A package internal to multistockfish.

It provides only the C++ dynamic library interface to Stockfish, and not the dart bindings.

This is Stockfish 19 built with the p_hm ("simple mirrored piece square") feature set in place of upstream's, which shrinks the evaluation network from ~94MB to ~1.1MB. The net is compiled into the library, so this flavour needs no download to evaluate — unlike multistockfish_chess, which is the same engine version with upstream's full-size net left out of the binary.

See UPDATING.md for how the vendored engine is patched and refreshed.