[Basnederveen]

What

Two failures when tessellating a curved face whose trim is not a UV rectangle (the earcut + refinement path):

1. A small hole at a coarse deflection: "curved trim loop requires at least four samples". A hole through a curved wall is bounded by intersection curves. At a deflection on the order of the hole's size, each of them gets one segment, so the hole's loop has two samples. Circles and ellipses already get a floor (12 per turn); intersection curves don't.
   raise_short_planar_loops becomes raise_short_loops. Planar loops keep exactly the old rule (at least three points, raising circles and ellipses). A curved face's trim loop is now raised to at least four samples, raising any curved edge, intersection curves included. Only loops that used to fail change.

2. A trim run off its corner vertex by rounding: "triangle orientation could not be resolved". The samples along an axis-parallel pcurve can differ by a few ulps from the corner vertex next to them, whose UV comes from the neighbouring pcurve (e.g. a run at v = 100 + 2 ulp ending at a corner at v = 100). The run is then not quite straight. Earcut cuts a near-zero-area ear along it, whose three 3D points lie on the edge (a circle in a plane normal to the axis), so the triangle's normal is perpendicular to the surface normal and the orientation dot product is exactly 0.
   In general_curved_trimmed_face, a ring coordinate within 64 ε (times the ring's magnitude) of the previous sample's is snapped to it. That is the same order as the 128 ε all_axis_aligned already uses. 3D sample points are unchanged.

Also, the orientation error and the refinement-triangle limit now name the face. The refinement-depth error already did.

Tests

• New tessellation/tests/curved_trims.rs, on a quarter of a thick-walled tube (cylinder faces 100 long) with a radial hole of radius 0.4 through both walls:
  • a_small_hole_in_a_curved_face_tessellates_at_a_coarse_deflection: deflections 2 and 5, every face gets triangles. Before: "curved trim loop requires at least four samples".
  • a_trim_run_off_its_corner_vertex_by_rounding_tessellates: the outer wall's run at v = 100 is moved 1, 2 and 4 rounding steps outward, as a pcurve evaluated at a corner can be. Before: "triangle orientation could not be resolved".
• cargo fmt --check, cargo clippy --all-targets -D warnings, and cargo test --all-targets (with CI=true) all pass, matching main.
• npm run check:source, check:duplicates and check:cycles pass. check:api needs a built SDK and wasn't run (no public API changes).

Files

• main/opengeometry/src/tessellation/loop_minimum.rs
• main/opengeometry/src/tessellation/tessellate.rs
• main/opengeometry/src/tessellation/trimmed_face.rs
• main/opengeometry/src/tessellation/mesh.rs
• main/opengeometry/src/tessellation/tests/curved_trims.rs (new), tests/mod.rs

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