PRODUCTION SCENARIO
Your deployment Model Context Protocol (MCP) server targets the 2026-07-28 specification, and the client it runs against declares support for both elicitation modes. Before the release tool can proceed it needs the human operator to pick a target region from four and confirm a rollout window. Neither value is a credential or a payment detail, and neither is anywhere in the conversation for the model to infer.
Which result should the tool return to collect them?
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Answer: An InputRequiredResult carrying a form-mode elicitation with a flat primitive schema
Elicitation is how a server asks the person for structured input mid-request: it returns an InputRequiredResult carrying an elicitation/create request, form-mode schemas are limited to flat objects with primitive properties, and the reply carries accept, decline or cancel, each of which the server handles. URL mode is required rather than optional for secrets and credentials, so a token or a payment step is what belongs there, and a region is neither. Sampling asks the client's model instead of the operator and is deprecated as of this revision. An execution error is the right shape when the model can supply what is missing, which it cannot do for a window only the operator knows.