Root cause confirmed (decomp cross-check wf_3c1120c4-a04 + live apparatus): the
outdoor stairs are a continuous coplanar 38.7-degree ramp of stacked step-box
objects; at a seam the grounded forward move loses contact_plane_valid, the
step-down recovery can't reach the coplanar (at-level) continuation, and
EdgeSlide/PrecipiceSlide fabricates a horizontal (0,1,0) sliding normal that
absorbs the up-stairs motion (the #137/TS-4 family). Fabrication math, the
SetSlidingNormal Z-zero, and the multi-object search are all verified faithful;
the divergence is upstream (retail keeps contact_plane_valid, pc 273244).
Approach A: restore retail's grounded forward-move retention so the fragile
step-down recovery isn't needed at seams. Exact retention-loss line pinned by a
dat-backed replay test (the #137 method), not guessed. Alternatives B/C recorded.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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