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  and superseded version-specific docs (INTEGRATION_PROTOCOL_2.60.4.md,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).

packaging/homebrew/vaptvupt.rb

@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+# Homebrew formula for zupt.
+#
+# To publish:
+#   1. Run `make dist` upstream to produce zupt-VERSION.tar.gz (reproducible).
+#   2. Upload to a stable release URL.
+#   3. Update `url`, `version`, and `sha256` below.
+#   4. Submit to homebrew-core via PR OR host in your own tap
+#      (e.g. cristiancmoises/homebrew-tap).
+#
+# Local test:
+#   brew install --build-from-source ./zupt.rb
+#   brew test zupt
+#   brew audit --strict --online zupt
+#
+# Notes for macOS:
+#   * Jasmin assembly is disabled at build time on Darwin (no jasminc dep);
+#     the C fallback for AES-256-CTR / HMAC compare paths is shipped.
+#   * libzuptsdk is vendored and installed alongside the binary; the binary
+#     uses @loader_path rpath so users don't have to set DYLD paths.
+
+class Vaptvupt < Formula
+  desc "Post-quantum backup compression utility (ML-KEM-768 + AES-256-CTR + HMAC-SHA256)"
+  homepage "https://git.securityops.co/cristiancmoises/zupt"
+  url "https://git.securityops.co/cristiancmoises/zupt/releases/download/v4.0.0/vaptvupt-4.0.0.tar.gz"
+  version "4.0.0"
+  sha256 "REPLACE_WITH_SHA256_OF_RELEASE_TARBALL"
+  license "AGPL-3.0-or-later"
+
+  depends_on "python@3.12" => :test  # only for test-suite tamper harness
+
+  def install
+    # macOS build: no Jasmin, C-fallback crypto paths are used.
+    # The Makefile auto-detects Jasmin availability and falls back cleanly.
+    ENV["CFLAGS"] = "#{ENV.cflags} -O2 -std=c11 -Wall -Wextra"
+
+    system "make", "-j#{ENV.make_jobs}"
+    system "make", "DESTDIR=#{prefix}", "PREFIX=", "install"
+
+    # Vendored libzuptsdk goes into lib/zupt/ with @loader_path rpath.
+    # Note: Linux ships .so.2.0.0; macOS .dylib equivalent must be built
+    # separately by the vendored makefile. For the initial Homebrew
+    # submission this assumes the upstream tarball includes a .dylib build;
+    # if not, build it here.
+    lib_zupt = lib/"zupt"
+    lib_zupt.mkpath
+    if File.exist?("vendor/zuptsdk/libzuptsdk.dylib")
+      cp "vendor/zuptsdk/libzuptsdk.dylib", lib_zupt
+    elsif File.exist?("vendor/zuptsdk/libzuptsdk.so.2.0.0")
+      # Fallback: link Linux-style .so on macOS (works for direct loads but
+      # not for dlopen-on-Darwin scenarios). Upstream is tracking this.
+      cp "vendor/zuptsdk/libzuptsdk.so.2.0.0", lib_zupt
+    end
+
+    # Docs
+    doc.install "README.md", "SECURITY.md", "CHANGELOG.md", "AUDIT.md"
+  end
+
+  test do
+    # End-to-end sanity check: build a real archive, extract it, byte-compare.
+    (testpath/"input.txt").write("homebrew formula test payload\n")
+    system bin/"zupt", "c", "-p", "test", "out.zupt", "input.txt"
+    system bin/"zupt", "info", "out.zupt"
+    mkdir "extracted"
+    cd "extracted" do
+      system bin/"zupt", "x", "-p", "test", "../out.zupt"
+    end
+    system "diff", "-q", "input.txt", "extracted/input.txt"
+  end
+end