STEP export: Fusion round-trip fixes (sense, analytic surfaces, horn torus)

- Surfaces of revolution follow ISO 10303-42 strictly in reader and writer: the
  normal is d/d(angle) x d/d(profile), the opposite of truck's revolution, as
  Fusion reads it (fixes Fusion inverting fillet sphere corners and the dimple).
  step_orientation_errors flags faces whose loop runs clockwise round their
  normal; engine, oracle and kernel round trips assert it.
- Revolved faces with analytic profiles are written as native PLANE,
  CYLINDRICAL/CONICAL/SPHERICAL/TOROIDAL surfaces, and the pieces truck splits
  a revolution into are merged back into one face per surface (with a seam
  edge for full turns), so face counts match other systems.
- A horn torus (tight sweep: tube touching its axis) is written as one rational
  B-spline face whose loop passes the pole twice, with truck's zero-length pole
  edges collapsed, instead of a degenerate surface of revolution; the reader
  starts such figure-eight loops off the pole (Fusion's own part 50 now imports
  with the right volume).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

vendor/README.md

@@ -21,9 +21,10 @@ Only the writer (`out`) is used; SolveCraft reads STEP with its own reader.
 Changes:
 - `out/geometry.rs`: an `INTERSECTION_CURVE`'s second surface was written at the first
   surface's entity index, so every boolean-made edge produced duplicate entity ids.
-- `out/geometry.rs`: surfaces of revolution carry the right `same_sense`: truck's revolution
-  has the same parameterisation and normal as ISO 10303-42 (the writer flipped it), and a
-  mirroring transform reverses the normal.
+- `out/geometry.rs`: surfaces of revolution carry the right `same_sense` for inverted and
+  mirrored revolutions (ISO 10303-42 parameterises them by angle then profile, so their normal
+  is the opposite of truck's; a mirroring transform reverses it again), and the modeling-surface
+  wrapper passes the revolution's sense through instead of always `true`.
 - `lib.rs`: compiler warnings no longer fail the build. Example and test targets are dropped
   (their sources are not vendored).