This PR is to fix #6896 but during testing copilots solution a second issue was discovered and fixed. Namely that multiple loops in the slab would cause an exception.

Shift+A → Add From Perimeter generated walls from slab perimeter vertices only, so IfcIndexedPolyCurve arcs were treated like straight chords. This change makes slab-to-wall generation interpret arc segments and circles and emit contiguous wall segments along sampled arc geometry.

Changes

• Arc-aware perimeter extraction

  • DumbWallGenerator.derive_from_slab() now branches on curve content: existing polyline path for non-arc curves; arc-aware path for IfcIndexedPolyCurve with arc segments.
  • Added _curve_has_arc_segments() to detect arc-bearing segment payloads across wrapper representations.

• Arc segment sampling to wall segments

  • Added _derive_points_from_arc_segments() to convert IfcArcIndex triplets into sampled points via tool.Cad.create_arc_segments(...).
  • Ensures start→end arc traversal consistency before wall creation, so segment ordering stays contiguous around the perimeter.

• Perimeter robustness

  • Added _world_xy_point() for consistent IFC→world conversion.
  • Added point deduplication tolerance and explicit loop closure.
  • For non-arc indexed line segments, all referenced indices are now emitted (not only endpoints), preserving multi-index segment detail.

Creating walls from a slab failed when the slab outer curve was IfcCircle, because the wall generator only handled polyline-like curves and raised Unsupported polyline type: IfcCircle. This change adds a dedicated circle path so circular slabs can produce wall segments via Shift+A without throwing.

Changes

• Wall generation: curve-type coverage

  • Added IfcCircle handling in DumbWallGenerator.derive_from_slab().
  • Kept existing behavior for indexed polycurves (including arc segments) and other supported polyline curves.

• Circle perimeter extraction

  • Added _derive_points_from_circle(...) to sample circular perimeters using SLAB_ARC_RESOLUTION.
  • Applies slab object/world transform and circle local placement (IfcAxis2Placement2D) before wall segment creation.
  • Closes the sampled loop explicitly for consistent downstream segment iteration.

• AI-generated contribution

  • This PR includes code generated/modified with the assistance of an AI coding tool.

When a slab has multiple separate closed loops, its swept area is IfcCompositeProfileDef (which has Profiles, not OuterCurve). Calling Shift+A to draw walls from such a slab raised AttributeError: entity instance of type 'IFC4.IfcCompositeProfileDef' has no attribute 'OuterCurve'.

• derive_from_slab (wall.py): detect IfcCompositeProfileDef and iterate over each of its Profiles rather than assuming a single OuterCurve. Each closed loop is processed independently and walls are generated for all of them. Single-profile slabs are unaffected.

Two bugs when generating walls from a slab whose swept area is IfcCompositeProfileDef (multiple separate closed loops):

1. Crash — extrusion.SweptArea.OuterCurve raises AttributeError because IfcCompositeProfileDef has Profiles, not OuterCurve.
2. Phantom walls far outside the bounding box — the post-generation DumbWallJoiner loop treated all walls as a single circular ring, cross-connecting the last wall of loop N to the first wall of loop N+1. Since those walls never intersect, the computed join point lands far from the slab.

Changes

• derive_from_slab: detects IfcCompositeProfileDef and iterates over each constituent profile, building walls per loop independently; returns a list[list[wall]] (one inner list per closed loop) instead of a flat list.
• DrawWallsFromSlab._execute: updated to iterate over wall groups, running the DumbWallJoiner ring-connect only within each loop's own walls.

Single-profile slabs are unaffected — wall_groups has one element and the behaviour is identical to before.