generateConductorPath()'s cas "3"/"4" branches each insert a two-point
bridge along one axis, at a coordinate on the other axis computed as
the midpoint of depart/arrivee and then snapped to the routing grid by
a loop that walks it strictly downward until it divides evenly.
When depart and arrivee already agree on the axis the bridge would run
along, no bridge is needed at all -- the midpoint starts on the
correct, already-shared value. But the snap can still walk it off that
value, or, when it happens to already sit on the grid, the two bridge
points just duplicate depart and arrivee outright. Either way the
conductor renders with an unnecessary out-and-back excursion or a
small looping detour at a join that needed neither.
Fix: skip the bridge in exactly that degenerate case, per branch, on
the axis that branch actually bridges on. descendant and montant are
not mirror images of each other in which axis each cas guards on --
each site says so.
Verified against the report's own canonical reproduction
(qet_bug_repro_resaved.qet from the linked gist): 1 self-retracing
path -> 0. Full corpus of 24 shipped example projects (stored
segments, as shipped, not regenerated): 74 -> 65 self-retracing
conductor paths, zero regressions -- only two files changed, both
improved.
One disclosed trade-off, found while checking for regressions: in
schema_unifilaire_voltaique2.qet, 8 terminal pairs closer together
than twice the extension length (docked stubs already cross before
any bridge is considered) go from an existing small rectangular-loop
artifact to a straight out-and-back retrace covering the full gap --
same count of defective paths (8 -> 8), a different shape, still no
connectivity change either way. Not chased further; a real fix for
that narrower "crossed stubs" case is a separate piece of work.
The shipped affuteuse_250h.qet's own 12 self-retracing paths (verified
by stripping all 185 stored <segment> elements and forcing full
regeneration) are unchanged by this fix -- they are a structurally
different point-count signature (a 4-point back-and-forth reachable
from cas "1"/"2", not the cas "3"/"4" grid-snap bridge this fixes),
consistent with what the issue thread already flagged as a separate,
undiagnosed mechanism.
Refs #734 (own root-cause comment, 2026-08-13).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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