Let the agent sleep until there is something worth reasoning about.

Long-running APIs, A2A tasks, and webhooks can tempt an orchestration loop to wake an expensive reasoning agent repeatedly. A Callback Mailbox receives the result while that agent is suspended.

Illustrative economics

This is an example, not a savings claim. Plain HTTP polling does not consume model tokens unless your orchestration routes those checks through a model. Use your measured marginal cost—including model, compute, API, and orchestration costs—and buy only when the result is positive.

What the mailbox adds

It provisions a temporary authenticated callback endpoint, stores ordered results, supports cursor retrieval, and applies replay-safe purchase handling. The agent keeps its wallet keys; Foundry accepts only the payment proof.