How to prevent textures from being removed when only referenced by an extension not a material

[MAG-AdrianMeredith]

Hello all, I'm looking to improve my plugin for a custom extension EPIC_lightmap_textures. Unfortunately the way its made is making life difficult. Essentially what this does is adds a new property onto a node that references a set of lightmaps. The problem here is that these properties are a NODE extension, not a material one. As a result gltf-transform very unhelpfully strips them out, despite not asking it to (using the copy command with --config arg to enable the extension).
Previously I worked around this by setting the texture to the occlusion slot but that caused a ton of issues. Instead I'm trying as close as possible to align it with how the "transmission" extension works just in a different part of the graph.

By the end of the "read" function my context has nodes with the extension property filled, 4 textureInfos, and one texture entry.
By the start of the "write" they've all been stripped out.... why!?