fix(examples): redesign gltf-export-roundtrip as one crate under its re-imported wire cage

[TMHSDigital]

What changed and why

The review found two identical crates with small floor text reading AUTHORED / ROUND-TRIP. That is the identical-copies failure mode: because a pass means the two crates look alike, there is nothing for the eye to find.

The hero is now one crate:

• The solid crate is the authored one.
• Laid over it is the actual re-imported mesh (the file's own triangles). It is drawn as a thin amber wire cage through a render-only Weld + Wireframe display stack and masked to the right of a vertical cut.
• Neither object is moved. Both keep the identity transform that check 13 proves, and the camera does the turning.
• The cage lands on every bevel, rivet and vent slat only because the importer undid the export_yup bake exactly and the file carried the evaluated (beveled) mesh.
• If the axis conversion broke, the cage would sit a quarter turn off the crate. If the modifier contract broke, it would trace square corners.
• The floor text is removed.

The crate itself has been upgraded:

• It grows from 35 to 43 box shells: vent slats under each carry handle, and stiffening ribs across the lid.
• The trim is a lighter gunmetal and the paint a warmer olive.
• The authored copy gets noise-mottled paint and trim, on the render path only.

The render path now also runs gallery_asset_quality on the authored crate, with its exit 11 remapped to 23. The bevel is baked into the display mesh first, because the edge90 measure reads Object.data, which is still the square cage.

Also in this PR:

• read_gltf now opens its JSON with encoding="utf-8".
• scripts/asset_sheet.py gains a gltf-export-roundtrip SELECT row (^Crate\.Authored$).

Evidence

• Contact sheet: docs/gallery/contact-sheets/gltf-export-roundtrip-contact-sheet.webp
• Asset sheet: docs/gallery/asset-sheets/gltf-export-roundtrip.webp

Framing: fill x=0.556, y=0.828 (band 0.70-0.90). Margins: left 0.222, right 0.222, bottom 0.078, top 0.094. framing_ok on 5.2.1 and 4.5.11.

Asset floors (authored crate): no default names, 3 materials (the floor applies only when parts >= 2; parts = 1), edge90 = 0.000. aq_ok.

Contact sheet, per criterion:

Criterion	Candidate	Calibration	Verdict
Mean luminance	0.229	armature-bend 0.279, damped-track-aim 0.151, bmesh-gear 0.236	PASS, inside the range
Stage darkness	0.166	0.145-0.213	PASS
Wedge warmth	+0.364	warm, like damped-track-aim +0.277 and bmesh-gear +0.303	PASS
Saturation	0.170	0.144-0.250	PASS
Thumbnail legibility	At card size, the amber cage over the right half of the crate reads immediately	-	PASS

Asset sheet verdict: PASS, not the least-designed object in the lineup. The crate has more modeled parts and edge treatment than the hydrant and the well, though it is boxier than the drone and the shelf.

A note on the asset-sheet tool: its fit-to-extent camera frames the crate tightly, and the crate touches the edge of its panel. That is the shared tool's framing. The example itself is not affected.

Hero drift (measure_hero_drift.py --only): mean_abs 0.00834, verdict matches.

Check runs (check-only path)

Binary	Reported version	Check	--no-yup falsifier
E:\Blender-Developer-Tools\.scratch\blender-5.2.1-windows-x64\blender.exe	Blender 5.2.1 LTS	exit 0	exit 9 (bbox deviates 8.700e-01)
E:\Blender-Developer-Tools\.scratch\blender-5.1.2-windows-x64\blender.exe	Blender 5.1.2	exit 0	exit 9 (8.700e-01)
E:\Blender-Developer-Tools\.scratch\blender-4.5.11-windows-x64\blender.exe	Blender 4.5.11 LTS	exit 0	exit 9 (8.700e-01)

All three versions give the same measurements: verts=344, eval_loops=9288=disk_verts, tris=4644, pos_err 0.00e+00, nrm_err 6.35e-05, uv_err 3.11e-07. The render path also passes on 4.5.11 (EEVEE Next) with identical framing numbers.

Falsifiers

• --no-yup (the existing contract falsifier): exit 9 on all three binaries, as shown above.
• Asset-quality call site (new, exit 23): a temporary probe copy skipped the bevel bake. Result: aq_edge90 frac=1.000 (516/516) FAIL, exit 23. The probe was then deleted.
• Visual witness: a temporary probe copy re-applied the missing quarter turn (rotation_euler.x = 90 deg) to the imported object before rendering.
  • With the framing gate left on, it exits 22 (bottom margin 0.000).
  • With the gate bypassed, the rendered cage falls through the floor, away from the solid crate.
  • The probe was then deleted.

Proven by live run vs established by inspection

Proven by live run:

• Check and --no-yup on 5.2.1, 5.1.2 and 4.5.11
• Render path, framing and asset-quality gates on 5.2.1 and 4.5.11
• Both probes above
• render_hero.py, contact_sheet.py, asset_sheet.py and measure_hero_drift.py on 5.2.1
• build_gallery.py, after the rebase onto origin/main. The generated <img alt> in docs/gallery/index.html and docs/gallery/gltf-export-roundtrip/index.html was read.

Established by inspection only:

• 5.1.2 render-path output (only the check-only path was run there)
• CI smoke on 5.2 and 4.5, which is pending on this PR

🤖 Generated with Claude Code