Summary

Pure readability pass, net −108 lines (251+/359−) with zero behavior change. Three thematic commits:

PyO3 layer — impl From<TriangulationError> for PyErr replaces the inherent into_pyerr, so the 31 call sites that wrapped every core call in .map_err(TriangulationError::into_pyerr) now just use ?. This was the single biggest source of awkward rustfmt line splits; most bindings collapse back to one line per call. Also: a given() helper for the repeated "absent argument or explicit Python None" three-arm matches, and the eight SimplicesProxy set operators delegate through one shared set_op/set_rop pair.

Geometry — coord_2d/coord_3d replace the robust::Coord closures redefined inline in every predicate, sign() replaces the repeated three-way if/else blocks, and validate_simplex() dedupes the "dim+1 points of equal dimension" check spelled out in four functions.

Core — TriangulationError::value() collapses the three-line error returns, containing() uses plain loops instead of dozen-line map/filter chains, facet_neighbour() names the "other simplex across this facet" lookup shared by the walk and opposing_vertices, detach_vertex() dedupes the failed-insertion rollback duplicated between extend_hull and add_point, and summed_volume trades a turbofish try_fold for a for loop.

Verification (identical to main on every axis)

• pytest: 112 passed; cargo test --lib --tests: 18 passed
• Stress sweeps (50 seeds × 4 patterns × 2D/3D): byte-for-byte identical classification including per-pattern rejection totals (10/21/615/7/117), i.e. the refactor provably didn't alter any numerical path
• A/B benchmark: unchanged (2D 5k 0.134 s, 3D 2k 0.156 s, 4D 500 0.241 s, hull-heavy unchanged)
• pre-commit clean