docs(audits): PathBuf and Arc<Path> RSS overhead per FileEntry#3704
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Adds an audit for task #1048 quantifying the path-storage portion of the 100K-files RSS gap (87.5 vs 7.4 MB at v0.5; 42.6 vs 7.9 MB current per the flist-memory baseline). Per-entry breakdown of `name: PathBuf` (24 B inline + heap with capacity slack) and `dirname: Arc<Path>` (16 B inline + 16 B `ArcInner` header), comparison to upstream's pool-allocated `struct file_struct` + `lastdir` cache from `flist.c`/`rsync.h`, and a test/benchmark plan reusing the existing file-entry memory benchmark. Recommends an `Arc<[u8]>` per-flist arena with `(offset, len)` slice fields as the natural shape for #1050, with `Box<[u8]>` post-sort as the smaller mechanical fallback.
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Adds an audit for task #1048 quantifying the path-storage portion of the 100K-files RSS gap (87.5 vs 7.4 MB at v0.5; 42.6 vs 7.9 MB current per the flist-memory baseline). Per-entry breakdown of `name: PathBuf` (24 B inline + heap with capacity slack) and `dirname: Arc<Path>` (16 B inline + 16 B `ArcInner` header), comparison to upstream's pool-allocated `struct file_struct` + `lastdir` cache from `flist.c`/`rsync.h`, and a test/benchmark plan reusing the existing file-entry memory benchmark. Recommends an `Arc<[u8]>` per-flist arena with `(offset, len)` slice fields as the natural shape for #1050, with `Box<[u8]>` post-sort as the smaller mechanical fallback.
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Summary
Arc<[u8]>per-flist arena with(offset, len)slice fields as the natural Rust port of upstream's pool layout (flist.c:1018-1027,rsync.h:801-830), withBox<[u8]>post-sort as the smaller mechanical fallback.crates/protocol/benches/file_entry_memory.rs(Fix merge directive helpers in CLI filter parsing #1037) and the empirical 100K/1M numbers indocs/benchmarks/flist-memory-baseline-2026-05-01.md.Test plan
crates/protocol/src/flist/entry/{core,extras,constructors,accessors,tests}.rsandcrates/protocol/src/flist/intern.rs.target/interop/upstream-src/rsync-3.4.1/{flist.c,rsync.h,compat.c}.