OpenZL decoder, vendored for the verify-bundle guest

Heimdall is a defensive sandbox. This directory holds the C the guest compiles into its wasm32 module so it can read OpenZL-compressed znippy members (feature openzl, on by default). See docs/OPENZL-WASM.md for why and how.

Provenance

Copied from the published crate openzl-sys-rs 0.4.1+openzl.0.3.0 (crates.io, the exact library Holger and znippy link), whose openzl/VENDOR.md pins:

Licences: src/LICENSE (OpenZL, BSD-3-Clause), src/deps/zstd/LICENSE (BSD-3-Clause), src/deps/lz4/LICENSE (BSD-2-Clause).

What is here

• c-files.txt — the 115 translation units wasm-ld --trace pulls in for ZL_getDecompressedSize + ZL_decompress (decoder graph, codecs, the zstd and lz4 decompressors; no compressor except fse/compress/hist.c, which a decoder references).
• h-files.txt — the 268 headers those include (clang -MM).
• wasm32.patch — the ONE change: OpenZL static-asserts a 64-bit size_t only to keep its heap-arena header (HeapMeta) a multiple of 16 bytes; on a 32-bit target the header is padded instead and the assert dropped.
• shim/hzl.c — Heimdall's own C: a scalar-only ABI over the two entry points, and the five libc symbols the decoder references besides memory functions (stdio logging and vsnprintf write nothing; abort traps).
• vendor.sh — re-creates src/ from the crate and applies the patch: openzl/vendor.sh ~/.cargo/registry/src/*/openzl-sys-rs-0.4.1+openzl.0.3.0 then git diff --stat openzl/src must be empty.

build.rs compiles src/ + shim/hzl.c with clang for wasm32 against wasi-libc's headers only (no wasi-libc object is linked). malloc & co. are the guest's Rust allocator (src/zl.rs); memcpy/memmove/memset come from Rust's compiler-builtins.