A2A Mesh Extension

The AGBoss mesh extension — https://agboss.dev/a2a/mesh/v1

A profile extension of A2A v1.0 (spec §4.6): what an AGBoss application adds to a call between two AGBoss applications — the caller's call chain (loop and hop limits), its budget and deadline left, and the receiver's signed run report of what the call spent. An agent that does not support it is called without it, and the caller says so (mesh: false); nothing of it is ever assumed. A breaking change takes a new URI. (#809 the client, #810 the server; to be mirrored at agboss.dev.)

Declaration — the Agent Card

{
  "uri": "https://agboss.dev/a2a/mesh/v1",
  "required": false,
  "params": { "idempotencyRetention": "PT86400S" }
}

• params.idempotencyRetention (ISO 8601 duration of seconds): how long the agent deduplicates a messageId per caller — the same message resent within it gets the same task. Its presence makes the agent an AGBoss peer to a client: an ambiguous send may be resent with the same messageId within it, never to any other agent.

Activation

The client sends A2A-Extensions: https://agboss.dev/a2a/mesh/v1 (and a W3C traceparent) with a SendMessage; the agent echoes the URI in its answer's A2A-Extensions when it activated it. A client treats a call whose answer does not echo it as one without the mesh.

The envelope — message.metadata[uri].envelope

A compact JWS of type agboss-mesh: signed EdDSA with the caller's Ed25519 key, or unsecured (alg: "none", a claim only). Its payload, schema 1:

Field
issuer	the calling application
audience	the receiving application — required when signed
origin	the calling execution: rootExecutionId, executionId, workflow, step.idempotencyKey
callChain	[{ application, start, executionId }], the first caller first, the caller last
issuedAt, expiresIn	the replay window (PT60S)
bodyHash	sha256:<hex> of the RFC 8785 canonical JSON of the Message as sent, with metadata[uri] removed (and metadata when it is then empty)
budget	{ remaining: "<USD decimal>", currency: "USD" } — what the caller may still spend
deadline	{ remaining: "<ISO 8601 duration>" } — how long the caller still waits

The receiver's checks, in order, before anything runs

1. The audience: addressed to another application → 401 { "code": "mesh.audience-mismatch" }; signed and addressed to none → 401 mesh.audience-missing — before any signature is looked at.
2. A known issuer's signature (mesh.signature-invalid), replay window (mesh.envelope-expired) and body (mesh.body-mismatch), each 401.
3. The chain, on every envelope: the receiver's own (application, skill) already in it, or the chain as long as its maxMeshHops → a REJECTED task, nothing run, with status.message.metadata[uri] = { "code": "limit.mesh-loop" | "limit.hops", "details": { "entry", "chain", "maxMeshHops"? } }.
4. Trusted — the authenticated caller is the envelope's verified issuer — its budget and deadline bind the execution, its origin is the execution's.

A failed task's stable code is in status.message.metadata[uri].code; only the two mesh limits carry details, no other error's facts leave the application.

The run report — task.metadata[uri].report

On a completed task of a trusted caller (and on its stream's last status update): a compact JWS of type agboss-mesh-report, signed by the receiver, payload { schema: 1, issuer, executionId (the task's id), spend: { total, currency: "USD" }, bodyHash (the first message's), issuedAt }. The caller verifies it with the issuer's key, its own bodyHash and its task's id, and charges max(verified spend, contract price) — once, whichever of its passes reads it.

See A2A → §6.1 for the framework's side.