Distribution policy: builds, formats and what reads what

Status: measured on 2026-09-24 with the two build configurations of the reference implementation (tsaur/), the benchmark corpora and the tsaur CLI; the golden-archive matrix of §5 is produced by tools/compat_check.py from the release binaries. Percentages are archive size relative to the input (lower is better).

1. The two builds

Build	Cargo command	Contains	Creates	Reads
full (default)	cargo build --release	everything, including Lepton JPEG recompression (lepton_jpeg); like every build it contains cabac (LGPL-3.0-or-later) through preflate-rs	every archive kind	every valid archive
lite	cargo build --release --no-default-features	everything except Lepton; still contains cabac (LGPL-3.0-or-later) through preflate-rs	every archive kind except Lepton segments: JPEG files and DCTDecode streams are stored as they are (still bit-exact, just not smaller)	every archive without Lepton segments

Both builds produce byte-identical archives for inputs without JPEG content (checked: the 10-file benchmark corpus packs to the same 956,731 bytes with either binary). Volume sets (.tsrv) treat the archive as opaque bytes: either build splits, inspects, joins and repairs the volumes of any archive, including one that only the full build can open afterwards.

2. Compatibility matrix (measured)

Archive corpus_real (13 real DOCX/PDF/JPEG files, 578,890 bytes):

Archive created by	Size	Reader	list	info	verify	unpack
full (Lepton segments for 3 JPEGs)	453,116 B (78.3 %)	full	ok	ok	ok	ok, bit-exact
full (Lepton segments)	453,116 B	lite	ok	ok, reports requires: lepton	fails (exit 2, JPEG entries reported bad)	fails (exit 7: “this build has no Lepton support”)
lite (JPEGs stored raw, 3 container fallbacks)	505,943 B (87.4 %)	full	ok	ok	ok	ok, bit-exact
lite	lite	ok	ok	ok	ok, bit-exact
any build, archive without JPEG content (corpus, 956,731 B)	identical bytes	full or lite	ok	ok	ok	ok, bit-exact
any Lepton archive split into volumes by the full build	–	lite volumes join	–	–	–	joined file byte-identical (opening it still needs the full build)

Every archive records what it needs: tsaur list --json, tsaur info and tsaur verify --json report requires (today only lepton) and, when the running build lacks it, missing_features, so a user knows before extracting which binary to use. Entries that are not JPEG-based are readable by the lite build even inside an archive that contains Lepton segments (grep, read, stat on those entries work; unpack of the whole archive does not).

What disabling the feature does not do: it does not make every existing archive portable. An archive that contains Lepton segments needs a Lepton-capable reader for those entries, whichever binary created it. Archives that must be readable by the lite build must be created with the lite build or with pack --no-container.

3. Public distribution: the v1.0 decision

1. Source is the primary distribution: Apache-2.0 OR MIT, complete, with Cargo.lock pinning every dependency version. Anyone can build either configuration.
2. The recommended public binary is the lite build, packaged as tsaur-<version>-<platform>-lite.zip. Every archive it writes opens in every build. It contains, like every build, the LGPL-3.0 component cabac through preflate-rs (see §3.4 and THIRD-PARTY-NOTICES.md); a redistributor (someone bundling tsaur into a product or an image) takes on the obligations of §3.4 with either build, and the permissive notices for everything else. Its cost is measurable and documented: JPEG files and PDF images are stored as they are (corpus_real: 87.4 % instead of 78.3 %; everything else is identical).
3. The full build is built from source (cargo build --release) by users who want Lepton JPEG recompression and accept that archives containing recompressed JPEGs need the full build to open (pack --no-lepton in the full build writes universal archives). The release workflow publishes lite packages only; tools/package.py also builds a -full.zip for the release gate’s clean- directory check, and either package carries THIRD-PARTY-NOTICES.md, licenses/LGPL-3.0.txt and licenses/GPL-3.0.txt.
4. LGPL obligations of every binary (both builds contain cabac through preflate-rs; until 2026-09-25 this section wrongly spoke of the full binary only), as the project reads LGPL-3.0 §4 for a statically linked library: prominent notice (THIRD-PARTY-NOTICES.md), the license texts, and the Corresponding Application Code in a form that permits relinking, which the complete Apache/MIT source with Cargo.lock provides (cargo vendor reproduces the exact cabac sources). This reading has not been confirmed by counsel, and the maintainer decided on 2026-09-25 not to seek that confirmation. It remains the material uncertainty of this policy: no test can settle it, which is why every package carries the notices, the license texts and a pointer to the complete sources. A distributor of either binary who wants certainty should obtain their own legal advice; the project does not claim that the question is closed, and removing cabac from every build is roadmap item 1.1 so that the question disappears.
5. Packages are built and checked by tools/package.py: each zip is unpacked in a clean directory and the packaged binary runs every command of docs/GUIDE.md; sizes and SHA-256 values are written to dist/SHA256SUMS and dist/PACKAGES.md. Nothing is uploaded by the tool.
6. No superiority or security claims in release material beyond what benchmarks/RESULTS-rust.md and the test suite show, with the corpus, the command lines and “lower is better” stated next to every percentage.
7. Format stays the same in both builds: docs/spec/TSAUR-FORMAT-SPEC-v1.0.md registers Lepton as segment kind 2 of a stream recipe; a second implementation may use any Lepton decoder.

4. Reproducing the matrix

cd tsaur
cargo build --release                                            # full
cargo build --release --no-default-features --target-dir target-nolepton   # lite
./target/release/tsaur pack full.tsr ../benchmarks/corpus_real
./target-nolepton/release/tsaur pack lite.tsr ../benchmarks/corpus_real
./target-nolepton/release/tsaur info full.tsr --json | grep -A2 requires
./target-nolepton/release/tsaur unpack full.tsr out/    # exit 7: needs the full build
./target/release/tsaur unpack lite.tsr out/             # ok