The per-vertex `bulges` list was handed out in the entity's own frame next
to `points` that had been translated to WCS. A mirrored LWPOLYLINE
(extrusion / Normal -Z, what `entity_mirror` produces) is a reflection,
which reverses every arc's sense, so the reader tested endpoints against
the arc's mirror image: a line ending on the true apex dangled, a line
ending on empty paper made a junction, and `length` (frame-invariant)
said nothing. Both engines had it — ezdxf emitted `get_points("xyb")`
raw, COM returned `GetBulge` raw after reflecting `Coordinates`.
`ocs.wcs_bulge(extrusion, bulge)` now negates the sign for a left-handed
frame (the same rule `wcs_arc_angles` applies to an ARC's endpoints) and
both `_entity_info` paths route bulges through it whenever they translate
the points. Fenced by an end-to-end mirrored-pipe graph test, the COM
`_entity_info` fake with Normal -Z, and a boundary-level OCS test.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
Two reader defects, both about trusting a derived number over the drawing.
Stale junctions: endpoints were resolved before a foreign line's membership
was decided, so a P&ID line ending on a foreign line that was then discarded
(it touched no node) kept `{"junction": "J1"}` while `junctions` was empty
and `stats.dangling` was one short. Node attachment now runs first for every
edge, the foreign lines that attach are admitted, and only then are junctions
and dangling ends resolved over the edges actually in the graph.
Chord length: `length` was a chord walk over the vertices, 12.5% short on a
semicircular crossing jump with no field saying so, and junction detection
tested the chord too, so a line ending on the arc dangled. Both engines now
report per-vertex `bulges` next to `points` (COM asks GetBulge only when
`Length` exceeds the chord walk, since an arc is always longer than its
chord); the reader takes the engine's bulge-aware `length` and tests
endpoints against the arc. The chord sum survives only for an engine that
reports no length, and is then labelled `length_approximate`.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
