fix(hatch): mirrored-block arcs — bump acadrust, document angle convention

Hatches inside mirrored INSERTs (x_scale = -1, e.g. the *U blocks in
xref_Plan-Sade) drew some boundary arcs swept the wrong way, covering
huge complementary regions — in the pattern clip before EXPLODE, and in
both pattern and boundary wires after (the exploded entity bakes the
broken angles).

Root cause was in acadrust's transform_hatch, not the renderer: DXF
stores CW (ccw=false) boundary-arc angles MIRRORED (verified against
AutoCAD output by endpoint continuity — mirrored interpretation gives
Δ=0.0 against adjacent edges), and the transform stored geometric angles
after flipping the direction flag. The legacy (TAU-θ) sampling flip in
arc_signed_span is exactly right for file data and stays; its comment now
records the verification so the convention isn't "fixed" away again.

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

Cargo.lock

@@ -56,7 +56,7 @@ checksum = "366ffbaa4442f4684d91e2cd7c5ea7c4ed8add41959a31447066e279e432b618"
 [[package]]
 name = "acadrust"
 version = "0.3.4"
-source = "git+https://github.com/HakanSeven12/acadrust?branch=main#db110124facbab3fbb4d947871638d73dc8b8a3a"
+source = "git+https://github.com/HakanSeven12/acadrust?branch=main#ddd6888b261cb104fcf3acd6e62dc197f5d4e769"
 dependencies = [
  "ahash",
  "anyhow",

src/scene/tess_util.rs

@@ -31,6 +31,15 @@ pub type FallbackGeometry = (
 /// semantics are preserved on real files. (Wrap-through-2π is a known
 /// edge case in that convention; do not "fix" it without a wider audit
 /// of how upstream writers emit CW boundary arcs.)
+///
+/// VERIFIED against real AutoCAD output (KSR-039 DWG, CW arc edges with
+/// line neighbours): the stored angles of a `ccw = false` arc edge are
+/// MIRRORED — the true point is `center + r·(cos(TAU-θ), sin(TAU-θ))`.
+/// Sampling the mirrored parameter directly (this function's flip) gives
+/// exact endpoint continuity with the adjacent edges (Δ = 0.000000),
+/// while interpreting them as true angles lands tens of units away. Any
+/// code that *produces* CW boundary arcs (mirror transforms, explode)
+/// must therefore store mirrored angles, not geometric ones.
 pub fn arc_signed_span(start: f64, end: f64, ccw: bool) -> (f64, f64) {
     const TAU: f64 = std::f64::consts::TAU;
     let (sa, ea) = if ccw { (start, end) } else { (TAU - start, TAU - end) };