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SomaStacks Inc 9

Full USD→material→texture chain audit (independent verification + experiments)

Follow-up to the repro-server "missing texture" report. Every claim below was verified by
traversal (usd-core 26.8) or by a controlled RTX render experiment (IsaacSim 5.0.0 + isaaclab
2.2.0, headless RT). Artifacts: WUJI_SimBench reports/05_benchmarks_infra/palm_logo_texture_audit/.

1. This PR's change — independently verified correct

Attribute-level diff main vs refs/pr/14: 16522 attributes on both sides, 0 added, 0
removed, exactly 4 values changed (left/right palm OmniPBR.inputs:diffuse_texture +
DiffuseTexture.inputs:file, absolute → USD-anchored relative). The relative anchor resolves.

2. The "missing file" symptom, explained

fused/{left,right,left_simplified,right_simplified}/textures/wuji_logo_placeholder.png are
all present on main and byte-identical (md5 49d9b9d7…, HF == local). Nothing is missing
from the repo. On a fresh machine the robot USD's absolute /home/franka/... reference is
unresolvable AND invisible to per-file asset fetchers, so the texture is never downloaded and
UsdToMdl logs it as not-found — a path bug masquerading as a missing file. This PR is the fix
for that layer.

3. Reference-chain classification (the three states)

Delivery robot USD (robots/tianji_wuji/tianji_wuji.usd):

• actually rendering: BlackGlove (palm mesh_base), SilverNail (mesh_seat, rootPlugs) — solid colors, no texture;
• referenced by a material that is bound to nothing: wuji_logo_placeholder.png ×2 — left/right_palm_link_Material are orphans; stage has 0 GeomSubsets and 0 of 346 meshes carry primvars:st (the fuse/graft bake split subset-materials into per-material meshes and dropped both the palm's logo-material assignment and every UV);
• present but unreferenced (by the robot USD): the two *_simplified texture copies (only their own wujihand.usd reference them).

Source fused/*/wujihand.usd (all 4 variants): material bound ✓, dual MDL+preview networks
wired ✓, st authored ✓ — but st has 25170 entries against 27312 face-verts. Hydra:
"corrupted data in primvar 'st': buffer size 25170 doesn't match expected size 27312" → the
authored UVs are discarded. The logo has never rendered anywhere, including the source assets.

4. Experiments (controlled, same zoom)

1. Checker swap: replacing the PNG with a magenta/yellow checker turns the palm pink (the
   whole-texture mip average via the degenerate-UV fallback) — texture reachable, authored UVs lost.
   The real texture's average is dark grey, which is why the defect is invisible in normal renders.
2. Length pad: padding st to 27312 (background texel) makes red appear at the same camera
   distance where the shipped asset shows 0 red pixels — the length mismatch is the gate. But it
   renders as fragments, not letters: the mesh gained 714 triangles after the UVs were authored
   (jointSeat bake), so the surviving st values are misaligned. Padding is not a shippable fix.
3. Control: a minimal stage (OmniPBR + faceVarying st + relative texture) renders correctly —
   the render stack is fine; the defect is in the asset data.

5. Verdict & blockers, in order

The texture is one placeholder doubling as glove+logo via palette UVs (98.9% of face-verts
pinned to the dark texel; a small wrist-area face patch pinned to the red letters). For the logo
to actually render in the delivery robot USD:

1. material binding — palm logo material is orphaned (graft assigned mesh_base to BlackGlove);
2. primvars:st missing on every robot mesh;
3. upstream: the source st itself is stale vs the current topology (25170 ≠ 27312) and must be
   re-authored by the asset factory — no downstream repair can reconstruct the mapping;
4. path config — fixed by this PR (necessary, not sufficient).
   GeomSubsets are not required (palette UVs need none).

Recommendation: merge this PR as-is (it fixes resolvability/fetchability and kills the
UsdToMdl noise). The logo itself needs a factory re-export of the palm UVs against the current
mesh, then a follow-up that rebinds the palm material and restores st through the graft.