Move the transparent ZSTD_CCtx_init_compressStream2 initialization policy into
Rust. Rust now owns the ordered local-dictionary, prefix, parameter-resolution,
pledged-size, worker-selection, and ordinary-buffering decisions through a
scalar projection and explicit callbacks.
Keep the private CCtx and parameter layouts, allocator and trace state, MT
context lifecycle, codec operations, reset behavior, and mutation details in C.
The C shim therefore remains the ABI and private-state boundary while the
high-level stream setup flow is testable in Rust without duplicating those
layouts.
Test Plan:
- cargo test --manifest-path rust/Cargo.toml --all-targets -- --test-threads=1
- cargo test --manifest-path rust/cli/Cargo.toml --all-targets -- --test-threads=1
- run the legacy Rust feature matrix and all six library/CLI clippy gates with
-D warnings
- run lib and program native rebuilds plus test-cli-tests,
test-rust-lib-smoke, and test-zstd with make -j1
- run fuzzer, zstream, and decode-corpus stress gates serially with
ulimit -v 41943040
Commit is intentionally unsigned because GPG pinentry hangs in this
non-interactive environment.