Agent-to-Agent Task Handoff#

Discovery and invocation cover "call a capability and get an answer." A2A covers something else: one agent hands a long job to a different agent, keeps working, and can cancel it mid-run — with the other side demonstrably stopping.

The distinction that decides whether you want this:

A2A is for parallelism, and the reason it exists as a separate surface is that the executing agent does not share your memory. Asking another agent to continue your work is briefing a colleague who wasn't in the room — so the protocol makes that explicit rather than pretending otherwise.

The brief carries references, not context#

A TaskBrief carries the job plus the context the executor needs as artifact references, not inlined content. That's deliberate: the other agent has its own memory, and inlining would imply a shared context that doesn't exist. Put the context in Dataforts and hand over the refs.

Lifecycle#

requested → accepted → running → completed{ref} | failed | cancelled

completed carries a reference to the result, for the same reason the brief carries references to the input.

Executor side#

let handles = mesh.serve_a2a(registry, executor)?;
// Hold the handles for as long as this agent should accept tasks —
// dropping them unregisters the services.

serve_a2a registers three services at once: accept a brief (spawning the executor), answer status, and cancel. Rollback is automatic — if registering the third fails, the first two unregister as the error returns, so you never end up half-serving.

A malformed brief does not fail out of band. It answers a TaskAck { accepted: false } that the requester reads, so a bad submission is a value on the happy path rather than an exception on a background task.

The node must be start()ed before serving.

Requester side#

let ack = mesh.submit_task(target, brief).await?;      // TaskAck
let rec = mesh.task_status(target, &task_id).await?;   // Option<TaskRecord>
let stopped = mesh.cancel_task(target, &task_id).await?;  // bool

task_status returns Option — None means the executor has no record of that id, which is different from "the task failed." cancel_task returns whether the cancel took effect, and the executor observes it through a CancelToken rather than being killed, so it can stop cleanly.

Bindings#

See also#

• Agent Identity — the delegation chain an enrolled agent carries
• Tool Federation — publishing tools other agents discover
• Blob Storage (Dataforts) — where brief and result refs point
• Submitted Is Not Completed