V3 deterministic Zstandard compression capability pack. By-value connector composition (service_kind=cli, no separate ingredient): one local zstd CLI ingredient exposes readiness, default compression, fast compression, decompression, and compressed-stream integrity testing. Fixed-function and reproducible: the executor materializes source files and owns the throwaway output directory, while zstd writes fixed output files that are captured as result.file_ref. Write-tier operations write only to an engine-managed output dir, read-tier testing returns only exit status, and recipes cannot pass arbitrary flags, dictionaries, recursive inputs, file lists, source-removal flags, shell wrappers, or caller-controlled output paths. Requires the zstd binary on PATH (Debian/Ubuntu: apt install zstd; macOS: brew install zstd). Local and no-egress.