flatten_bulges chops a semicircle into an even number of chords (36 for
r=50, 12 for r=5), so a flattened vertex lands exactly on the apex — the
axis of symmetry, the one place a P&ID line most plausibly meets a
crossing jump. segments_cross treats a vertex hit as a junction, so both
neighbouring chords dropped it and the arc contributed 0: the (45,0)->(55,0)
bulge -1 jump reported crossings 0 at x=50 and 1 at x=50.3 or x=49, the
plan's own (0,0)->(100,0) semicircle 0 at x=50, and the mirrored frame
(extrusion -Z) 0 at x=-50.
count_crossings now takes bulges= (per-chain DXF bulge lists, zero-padded)
and tests every bulged edge as its exact arc through the new
segment_arc_crossings — circle/segment intersection restricted to the
sweep — with the same junction rule as the straight case: a hit within
_EPS of the segment's ends, of the arc's own two ends, or a tangent, is
not a crossing. Nothing along the sweep is a vertex any more. The arc
parametrisation is factored into _arc_of_bulge and shared with
flatten_bulges, which keeps its promised signature and its ezdxf pin but
no longer feeds the crossing count. draw_line passes the vertices and
bulges through unflattened.
Pinned in tests: the apex case on the semicircle (x=50, y 20->60), the
r=5 jump at x=50 / 50.3 / 49 on +Z and -Z frames, the junction cases
(T-touch on the arc, through the arc's endpoint, chord side, tangent
along the apex, in-and-out at y=4.9 counts 2), and 4x400 seeded random
segment/arc pairs against ezdxf's ConstructionArc.intersect_line (a
20 000-case run in the worktree found 0 mismatches). The eight new
assertions fail on the flattened rule and pass on the exact one.
Headless finding, headless evidence; no new ActiveX call was written, so
the shared live AutoCAD was not touched.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
