The gzip codec loop already returns distinct status values, but the C
wrapper still owned the status branch that selected the CLI failure path.
That kept a format-result policy in the implementation-bearing C file even
though the loop itself is Rust. Add a Rust diagnostic mapping for success,
initialization, deflate, finish, end, invalid projection, and unknown
statuses. C now branches on the Rust classification while retaining zlib
result values, EXM_THROW codes, and exact diagnostic strings. This keeps the
ABI and observable behavior unchanged and leaves unrelated source-exclusion
and zstd classification seams untouched.
Test Plan:
- Nightly rustfmt check on fileio_asyncio.rs -- passed.
- Targeted git diff checks -- passed.
- Capped GCC syntax-only compile of fileio.c with codec defines -- passed.
- Focused Rust mapping tests were added; Cargo/tests were not run per the
task's OOM constraint.
ddidderr
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