v4.0.0: codec 2.60.4 security release, --pq-box sealed-box mode, F-16 fix

Major release. Highlights:

- Codec: vendored VaptVupt codec moves to canonical 2.60.4 security
  release. Fixes a high-severity OOB heap write in the AVX2 decode fast
  path (reachable on a valid stream sized to exactly content_size, both
  tail variants). Brings CBMC-formally-verified BCJ filters with
  automatic ELF/PE/Mach-O detection. Compressed output stays
  byte-identical (ratio gate Δ 0.00%); wire format unchanged at v1.6.
- New --pq-box sealed-box recipient mode (vendored libpqvaptvupt 0.6.0):
  ML-KEM-768 + X25519 combined via HKDF-SHA256 with domain separation,
  AES-256-CTR + HMAC-SHA256 EtM. Legacy --pq and --pq-sdk stay readable.
- F-16: discloses and fixes a pre-existing data-loss defect in the
  <= 3.8.0 in-tree BCJ encoder. Full back-compat matrix decodes
  byte-exact under 4.0.0; every readable pre-4.0 archive remains readable.

Repository hygiene:
- Sync full 4.0.0 source tree (codec, crypto, SDK, GUI, packaging, tests).
- Remove internal scratch files (PROMPT.md, FORMAL_AUDIT_PROMPT.md)
  and superseded version-specific docs (INTEGRATION_PROTOCOL_2.60.4.md,
  docs/FINDINGS-2.x.md) and a stray test binary.
- Refresh README download/install section to real 4.0.0 release assets;
  bump version badge to 4.0.0.
- Add .gitignore for build outputs (keeps vendored prebuilt libraries).

DISTRIBUTION.md

@@ -0,0 +1,268 @@
+# Distributing Zupt
+
+This document describes the upstream packaging recipes shipped under
+`packaging/` and the path from "local source tree" to "package
+installable on every major Linux distribution and macOS."
+
+Recipes are upstream-maintained but distro-submission-ready. Real
+submission to AUR / Debian / Fedora / Homebrew / NixOS is operational
+work outside this repository.
+
+## Producing a reproducible source tarball
+
+Every packaging recipe expects an upstream tarball `zupt-VERSION.tar.gz`
+produced by the project's `make dist` target. The tarball is
+**byte-reproducible**:
+
+```sh
+make dist
+# → /tmp/zupt-2.4.4.tar.gz
+# → sha256: 407d20ef03e5bf857195b99e04843ef3b07357416a4115add1e8aaa2007a769f
+# → bytes:  813113
+```
+
+Re-running `make dist` on the same source tree produces an identical
+sha256 (verified by `tests/test_dist_reproducible.sh`, wired into
+`make test`). This lets distros pin a stable hash in their recipes.
+
+The reproducibility properties:
+
+- Files sorted by name (deterministic order across filesystems)
+- mtime fixed to `SOURCE_DATE_EPOCH` (default `1747699200`; override
+  via env)
+- uid/gid pinned to root (0/0) via `--owner=0 --group=0 --numeric-owner`
+- gzip wrapped with `-9n` (no embedded timestamp or filename)
+- Source-only — no `.o`, no built binaries, no `.git/` tree
+- Includes the vendored `libzuptsdk.so.2.0.0` real file plus its two
+  symlinks (`libzuptsdk.so`, `libzuptsdk.so.2`)
+
+To force a specific epoch (for distro release-day pinning):
+
+```sh
+SOURCE_DATE_EPOCH=1727740800 make dist  # 2024-10-01 UTC
+```
+
+## Recipes shipped
+
+| Distro / Platform | Path                            | Format         |
+|-------------------|---------------------------------|----------------|
+| Arch Linux        | `packaging/aur/PKGBUILD`        | AUR PKGBUILD   |
+| Debian / Ubuntu   | `packaging/debian/`             | Source package (`3.0 (quilt)`) |
+| Fedora / RHEL     | `packaging/rpm/zupt.spec`       | RPM .spec      |
+| macOS             | `packaging/homebrew/zupt.rb`    | Homebrew formula |
+| NixOS / Nix flake | `packaging/nix/flake.nix`       | Nix flake      |
+
+All recipes:
+
+- Install the binary to `$PREFIX/bin/zupt` (default `/usr/bin/zupt`)
+- Install the vendored `libzuptsdk.so*` triple to `$PREFIX/lib/zupt/`
+  (the binary uses relative `rpath` so users don't need `LD_LIBRARY_PATH`)
+- Install manpage to `$PREFIX/share/man/man1/zupt.1.gz`
+- Install docs (README, SECURITY, CHANGELOG, AUDIT) to
+  `$PREFIX/share/doc/zupt/`
+- Run the full upstream regression suite (`make test`) during build
+  when the distro's package guidelines allow check-phase execution
+
+## Arch Linux (AUR)
+
+Maintainer flow:
+
+```sh
+# 1. Produce the upstream tarball
+make dist
+# → /tmp/zupt-2.4.4.tar.gz
+
+# 2. Upload to a stable URL (e.g. git.securityops.co releases)
+
+# 3. Update packaging/aur/PKGBUILD:
+#    - Set pkgver=2.4.4
+#    - Set sha256sums=("$(sha256sum /tmp/zupt-2.4.4.tar.gz | awk '{print $1}')")
+
+# 4. Generate .SRCINFO
+cd packaging/aur && makepkg --printsrcinfo > .SRCINFO
+
+# 5. Test locally
+makepkg -s
+
+# 6. Push to AUR
+git clone ssh://aur@aur.archlinux.org/zupt.git aur-zupt
+cp packaging/aur/PKGBUILD packaging/aur/.SRCINFO aur-zupt/
+cd aur-zupt && git add -A && git commit -m "v2.4.4" && git push
+```
+
+User install:
+
+```sh
+yay -S zupt          # or paru, pikaur, etc.
+```
+
+## Shell completions (v2.4.7+)
+
+`make install` automatically installs Bash, zsh, and fish completion
+files alongside the binary and manpage:
+
+| Shell | Path |
+|---|---|
+| Bash | `$PREFIX/share/bash-completion/completions/zupt` |
+| zsh  | `$PREFIX/share/zsh/site-functions/_zupt` |
+| fish | `$PREFIX/share/fish/vendor_completions.d/zupt.fish` |
+
+The source files live under `completions/` in the project tree.
+Distros that prefer a different install location should override
+the relevant paths in their `make install` invocation; the
+underlying recipe is straightforward.
+
+For per-user installation without root:
+
+```sh
+# Bash
+cp completions/zupt.bash ~/.local/share/bash-completion/completions/zupt
+
+# zsh (somewhere in $fpath; add the directory to ~/.zshrc if needed)
+cp completions/_zupt ~/.zsh/completion/_zupt
+
+# fish
+cp completions/zupt.fish ~/.config/fish/completions/zupt.fish
+```
+
+Completions cover every CLI flag the binary actually parses
+(`--kdf`, `--comment`, `--comment-file`, `--pq-sdk`, `--dedup`,
+etc.) and are validated on every CI run via
+`tests/test_completions_manpage.sh`.
+
+## Debian / Ubuntu
+
+The `packaging/debian/` tree is a Debian source-package layout.
+Maintainer flow:
+
+```sh
+# 1. Produce the upstream tarball with the standard Debian
+#    orig.tar.gz naming convention:
+make dist
+cp /tmp/zupt-2.4.4.tar.gz /tmp/zupt_2.4.4.orig.tar.gz
+
+# 2. Unpack and overlay the debian/ tree:
+cd /tmp && tar xzf zupt_2.4.4.orig.tar.gz && cd zupt-2.4.4
+cp -a /path/to/zupt/packaging/debian ./debian
+
+# 3. Build the source package:
+dpkg-buildpackage -S -us -uc       # source-only
+dpkg-buildpackage -b -us -uc       # binary
+
+# 4. Lint:
+lintian zupt_2.4.4-1_*.deb
+
+# 5. Submit via the standard Debian mentors process:
+#    https://mentors.debian.net/intro-maintainers/
+```
+
+User install (after the package lands in Debian unstable / Ubuntu):
+
+```sh
+sudo apt install zupt
+```
+
+## Fedora / RHEL / CentOS
+
+```sh
+# 1. Produce the tarball
+make dist
+cp /tmp/zupt-2.4.4.tar.gz ~/rpmbuild/SOURCES/
+
+# 2. Drop the .spec into the SPECS directory:
+cp packaging/rpm/zupt.spec ~/rpmbuild/SPECS/
+
+# 3. Build source + binary RPMs:
+cd ~/rpmbuild && rpmbuild -ba SPECS/zupt.spec
+
+# 4. Lint:
+rpmlint RPMS/x86_64/zupt-2.4.4-1.fc*.rpm
+
+# 5. Submit via the Fedora new-package review process:
+#    https://docs.fedoraproject.org/en-US/package-maintainers/Package_Review_Process/
+#    EPEL automatically inherits Fedora packages.
+```
+
+User install (after the package lands in Fedora / EPEL):
+
+```sh
+sudo dnf install zupt                 # Fedora
+sudo dnf install epel-release zupt    # RHEL/CentOS via EPEL
+```
+
+## macOS (Homebrew)
+
+```sh
+# 1. Produce the tarball and upload to a stable release URL.
+
+# 2. Update packaging/homebrew/zupt.rb:
+#    - Set url to the release URL
+#    - Set sha256 to the upstream tarball sha256
+
+# 3. Test locally:
+brew install --build-from-source ./packaging/homebrew/zupt.rb
+brew test zupt
+brew audit --strict --online zupt
+
+# 4. Submit to homebrew-core (preferred, requires popularity threshold):
+#    https://docs.brew.sh/Adding-Software-to-Homebrew
+#
+#    OR host in your own tap:
+#    https://docs.brew.sh/How-to-Create-and-Maintain-a-Tap
+```
+
+User install (after submission lands):
+
+```sh
+brew install zupt
+# OR from a custom tap:
+brew install cristiancmoises/tap/zupt
+```
+
+## NixOS / Nix flake
+
+```sh
+# 1. Build directly from the flake (no central submission needed):
+nix build github:cristiancmoises/zupt#zupt
+nix run github:cristiancmoises/zupt#zupt -- version
+
+# 2. To consume from another flake:
+#    inputs.zupt.url = "github:cristiancmoises/zupt?ref=v2.4.4";
+#    packages.x86_64-linux.default = inputs.zupt.packages.x86_64-linux.zupt;
+
+# 3. To submit to nixpkgs (https://github.com/NixOS/nixpkgs):
+#    - Adapt packaging/nix/flake.nix's `zupt` derivation into a
+#      pkgs/by-name/zu/zupt/package.nix using fetchurl and a hash.
+#    - Follow the nixpkgs contribution guide:
+#      https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md
+```
+
+## Submitting upstream — checklist
+
+Before pushing any recipe to a distro repository:
+
+- [ ] `make dist` produces a reproducible tarball (verified by
+      `tests/test_dist_reproducible.sh` on every `make test`)
+- [ ] The tarball is uploaded to a stable, immutable URL
+- [ ] The recipe's checksum field is updated to match
+      `sha256sum /tmp/zupt-VERSION.tar.gz`
+- [ ] The recipe builds and tests pass in a clean chroot/container
+- [ ] The CHANGELOG mentions distro-relevant changes since the last release
+- [ ] The license metadata is correct (AGPL-3.0-or-later for Zupt core;
+      GPL-3.0-or-later for the vendored VaptVupt codec)
+
+## Security posture for downstream
+
+Every packaging recipe runs `make test` during build (`check()` for AUR,
+`override_dh_auto_test` for Debian, `%check` for RPM, `checkPhase` for
+Nix, `test` block for Homebrew). The suite includes:
+
+- **F-06**: 2 000 HMAC tamper trials, 0 silent accepts required
+- **F-08**: top-MAC header/footer integrity-trailer regression
+- **F-09**: 1 827-position exhaustive byte sweep on PQ-SDK archive,
+  0 silent accepts required
+- **F-10..F-12**: KDF default, auth-fail message, encrypted comments
+- **dist reproducibility**: `make dist` byte-identical across two runs
+
+A build that doesn't pass `make test` will fail at distro check time —
+the recipes don't paper over regressions.