Context. Layer 1 — A2A Binding § Open Questions: "A2A's resumable-interrupt states could plausibly give Layer 6 (negotiation) a native 'task paused, awaiting counter-offer' mechanism. This is a Layer 6 question, not a Layer 1 one — noted here as a pointer, not resolved."
Today, Layer 6 negotiation happens entirely before acmp/invoke: offer, counter-offer, accept, then execution starts. Once a task is running there is no way to pause and renegotiate — a provider that discovers mid-task that the job is bigger than quoted can only finish at a loss, fail, or be cancelled.
What changed. Both of ACMP's candidate transport substrates now model exactly this pause:
- A2A has the
input-required / auth-required task states — non-terminal and resumable.
- MCP adds Multi Round-Trip Requests in its 2026-07-28 revision: a server returns
resultType: "input_required", and the client supplies what's missing by retrying the original request.
Two independent protocols converging on the same shape is a strong hint. It does not follow that ACMP should inherit it.
Your task. Work out whether Layer 6 should gain a paused-renegotiation mechanism, and what it would cost:
- What may trigger a pause — scope creep, a revised cost estimate, an ambiguity in the input? Or nothing, because that is what
max_price_cu and cancellation are already for?
- What travels in the interrupt: a fresh offer, a delta on the accepted one, or only a reason code?
- The hard part is economic, not syntactic. A paused task holds escrow while it waits (Layer 4). Who bears the cost of the wait, and what expiry turns a stalled pause into a partial settlement?
- What stops a provider from using mid-task renegotiation as a hostage tactic, having already consumed the buyer's deadline?
- Does this need Layer 1 wire support (
acmp/interrupt / acmp/resume, see Layer 1 § Open Questions), or can it ride on existing Layer 6 messages?
Done = a comment or PR taking a position on whether ACMP should adopt this at all, with the escrow-economics question at least sketched. A reasoned "no — here is why pre-invoke-only negotiation is the right constraint" is as valuable as a design.
Context. Layer 1 — A2A Binding § Open Questions: "A2A's resumable-interrupt states could plausibly give Layer 6 (negotiation) a native 'task paused, awaiting counter-offer' mechanism. This is a Layer 6 question, not a Layer 1 one — noted here as a pointer, not resolved."
Today, Layer 6 negotiation happens entirely before
acmp/invoke: offer, counter-offer, accept, then execution starts. Once a task is running there is no way to pause and renegotiate — a provider that discovers mid-task that the job is bigger than quoted can only finish at a loss, fail, or be cancelled.What changed. Both of ACMP's candidate transport substrates now model exactly this pause:
input-required/auth-requiredtask states — non-terminal and resumable.resultType: "input_required", and the client supplies what's missing by retrying the original request.Two independent protocols converging on the same shape is a strong hint. It does not follow that ACMP should inherit it.
Your task. Work out whether Layer 6 should gain a paused-renegotiation mechanism, and what it would cost:
max_price_cuand cancellation are already for?acmp/interrupt/acmp/resume, see Layer 1 § Open Questions), or can it ride on existing Layer 6 messages?Done = a comment or PR taking a position on whether ACMP should adopt this at all, with the escrow-economics question at least sketched. A reasoned "no — here is why pre-invoke-only negotiation is the right constraint" is as valuable as a design.