test(format): tar/cpio/ar/ISO producer corpora and metadata round trips [RM-304]

[P4suta]

RM-304 / DEV-110 — tar/cpio/ar/ISO producer-specific corpora and metadata round trips

Lifts the RM-301 interoperability harness from content-only evidence to metadata fidelity for the sequential and disc formats. Test/corpus slice only — no src/ runtime change (tar/cpio/ar/ISO already encode/decode their metadata; this proves it end-to-end against independent producers/consumers).

Harness extension (tests/common/mod.rs, additive)

The content-only EntryShape path is untouched. Added: read_seq_with_arca (sequential ArchiveReader — the seek reader only indexes ZIP/ISO); MetaShape (preserves the real entry kind — Symlink/Hardlink no longer fold to File — plus typed mode/uid/gid/mtime/link-target); read_meta_seq_with_arca / read_meta_seek_with_arca; assert_producers_agree_seq. Producers/consumers stay bare fn pointers, so no-dyn and forbid(unsafe) hold.

Per-format coverage (honest scope)

• tar — 3 producers (arca, tar@0.4, first-party raw ustar builder) × 2 consumers (arca seq, tar@0.4); mode/uid/gid/mtime + symlink fidelity.
• cpio — 3 producers (arca newc, raw newc, raw odc — genuinely distinct on-disk framings) × 2 consumers (arca, first-party raw newc parser); mode/uid/gid/mtime + typed hardlink pair. No pure-Rust cpio producer crate exists, so the 3rd producer is a second first-party builder in a different dialect (documented in PROVENANCE).
• ar — 3 producers (arca, ar@0.9, raw !<arch> builder) × 2 consumers (arca, ar@0.9); mode/uid/gid/mtime (ar is flat regular-files-only).
• ISO — arca self round trip + external xorriso/genisoimage/mkisofs producer (graceful skip); Rock Ridge PX/TF/SL fidelity (mode/uid/gid/mtime + symlink) via the seek reader. No pure-Rust independent ISO reader exists on all targets.

Notes

• New test-only dev-deps (no effect on the shipped crate's portable/C-free profile): tar = "0.4", ar = "0.9".
• Per-format tests/fixtures/*/PROVENANCE.md register each producer and the ISO external-tool escape hatch.
• The cpio/ar/ISO tests were authored via parallel subagents against a tar reference, then reviewed and verified. just ci passed locally.

🤖 Generated with Claude Code