Cargo

AXM reads Rust extension metadata from package.metadata.agentExtensions in Cargo.toml. This is the two-way linking model applied to the Cargo ecosystem.

Add an agentExtensions array under [package.metadata] in Cargo.toml. Each entry is an extension reference (@owner/<type>/<name>):

# Cargo.toml
[package]
name = "agentxm-example-tinyflags"
version = "0.1.0"

[package.metadata]
agentExtensions = [{ ref = "@examples/packs/rust-cargo-tinyflags" }]

Cargo ignores keys under package.metadata, so this table travels with your published crate without affecting the build.

Keep recommendations identity-only — omit versionRange. AXM resolves the reference to the newest matching extension version and pins it in the user's axm.lock. Prefer recommending a single pack so you keep one stable reference while its contents evolve.

Add a semver versionRange only when your crate genuinely pairs with a bounded major line of the extension:

[package.metadata]
agentExtensions = [
  { ref = "@examples/packs/rust-cargo-tinyflags", versionRange = "^1.0.0" },
]

On the extension manifest (skill.json, pack.json, subagent.json, …), add a packages array with a Cargo purl:

// pack.json
{
  "packages": [{ "purl": "pkg:cargo/agentxm-example-tinyflags" }],
}

Use the crate's name from crates.io as the purl name.

Default to identity-only. Add a VERS versionRange with the cargo scheme only when the extension depends on crate APIs introduced or removed in a known range:

{
  "packages": [
    {
      "purl": "pkg:cargo/agentxm-example-tinyflags",
      "versionRange": "vers:cargo/>=0.1.0|<1.0.0",
    },
  ],
}

When the Cargo crate recommends an extension through the AgentXM Registry and that extension names the crate as a companion via its purl, AXM derives official status for the pair — no extra flag. See Official extensions.

The rust-cargo-lib and rust-cargo-app directories in polyglot-examples are the working fixtures for everything above. The crate publishes a TinyFlags companion pack and recommends it from package.metadata.agentExtensions in Cargo.toml; the pack and each skill declare the crate's Cargo purl as an identity-only companion package.