Use the existing bounded thin-header decoder for loaded and embedded FAT
identities, thin-image resolution, and both prepared-copy readback paths.
Preserve raw unsigned CPU/subtype facts and endian handling.
Keep the initial eight-byte dispatch, FAT framing, selection and ranking,
source digests, error ordering, cancellation and cleanup authority local.
Validation: Mach-O container, Hopper image/copy lifecycle and file-offset close
boundary suites passed. No attached Hopper GUI or real-provider run performed.