The Anchor Point tool drags any segment of a selected blend's spine into
a curve, straight ones too, and Direct Selection reshapes a curved spine
segment as it does a path's (a straight one it leaves, as on paths). Both
run the new `object.blend.spine.reshapeSegment`, which bends the segment
with the same math as `path.reshapeSegment`, now shared as
`SubPath::bend_segment`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>