Constant BUNDLE_LAYOUT 

pub const BUNDLE_LAYOUT: &str = "\
rust-dev-rhel8-<rustc-ver>.znippy
├── manifest/
│   ├── bundle.json            # rustc/cargo version, host triple, source-URL provenance
│   ├── toolchain.pins.json    # per-payload sha256 + blake3 (the \"pinned like the kernel\" table)
│   └── vendor.lock            # exact crate set = a copy of the source Cargo.lock
├── toolchain/                 # the standalone (rustup-dist) toolchain, UNPACKED into the tree
│   ├── bin/                   # rustc, cargo, rustdoc, rust-lld, …
│   ├── lib/                   # librustc driver .so's, std .rlibs
│   └── lib/rustlib/<triple>/  # the rust-std for the target
├── vendor/                    # `cargo vendor` output — the \"basic crates\" set
│   └── <crate>-<ver>/…        # already-compressed .crate contents expanded to source
└── cargo-config/
    └── config.toml            # source-replacement → vendor/, offline hard-on";

The canonical bundle layout, printed by the layout subcommand and mirrored by the classifier in member.