The layout file: .steamhelper.json

Every mods folder uses the RimWorld layout, which is built into the program: each mod folder has About/About.xml (name, modVersion, supportedVersions, modDependencies), an optional About/Manifest.xml whose <version> wins, About/Changelog.txt (one entry per version, Add Changenote style), About/PublishedFileId.txt, About/Preview.png, an optional About/steam_description.txt and an optional Gallery folder. Builds in Assemblies and */Assemblies are packaged even when git ignores them.

.steamhelper.json in the repo root records only the layout's name and the folder's Leave these out patterns (LeaveOut). Anything else in it is ignored. A file written by an earlier version for another layout (Generic, Custom, Paradox, Golf With Your Friends) is not used: the window and Check setup say so, and the RimWorld layout is used instead.