uefn-materials (MVP experimental, B8)

Source: Claude/docs/mcp/materials.md, recipes.json, SKILLS-PROPOSAL.md B8. Read first: skills uefn-mcp-lab-guard (guard rules, lab mount) and uefn-create-use-remove-one-script (create, use and remove in ONE script).

Rules

• Paths in GUID form: lab mount /09e4e8d3-83f9-4ee0-9777-072ed3984380/root_ai_lab (never /root_ai_lab). Run from PowerShell (Git Bash path-converts the value).
• The guard is never bypassed. A refusal is reported verbatim to the owner, not worked around. If a recipe fails: report the exact error and STOP.
• Must NOT: duplicate engine materials into the lab (refused); leave Mat_* assets (clean up with AssetTools/delete).

Recipes tool-ok or proven (recipes.json)

MaterialTools (editor_toolset.toolsets.material.MaterialTools): create_material {folder_path, asset_name}, add_expression, connect_expressions, connect_to_output, get_property_input, recompile, get_statistics, diff_material. MaterialInstanceTools (editor_toolset.toolsets.material_instance.MaterialInstanceTools): create, list_parameters, set_scalar_parameter, set_vector_parameter, set_static_switch_parameter, set_texture_parameter, set_parent (cleanup: set_parent back to the original), clear_parameters, get_scalar_parameter. Cleanup of created assets: AssetTools/delete {path: package path without .Name}.

Traps

• ObjectTools/set_properties on a material takes values as a JSON TEXT string. B-002: the guard does not inspect a string values, so put only lab objects and plain numbers/colors in it, never a class or asset path of a Verse script.
• Float readback 0.9 = 0.8999999761581421. One bad key in the values JSON fails the whole set.
• Each new Material adds shader compile time: prefer instances.
• get_referencing_materials returns [{}] without a path. set_parameter_override false returns the parent value. No MPC edit tool (asset only). No blend-mode tool (use set_properties, untried).

Documented fix: drone (materials.md "Drone fix log", 2026-10-16)

Symptom: log Material ... missing usage flag SkeletalMesh! Default Material will be used in game on a skeletal mesh (mech-drone, slots Fire/Robot); instances had parent FBX Interchange phong with empty textureParameterValues and all *MapWeight 0. Fix: (1) create lab materials with ObjectTools/set_properties {values: '{"bUsedWithSkeletalMesh": true}'} (key WITH the b prefix; usedWithSkeletalMesh fails); (2) wire textures (BaseColor, Normal, Gloss->OneMinus->Roughness, AO R, Emissive) and recompile; (3) MaterialInstanceTools/set_parent of each slot instance to the new material, then save_assets. Revert: set_parent back to the Interchange phong parent (original values untouched). Status: recompile ok (217 / 158 instructions); bUsedWithSkeletalMesh reads true; NOT verified visually and no fresh in-game log line after the fix.

To try (not verified)

• recipe/apply_material_instance_to_actor (ONE script): status unverified in recipes.json.
• MaterialInstanceTools/set_parent#drone_skeletal_fix, recipe/apply_lab_mi_to_owner_skeletal_actor: unverified (no visual check; touches assets outside the lab, needs the guard roots).
• StaticMeshTools/set_material: not run (only an engine mesh available).