Architecture

Agate is a Cargo workspace in which each crate is one bounded context. Inside a context, Clean Architecture layers are modules and files are grouped by DDD object type. Dependencies flow inward only, and there is no shared kernel — cross-context technical capabilities (such as cryptography) are published as generic-subdomain libraries, not shared domain models.

The crate graph

flowchart TD
    server["agate-server<br/>composition root"]
    proxy["agate-proxy<br/>data plane"]
    policy["agate-policy<br/>content/authz decisions"]
    audit["agate-audit<br/>transparency log"]
    crypto["agate-crypto<br/>crypto agility (library)"]

    server --> proxy
    server --> audit
    server --> policy
    audit --> crypto

    classDef root fill:#0b7285,stroke:#0b7285,color:#fff;
    class server root;

agate-server composes the others behind their public ports. agate-proxy and agate-policy never depend on each other directly — their vocabularies meet only at the composition root, which translates between them. agate-audit depends on agate-crypto for hashing and signing strategies.

The single decision seam

The whole system pivots on one seam in the proxy: for each inspected event (or each buffered logical unit such as a complete tool call), a verdict is produced.

flowchart LR
    ev["Inspected event"] --> seam{{"event → verdict"}}
    seam --> allow["Allow — forward unchanged"]
    seam --> deny["Deny — block (RUN_ERROR)"]
    seam --> transform["Transform — forward modified"]
    seam --> buffer["Buffer — need more frames"]
    seam --> terminate["Terminate — end the run"]
    seam -.->|asks| policy["agate-policy"]
    seam -.->|"records (event, verdict)"| audit["agate-audit"]

Read on

• Architecture & DDD — the dependency rule, the no-shared-kernel decision, and the DDD building blocks (value objects, entities, aggregates, factories, ports) as applied in Rust.
• Threat Model — what the proxy defends, against whom, and the deployment topology.
• Bounded Contexts — one page per crate: crypto · audit · proxy · policy · server.