Scene Setup & Hygiene

The execution model and verification steps are in blender-core.

Procedure

1. Run scripts/scene_audit.py (add --fix purge scale paths only on files you own). It reports units, unapplied/negative scale, default names, objects in the scene root, missing images, orphans and far-off origins.
2. Set units: Metric, Unit Scale 1.0, Length meters. Keep 1.0 even for Unreal/Roblox, because exporters handle the conversion (see blender-export-pipelines).
3. Build the collection layout (below). Every object must be in a named collection, never the scene root.
4. Name everything with the conventions below. Rename after every duplicate or join so no .001 suffixes remain.
5. Set origins: props at the bottom-center (they sit on the ground at Z=0), characters at world origin between the feet, doors/hinges at the pivot.
6. Apply rotation and scale on meshes (Ctrl+A). Keep location unless the asset should export at the origin.
7. Re-run the audit. It's done when issues is empty or every remaining issue is intentional and explained.

Collection layout (one asset per .blend, or one collection per asset)

ASSET_Crate
├── Crate_high      # sculpt / subdiv source (exclude from export)
├── Crate_low       # game mesh(es) SM_Crate, SM_Crate_LOD1..
├── Crate_bake      # cages, bake helpers
├── Crate_collision # UCX_SM_Crate_00 (UE) / Crate-col (Godot)
└── Crate_ref       # reference images/blockout (hide_render)

Use Collection Exporters (4.2+) to define the export once per collection, then re-export with one call:

with bpy.context.temp_override(collection=col):
    bpy.ops.collection.exporter_add(name="IO_FH_gltf2")
ex = col.exporters[-1]; ex.export_properties.filepath = "//export/SM_Crate.glb"
with bpy.context.temp_override(collection=col):
    bpy.ops.collection.exporter_export(index=len(col.exporters) - 1)

bpy.ops.wm.collection_export_all() re-runs every collection exporter.