MCP backend

Use when: Full surface texture coverage, sidewall UVs, back cap UVs, closed mesh UV coverage audits, texture fill validation, side/back turntable QA, replacing projected overlays with real surface materials.

Before the first Blender call, read ../text-to-blender/references/mcp-backends.md. Prefer official MCP for shared capabilities; preserve the selected backend for the whole task. Tool names in recipes are client/legacy examples: map them through that reference and its agent-host guide.

Closed Surface UV Coverage

This skill prevents a common false pass: a model looks textured from the front because it has a projected front image or curve overlays, but the closed surface has untextured back caps or plain sidewalls when viewed in a spin/turntable.

Failure modes to catch

• Back detail is only a floating plane or curve overlay, not a material/UV on the back surface.
• Sidewalls have procedural color only; no side UV island, generated/object coordinate material, or baked strip.
• A back projection covers only a center shape and leaves the actual silhouette/back mesh plain.
• Side/back QA uses front-biased frames and misses edge-on/back-on samples.
• Decorative HUD/aura is mistaken for surface texture coverage.

Required surface taxonomy

For extruded/logo-like assets, classify visible surfaces before look-dev:

1. front_cap — canonical front texture/decal.
2. back_cap — back texture, back linework, or baked/procedural fill mapped to the real back cap.
3. sidewall — depth surface connecting front/back, with its own UV parameterization or procedural material.
4. overlay_context — HUD/aura/circles; never counted as model surface coverage.

Workflow

1. Audit current coverage: list mesh material slots, UV layers, image texture nodes, and face counts for front/back/side material indices.
2. Reject overlay-only fixes: curves/planes may add rim accents, but they do not satisfy back/side fill unless the mesh surface beneath is also textured/materialized.
3. Create per-surface UVs:
   • front/back caps: project local X/Z to UV 0–1 or map into a back/front atlas rectangle;
   • sidewall: map perimeter arc length to U and depth/front-back coordinate to V;
   • if a clean side texture is unavailable, use a generated procedural side material plus baked glow/edge strip and document it.
4. Assign true surface materials: back cap and sidewall mesh faces must have material nodes, active UVs, and/or generated coordinates. Optional curves are accents only.
5. Validate turntable frames: sample front, 45°, side/edge-on, back-on, opposite 45°, and rest. Back and side frames must show surface fill, not just outlines.

Acceptance gates

• Back cap mesh faces have either an image/procedural material with a declared UV/generated coordinate policy, not only separate curves.
• Sidewall mesh faces have a sidewall material with UV/generated coordinates and visible depth treatment.
• Overlay/context collections are excluded from coverage counts.
• QA contact sheet includes back and edge-on frames.
• A surface_coverage_report.json states which surfaces are image-textured, procedural, baked, or intentionally plain.

Handoff

Use after geometry is locked and before final material/look/animation acceptance. It complements blender-uv-texturing and atlas-uv-fitting: those skills explain UV/material setup; this skill enforces complete visible-surface coverage.

Script

• scripts/surface_texture_coverage_audit.py audits selected mesh objects for UV layers, material image nodes, face material counts, and overlay-only warning patterns.