Spline entities now expose fit_points (or control_points when no fit
points are defined) as key_vertices, enabling Endpoint and Midpoint
snap to reach spline construction points.
TextStyle is_backward flag is applied by negating the width_factor,
producing horizontally mirrored text. is_upside_down rotates the text
180°. Both tessellate_text_ex and text_local_bounds now handle negative
width_factor without clamping it to zero.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Empty LwPolyline and single-control-point Spline fallbacks were calling
builder::line(&v, &v) with the same Rc vertex, triggering the
truck-topology panic "Two same vertices cannot construct an edge."
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
