v0.3.0

v0.3.0 — three-platform SFX + codec-agnostic + --bin archive run

The first release with self-extracting binaries on all three platforms, a codec-agnostic container (zstd default, gzip via --gz), and AppImage-style archive run (--bin). Plus CI stability and a working crates.io publish path. 45 tests pass.

• Test coverage 32 → 45 (+13 regression guards): read-op independence
  (-l/-t/-d work without -c), CLI validation (-c w/o -o, -o w/o
  -c, no-args, missing-file), -z range (0/20 rejected), empty-file
  round-trip, payload-integrity (-t catches a corrupted payload byte via
  zstd's default content checksum), SFX runtime (stdin inheritance,
  stdout/stderr separation, truncated-trailer clean failure), and gzip-SFX
  rejected on macOS. PR #15.
• Build fix — Linux cargo build --release deadlock (#16):
  build_linux_stub recursed into cargo build -p upxz-stub against the same
  workspace target/ the parent release build was locking → the child blocked
  on the target-dir lock and build.rs never returned (63-min CI hang). Fixed by
  isolating the recursive build's CARGO_TARGET_DIR under OUT_DIR, mirroring
  the macOS/Windows branches that already did this.
• crates.io publish (#11, PR #17): build.rs now detects whether the SFX
  companion-crate sources are present. From a git checkout / cargo install --git the stubs compile (full SFX). From a stripped crates.io tarball (cargo
  drops nested-package subtrees) it emits empty placeholders + clear
  cargo:warnings — cargo publish succeeds and cargo install upxz gives a
  working runner/packer; upxz -c points to --git/releases.
• Integrity contract documented: -t / unpack / run are true integrity
  checks — zstd's default content checksum (xxhash32) is verified by libzstd on
  every decode path, including the no_std macOS loader. See mneme
  docs/upxz/integrity-check.md.

Feature detail:

• Windows SFX (upxz -c on Windows): a third platform for the
  self-extracting-binary feature. The Windows SFX layout mirrors the Linux
  stub ([stub][.upxz][trailer: u64 stub_size BE]); the upxz-winstub crate
  resolves its own path via GetModuleFileNameW, decompresses the .upxz
  payload (zstd and gzip — no size gate, unlike the macOS no_std
  loader), writes the restored PE to %TEMP%, and CreateProcessWs it with
  argv forwarded verbatim. No ad-hoc code-signing is required on Windows
  (unlike macOS AMFI). The in-memory NT-section route
  (NtCreateSection/NtCreateProcessEx) is documented but not compiled —
  windows-sys lacks NtCreateProcessEx, the resulting process has no
  initial thread/PEB, and it is the technique AV most aggressively flags; see
  winstub/src/main.rs and mneme docs/upxz/sfx-stub-windows.md. The
  temp-file path is the supported Windows mechanism.

• Status: code complete + cross-compile-verified to
  x86_64-pc-windows-gnu (cargo build --release --target x86_64-pc-windows-gnu succeeds, producing a valid PE32+ upxz.exe).
  Awaiting real-Windows runtime validation (develop host is macOS).
  Linux/macOS SFX branches are untouched (#[cfg]-isolated).

• Refs: mneme docs/upxz/sfx-stub-windows.md, docs/upxz/windows.md; PR #10.

• Codec-agnostic container (--gz): the magic byte at offset 5 now carries
  a codec id — 0 = zstd (default, fully backward-compatible), 1 = gzip. The
  runner / unpacker / list / test paths all dispatch on this byte, so one upxz
  binary handles both codecs. --gz on pack selects gzip; -z N clamps to the
  DEFLATE range 1..=9 (default 9). Without --gz, pack writes zstd (codec 0),
  identical to v0.2 — every existing .upxz still runs unchanged.

• Backends: gzip via flate2 with the pure-Rust miniz_oxide backend (no
  C libz, statically linked). zstd unchanged.

• Linux SFX stub supports both codecs. macOS SFX loader stays
  zstd-only for size (no_std + zstd-sys FFI, ~84 KB, < 1/5 of upxz); gzip on
  macOS goes through the cross-platform upxz run runner path.

• Refs: mneme story/feature/260626.upxz-tech/ §codec-agnostic; PR #9.

• upxz --bin <inner-path> <archive.tar.zst> [-- args...]: run a single
  designated binary directly out of a .tar.zst archive without extracting
  the whole archive (AppImage-style). Streams zstd → tar, materializes only
  the matched entry (Linux: memfd_create + fexecve, in-memory only; macOS:
  temp file + ad-hoc codesign), and execs it with argv forwarded verbatim and
  exit code propagated. Other entries are read and discarded, never written to
  disk.

• CLI fix: the SFX output is now -o/--out <packed> instead of a second
  positional. This fixes a latent bug where upxz foo.upxz -- -a -b (runner
  trailing args) was swallowed by the SFX-output positional slot. run and
  --bin trailing args now work reliably.

• New deps: tar = "0.4"; libc = "0.2" (Linux target only).

• Refs: PR #8.