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Delta engines
Single-file binary deltas live in internal/delta. The server must build with CGO_ENABLED=1 and a C++ toolchain (Windows MinGW g++ / Linux g++ or clang++ / macOS Xcode clang++). It does not exec hdiffz/hpatchz from PATH at runtime. The Go SDK stays CGO_ENABLED=0; see the SDK pages.
| Algorithm | Magic | Notes |
|---|---|---|
| hdiffpatch (CGO) | HDIFF13& | New diffs are uncompressed official HDIFF13; DescribeAvailable is cgo |
| Historical hdiffpatch | KVDIFFHP1 | Patch-only; not official .hdiff |
| bsdiff | BSDIFF40 | pure-go |
| xdelta3 / VCDIFF | D6 C3 C4 | RFC 3284 binary magic, not ASCII; pure-go |
Patch dispatches on magic; never cross-decode. Unknown admin algo → DELTA_ALGO_UNSUPPORTED. Admin POST .../artifacts/delta enqueues a Job. HTTP handlers must not import archive/zip.
Official darwin/* binaries must be CGO-built on a macOS host (darwin/arm64 natively, darwin/amd64 same-host clang -arch x86_64); never a Linux→darwin CGO cross without an Apple SDK. The GitHub release workflow builds both on a pinned macOS runner (macos-15). GitHub is the only forge, so no target is ever skipped for lack of a host: if an artifact is missing, the packaging job fails instead of fabricating a file.