The Holtburg windmill (Setup 0x020003E5, cycle 0x0300061B) is a 60-frame
quarter turn that loops by 4-blade symmetry: frame 59 and frame 0 are the
same picture but 88.5 deg apart. BuildBlendedFrame wrapped the cyclic
node's next-frame index to frame 0, so the seam slerped 88.5 deg backwards
inside one 33 ms interval - the blades visibly flapped back every two
seconds.
Retail never blends animation frames at all: CPartArray::UpdateParts
(0x005190F0) applies get_part_frame(floor(frame_number)), holding every
authored frame for its interval and hard-cutting at the wrap. The
render-side blend now holds the boundary frame at BOTH ends of a node's
window - the same rule the #61 link-tail fix already applied to one-shot
nodes - so every seam is retail's cut while interior frames stay smooth
(the owner's choice over dropping the blend, 2026-08-23). Register row
AP-233 records the blend as the deviation it has been since the R1-P5
cutover.
Test: Advance_CyclicSeamHoldsLastFrameInsteadOfBlendingIntoFrame0 (fails
on the previous code at ~45 deg, passes held at 90 deg). Core 4,696/0,
App 6,068/0 hermetic (Release).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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