Command-line tool for sending and receiving nanomsg SP messages on any NNQ socket type (REQ/REP, PUB/SUB, PUSH/PULL, PAIR). Supports Ruby eval (-e/-E), script handlers (-r), the virtual `pipe` socket with optional Ractor parallelism, multiple formats (ASCII, msgpack, Marshal), and Zstd compression. Like nngcat from libnng, but with Ruby superpowers.

Wraps any NNQ::Socket with per-message Zstd compression, bounded decompression, in-band dictionary shipping, and sender-side dictionary training. No negotiation; both peers must wrap.