protocol

mcp_multiround_protocol

Protocol for multi-round tool/prompt/resource operations (MRTR) used by the MCP 2026-07-28 specification. Implementing objects may define the round hooks to request additional input from the client (elicitation, sampling, roots) and to resume with input responses and opaque request state. Existing applications that do not implement these hooks continue to use tool_call/3, prompt_get/3, resource_read/3, or auto-dispatch; the 2026 adapter wraps those results as complete(Result). The 2026 adapter never invokes the 2025-06-18 tool_call/4 elicitation API.

Availability:
logtalk_load(mcp_server(loader))
Author: Paulo Moura
Version: 1:0:0
Date: 2026-08-14
Compilation flags:
static
Dependencies:
(none)
Remarks:

  • Request context: Each round hook receives a request_context(ClientCapabilities, InputResponses, RequestState, Progress) term. ClientCapabilities is the curly-term advertised by the client. InputResponses is a list of input_response(Key, Response) terms (or empty on the first round). RequestState is application-owned opaque data (or none). Progress is a callable closure for emitting progress notifications when the client supplied a progress token; it is only meaningful under the 2026 adapter.

  • Complete results: A hook returns complete(Result) where Result uses the existing canonical vocabulary: text(Atom), error(Atom), results(List), structured(StructuredContent), structured(Items, StructuredContent) for tools; messages(MessageList) or messages(Description, MessageList) for prompts; contents(ContentList) for resources.

  • Input-required results: A hook returns input_required(InputRequests, RequestState). InputRequests is a nonempty list of uniquely keyed input_request(Key, Request) terms, and/or RequestState is non-none. An input-required result must contain a nonempty request list, non-none state, or both.

  • Allowed request forms: Request may be form_elicitation(Message, Schema), url_elicitation(Message, URL), sampling(Messages, ModelPreferences, SystemPrompt, IncludeContext), or roots.

  • Input responses: On a subsequent round the adapter supplies InputResponses with the same keys. Response values are accept(Content), decline, cancel (elicitation), sampling results, or roots results. Unrecognized keys are ignored. Malformed known values yield a -32602 error. Missing required responses cause the adapter to re-issue the corresponding input requests.

  • State integrity: RequestState is opaque to the adapter. Applications that use it for authorization or business decisions must integrity-protect, bind, and validate it themselves.

Inherited public predicates:
(none)

Public predicates

tool_call_round/4

Handles one round of a multi-round tool call. Name is the MCP tool name, Arguments is a list of ArgumentName-Value pairs, Context is a request_context(ClientCapabilities, InputResponses, RequestState, Progress) term, and RoundResult is unified with either complete(Result) or input_required(InputRequests, RequestState). If not defined, the 2026 adapter falls back to tool_call/3 (or auto-dispatch) and wraps the outcome as complete.

Compilation flags:
static
Template:
tool_call_round(Name,Arguments,Context,RoundResult)
Mode and number of proofs:
tool_call_round(+atom,+list(pair),+compound,--compound) - zero_or_one

prompt_get_round/4

Handles one round of a multi-round prompt get. Name is the MCP prompt name, Arguments is a list of ArgumentName-Value pairs, Context is a request_context/4 term, and RoundResult is unified with either complete(Result) or input_required(InputRequests, RequestState). If not defined, the 2026 adapter falls back to prompt_get/3 and wraps the outcome as complete.

Compilation flags:
static
Template:
prompt_get_round(Name,Arguments,Context,RoundResult)
Mode and number of proofs:
prompt_get_round(+atom,+list(pair),+compound,--compound) - zero_or_one

resource_read_round/4

Handles one round of a multi-round resource read. URI is the resource identifier, Arguments is a list of ArgumentName-Value pairs (currently unused by most applications), Context is a request_context/4 term, and RoundResult is unified with either complete(Result) or input_required(InputRequests, RequestState). If not defined, the 2026 adapter falls back to resource_read/3 and wraps the outcome as complete.

Compilation flags:
static
Template:
resource_read_round(URI,Arguments,Context,RoundResult)
Mode and number of proofs:
resource_read_round(+atom,+list(pair),+compound,--compound) - zero_or_one

Protected predicates

(none)

Private predicates

(none)

Operators

(none)