using: :nounzip formulas fail with misleading "store corruption: invalid gzip header" #442

Summary

Formulas whose url points to a raw, uncompressed binary (using: :nounzip) cannot be installed. The downloaded file is saved as source.tar.gz and unconditionally run through tar/gzip extraction, producing a misleading store-corruption error:

==> Installing can1357/tap/omp...
==> Resolving dependencies (1 packages)...
    • omp 18.8.6
==> Downloading and installing formulas...

Note: This package can't be installed with zerobrew.
      Error: store corruption: failed to read archive entry: invalid gzip header

      Try installing with Homebrew instead:
      brew install can1357/tap/omp

Environment

• zerobrew 0.4.0, macOS arm64
• zb doctor reports ✓ No issues found — the store is not actually corrupted

Reproduction

zb install can1357/tap/omp -v

omp 18.8.6 from can1357/tap declares:

on_macos do
  on_arm do
    url "https://github.com/can1357/oh-my-pi/releases/download/v#{version}/omp-darwin-arm64",
        using: :nounzip
    sha256 "31faa0ee8420a13a783f4ca56d98f974e4a9f9081d269057a099f7eb618d1133"
  end
end

Evidence that the download itself is fine

• /opt/zerobrew/tmp/build/omp/source.tar.gz is 203 MB and is a Mach-O 64-bit arm64 executable (magic bytes cf fa ed fe), not an archive
• Its sha256 (31faa0ee…d1133) exactly matches the formula's declared checksum
• Every attempt fails identically after ~1m20s (the download time), i.e. it deterministically fails at extraction, after a successful download

Root cause

1. zb_io/src/build/source.rs — non-bottle formulas always download the URL to source.tar.gz and call extract_tarball; the formula's using: annotation is ignored (there is no nounzip handling anywhere in the codebase).
2. zb_io/src/extraction/extract.rs — detect_compression() only recognises gzip/xz/zstd/zip magic bytes; anything else falls into CompressionFormat::Unknown, whose handler is // Try gzip as fallback → GzDecoder::new(reader) on a non-gzip stream → invalid gzip header.
3. The store corruption: prefix makes a supported-format gap look like data corruption.

Expected behavior

Either:

• Support using: :nounzip: skip archive extraction, place the downloaded file directly into the source dir / keg and mark it executable; or
• Fail clearly: detect the non-archive case and return an explicit "unsupported raw binary download; install with Homebrew" message instead of a store-corruption error.

Scope

Not specific to this tap: any formula that downloads a bare executable via using: :nounzip (increasingly common for tools shipping single-file release binaries) will hit the same failure. Related prior art: #250 (unsupported cask binary artifact shape).