Crate a2a 

a2a

A2A (agent-to-agent) schema types for the substrate mailbox and tasklist.

This crate is schema-only: no engine adapters, no transport, no IO. Types map to the A2A protocol shape but are transport-agnostic.

Task lifecycle

Submitted -> Working -> InputRequired -> Working -> Completed with Failed and Cancelled reachable from any non-terminal state. Use TaskState::can_transition to validate moves.

Message lifecycle

Unread -> Delivered -> Consumed. Atomic claim semantics are enforced by the store layer (e.g. store-sqlite via UPDATE WHERE state='unread').

Re-exports

pub use error::A2aError;

pub use error::A2aResult;

pub use message::Artifact;

pub use message::Message;

pub use message::MessageKind;

pub use message::MsgState;

pub use message::Part;

pub use task::Task;

pub use task::TaskState;

Modules

error

Errors that may cross an a2a boundary.

message

Message, Part, MsgState, MessageKind, and Artifact types.

task

Task and TaskState types.