is_highlight outlines its
partner_obj via the shared decorator helper. Same trigger pattern as
GizmoArrayLayerIndicator.

Blender's Gizmo API exposes target_set_operator but no symmetric
getter, so the partner reference can't be read back from the bound
operator handle. Instead GizmoWallUnjoinSingle.position_gizmos
mirrors the resolved partner_obj onto each visible icon every frame
next to the existing other_wall_guid write — the icon's draw() reads
from its own __slots__-declared attribute.

A forward-compat AST test pins the contract: GizmoWallLinkToggle.draw
must reference is_highlight and call draw_wall_partner_bbox. Catches
the regression where someone tidies the draw() override into super()
or replaces the shared helper with an ad-hoc draw call.

Generated with the assistance of an AI coding tool.

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

@@ -108,6 +108,7 @@ classes = (
     wall.GizmoWallFilletPreview,
     wall.GizmoWallFilletReedit,
     wall.GizmoWallJoinIntersection,
+    wall.GizmoWallLinkToggle,
     wall.GizmoWallUnjoinSingle,
     wall.JoinWallsIntersection,
     wall.MergeWall,

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

@@ -2233,8 +2233,8 @@ def draw_polyline_segments(
     gpu.state.blend_set("NONE")
 
 
-_ARRAY_LAYER_BBOX_LINE_WIDTH = 1.8
-_ARRAY_LAYER_BBOX_LINE_ALPHA = 0.8
+_BBOX_HIGHLIGHT_LINE_WIDTH = 1.8
+_BBOX_HIGHLIGHT_LINE_ALPHA = 0.8
 _ARRAY_LAYER_BBOX_MAX_CHILDREN = 200
 
 
@@ -2283,8 +2283,31 @@ def draw_array_layer_children_bbox(
         context,
         segments,
         color,
-        _ARRAY_LAYER_BBOX_LINE_ALPHA,
-        _ARRAY_LAYER_BBOX_LINE_WIDTH,
+        _BBOX_HIGHLIGHT_LINE_ALPHA,
+        _BBOX_HIGHLIGHT_LINE_WIDTH,
+    )
+
+
+def draw_wall_partner_bbox(
+    context: bpy.types.Context,
+    partner_obj: bpy.types.Object,
+) -> None:
+    """Paint a wireframe bbox around ``partner_obj`` in the same 3D pass.
+    Called inline from gizmo ``draw()`` methods so the highlight tracks the
+    hover cursor one-for-one — no POST_VIEW handler, no timing lag.
+
+    Silently no-ops if the object has no bounding box (e.g. Empties)."""
+    segments = bbox_world_edges(partner_obj)
+    if not segments:
+        return
+    prefs = tool.Blender.get_addon_preferences()
+    color = prefs.decorator_color_special[:3]
+    draw_polyline_segments(
+        context,
+        segments,
+        color,
+        _BBOX_HIGHLIGHT_LINE_ALPHA,
+        _BBOX_HIGHLIGHT_LINE_WIDTH,
     )
 
 

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

@@ -3546,6 +3546,36 @@ class GizmoWallJoinIntersection(bpy.types.GizmoGroup, _WallGeomCachedBillboardin
         self.merge_icon.hide = True
 
 
+class GizmoWallLinkToggle(gizmo.GizmoLinkToggle, bpy.types.Gizmo):
+    """Link-toggle glyph with a partner-wall highlight on hover. The owning
+    gizmo group writes the partner Blender object onto each icon every frame
+    via ``partner_obj``; on ``is_highlight`` the partner's bbox is outlined
+    inline so the user sees which wall the click will disconnect from
+    before committing.
+
+    The partner reference is stashed on the gizmo instance rather than
+    read back from the bound operator handle because Blender's Gizmo API
+    exposes ``target_set_operator`` for binding but no symmetric getter."""
+
+    bl_idname = "VIEW3D_GT_wall_link_toggle"
+    __slots__ = ("partner_obj",)
+
+    def setup(self) -> None:
+        super().setup()
+        self.partner_obj = None
+
+    def draw(self, context: bpy.types.Context) -> None:
+        super().draw(context)
+        if not self.is_highlight:
+            return
+        partner = self.partner_obj
+        if partner is None:
+            return
+        from bonsai.bim.module.model.decorator import draw_wall_partner_bbox
+
+        draw_wall_partner_bbox(context, partner)
+
+
 class GizmoWallUnjoinSingle(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMixin):
     """Activates when exactly one LAYER2 wall is selected. Surfaces an unjoin icon at
     every join location inferred from the wall's IfcRelConnectsPathElements inverse
@@ -3600,7 +3630,7 @@ class GizmoWallUnjoinSingle(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMix
         self.unjoin_op_props = []
         for _ in range(self.POOL_SIZE):
             icon = self.setup_icon_gizmo(
-                "VIEW3D_GT_link_toggle", default_color, highlight_color, "bim.unjoin_wall_path_connection"
+                "VIEW3D_GT_wall_link_toggle", default_color, highlight_color, "bim.unjoin_wall_path_connection"
             )
             icon.hide = True
             self.unjoin_icons.append(icon)
@@ -3652,6 +3682,11 @@ class GizmoWallUnjoinSingle(bpy.types.GizmoGroup, _WallGeomCachedBillboardingMix
             # save/reload, and any sit-in-the-undo-stack interlude between dispatch
             # and execute.
             self.unjoin_op_props[slot_idx].other_wall_guid = other_elem.GlobalId
+            # Mirror the partner reference onto the icon itself so its draw()
+            # can outline the partner on hover without a Gizmo-side getter on
+            # the bound operator (the API exposes target_set_operator with
+            # no symmetric reader).
+            icon.partner_obj = other_obj
 
 
 class GizmoWallFilletPreview(bpy.types.GizmoGroup):

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

@@ -28,6 +28,7 @@ rule is."""
 
 import ast
 import inspect
+import textwrap
 
 import pytest
 
@@ -59,3 +60,33 @@ def test_iter_path_connections_uses_path_connectable_predicate():
         "that strict predicate drops fillet-corner walls. Use "
         "is_path_connectable_wall instead."
     )
+
+
+def test_gizmo_wall_link_toggle_invokes_partner_bbox_helper():
+    """The wall subclass must call draw_wall_partner_bbox when its hover
+    state is active. Without this contract the partner-wall highlight
+    silently regresses if someone "tidies" the draw() override away."""
+    from bonsai.bim.module.model import wall as wall_module
+
+    source = textwrap.dedent(inspect.getsource(wall_module.GizmoWallLinkToggle.draw))
+    tree = ast.parse(source)
+    attr_names = {node.attr for node in ast.walk(tree) if isinstance(node, ast.Attribute)}
+    call_names: set[str] = set()
+    for node in ast.walk(tree):
+        if not isinstance(node, ast.Call):
+            continue
+        if isinstance(node.func, ast.Attribute):
+            call_names.add(node.func.attr)
+        elif isinstance(node.func, ast.Name):
+            call_names.add(node.func.id)
+
+    assert "is_highlight" in attr_names, (
+        "GizmoWallLinkToggle.draw must gate its highlight call on self.is_highlight — "
+        "without it the partner outline would draw every frame, not just on hover."
+    )
+    assert "draw_wall_partner_bbox" in call_names, (
+        "GizmoWallLinkToggle.draw must call draw_wall_partner_bbox to render the "
+        "partner outline. The shared composite in decorator.py is the canonical "
+        "trigger for this feature; replacing it with an ad-hoc draw call would "
+        "drift from the array-children bbox styling."
+    )