MetaCrate/docs/dependency-policy.md

Dependency and supply-chain policy

MetaCrate treats the locked dependency graph as reviewed release input. The canonical direct-dependency and duplicate-version inventory is ci/dependency-policy.json, and the native Rust metacrate-ci-matrix dependency-audit command compares that inventory with cargo metadata --locked --all-features.

The audit fails when a direct crate or resolved direct version is added or removed without review, duplicate versions drift, a registry dependency uses a wildcard, a package comes from Git or an unapproved registry, rationale is missing, or the dependency lacks an implemented responsibility in RUSTREWRITE.md. Its JSON evidence records every direct consumer and dependency scope, all approved duplicate sets, native direct dependencies, review dates, and the resolved external package count.

The policy intentionally distinguishes Rust 1.96.0, the minimum supported Rust version, from current stable Rust used for development and release validation. The release matrix checks both. Raising the MSRV requires an explicit policy, matrix, documentation, and changelog review; ordinary dependency updates may not raise it accidentally.

Automated gates

The Ubuntu-only consolidated required Gitea gate installs pinned versions of cargo-deny and cargo-machete, then runs:

cargo run --locked -p metacrate-ci-matrix -- \
  dependency-audit --evidence artifacts/dependency-audit.json
cargo deny check advisories licenses bans sources --hide-inclusion-graph
cargo machete --with-metadata

cargo-deny accepts only crates.io sources and the reviewed permissive license set in deny.toml. Advisory exceptions and license exceptions are empty. Duplicate versions are denied unless one exact version is listed with a reason; the Rust audit independently verifies the complete exact duplicate set across the lockfile, including target-specific packages. cargo-machete rejects unused direct dependencies. The only metadata exclusions are pkg-config and vcpkg in the two native adapter crates because their target-conditional use is directly visible in each build.rs.

Native and platform requirements

All native boundaries have Linux, Windows, and macOS strategies:

Boundary	Linux and macOS	Windows	Feature scope
libopus 1.3+	pkg-config package opus	vcpkg opus for MSVC; pkg-config for GNU	WebRTC voice crate
OpenJPEG 2.5.4+	pkg-config package libopenjp2	vcpkg openjpeg for MSVC; pkg-config for GNU	opt-in jpeg2000
j2k 0.8.1	pure Rust, no platform prerequisite	same pure-Rust graph	default rust-j2k
skia-rs-codec 0.3.0 and image-webp 0.2.4	pure Rust, no platform prerequisite	same pure-Rust graph	default rust-skia
Skia 0.99.0	target-specific official binary cache or source build	same target-specific strategy	opt-in skia
Vorbis 0.5.6 stack	vorbis_rs builds its reviewed C codec stack	same crate strategy	opt-in vorbis
Physical audio	ALSA development files on Linux; CoreAudio is system-provided on macOS	WASAPI is system-provided	opt-in real-audio

pkg-config and vcpkg only discover libraries; they are not runtime dependencies. libremetaverse-opus and libremetaverse-openjpeg are the only workspace crates allowed to contain unsafe ABI calls. They expose owned, validated safe Rust APIs and require exclusive mutable access to native codec state. No macOS-only API is used without Linux and Windows equivalents.

Review and update cadence

The graph is reviewed at least quarterly using reviewed_on and review_by. RustSec advisories are reviewed immediately. For every update:

1. identify the implemented caller and confirm the dependency remains needed;
2. inspect release notes, maintenance state, license, MSRV, enabled features, native code, and target-specific build behavior;
3. update one crate deliberately with cargo update -p NAME --precise VERSION;
4. rerun the dependency audit, cargo-deny, cargo-machete, and the affected release-matrix profiles from clean target directories;
5. update the exact policy versions and duplicate reasons only after reviewing the resulting transitive graph.

High-cost or native dependencies require isolated feature testing and all- features unification. A successful compile does not replace the real codec, secure WebRTC loopback, device, or live-grid gates applicable to that boundary. The abandoned audiopus/audiopus_sys stack is prohibited by absence from the direct inventory and by RustSec; MetaCrate instead binds the maintained system libopus ABI in its private adapter.