Follow-up: native 15:21 Alpine frames

All three actual frames in Docs/QA/20260915-152158-campaign were inspected. They remain visually rejected. The sky is lighter, but ground is ochre, the massif has little apparent photographic structure and forest cards are conspicuous. No material tint or shader configuration was changed during this diagnostic follow-up.

Confirmed source/import state

• The retained summer material has three layers: triplanar 0/1, planar 2, planar blend mask, no main-layer influence. Runtime confirms 4096-pixel orthophoto and a Repeat base sampler.
• The blend-mask PNG is linear RGBA, trilinear Clamp. The native HDRP 17.3 ComputeMaskWeights maps A→0, R→1, G→2, B→3 and consumes top-layer opacity first. With three layers, blue cannot introduce snow. Our channels match this ordering.
• The layer 0 and 1 albedo source images are sRGB Repeat, not mistakenly imported linear or clamped. Source means are Meadow (151.02,131.34,89.12) and ForestGround (106.28,89.80,67.67). Their actual pixels are brown/ochre leaf litter. They cannot supply the green summer meadow/woodland appearance with white multipliers; this is a source-selection error, independent of post-processing.
• At the fixed hero point (-3311.97,3494.55), geographic UV=(0.22400,0.52329), mask RGBA=(0,255,103,255), orthophoto pixel RGB=(161,154,126). At (-2700,3100), UV=(0.27500,0.48571), mask=(0,244,125,255), orthophoto=(115,113,92). At (-3400,2800), mask G=253 and orthophoto=(158,151,123). These are concrete targets for the parent task's native albedo/UV debug view. Source coordinates, orientation and layer indices check out; this does not by itself prove the final GPU sampling result.

Forest scale mismatch

The terrain shows a photographed forest floor underneath distant crown cards. Since distant cards deliberately cast no shadows, the kilometre-scale slope lacks the darkness and canopy pattern of a forest mass. A near-floor/far-canopy treatment is needed after the parent task's native material diagnosis. Increasing tree count or tinting the entire landscape would not establish whether shader sampling is correct.

Bounded alternative-source check

Two unmodified CC0 publisher archives were downloaded and inspected outside Assets, under ArtSource/Alps/SourceAssets/MeadowCandidates:

• ambientCG Grass001: darker dense green ground, mean source sRGB (68.14,91.52,40.34), documented procedural material, approximately 1.4 m physical width.
• ambientCG Grass005: brighter summer-green grass, mean source sRGB (101.45,131.84,43.64), documented procedural material with bitmap elements.

They are not described as photogrammetry. Original colour/normal/roughness/AO files and archive hashes are preserved in source-manifest.json; neither source is integrated yet. ambientCG's official licence explicitly permits redistribution in games under CC0. The native material debug pass remains the next dependency before any live material changes.