The Rust-owned frame-progression ring scan consumes ZSTDMT_jobProjection
through ZSTDMT_projectJob. That callback previously copied counters under
job_mutex but read source and prefix metadata after unlocking. Keep the
complete projection in one mutex-protected snapshot, matching the original
ZSTDMT_getFrameProgression access pattern without moving descriptor or
synchronization ownership out of C.
Test Plan:
- `rustfmt --check --edition 2021 rust/src/zstdmt_compress.rs` -- passed.
- `git diff --check` and `git diff --cached --check` -- passed.
- Static inspection only; no cargo, make, native binaries, tests, fuzzers,
or heavyweight commands were run.
ddidderr
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