Drive resolver elicitation over the 2026-07-28 input_required flow

Resolvers that return Elicit[T] now negotiate the transport by protocol version:
at >= 2026-07-28 the framework returns an InputRequiredResult carrying the
batched questions and resumes when the client retries with
input_responses/request_state; at <= 2025-11-25 it keeps the synchronous
ctx.elicit() request. Author-facing code (Resolve/Elicit) is unchanged.

resolve_arguments becomes a resumable DAG walk: it reads ctx.input_responses /
ctx.request_state, memoizes resolver outcomes by a process-stable module:qualname
key, batches independent pending elicitations into one round, serializes
dependent ones across rounds, and carries resolved outcomes in request_state so
each resolver resolves once per logical call. Outcomes restored from
request_state are re-validated into their model via the Elicit[T] return arm.
request_state is client-trusted for now (HMAC sealing is a follow-up).

Add a render_elicitation_schema helper to elicitation.py, MRTR-loop and codec
tests, and document the transport in the migration guide.

Author: Kludex

src/mcp/server/elicitation.py

@@ -87,6 +87,18 @@ def _validate_rendered_properties(json_schema: dict[str, Any]) -> None:
             ) from None
 
 
+def render_elicitation_schema(schema: type[BaseModel]) -> dict[str, Any]:
+    """Render a model as the spec-valid `requested_schema` for an elicitation.
+
+    Raises:
+        TypeError: If a field renders as something the spec's
+            `PrimitiveSchemaDefinition` does not accept.
+    """
+    json_schema = schema.model_json_schema(schema_generator=_ElicitationJsonSchema)
+    _validate_rendered_properties(json_schema)
+    return json_schema
+
+
 async def elicit_with_validation(
     session: ServerSession,
     message: str,
@@ -103,8 +115,7 @@ async def elicit_with_validation(
 
     For sensitive data like credentials or OAuth flows, use elicit_url() instead.
     """
-    json_schema = schema.model_json_schema(schema_generator=_ElicitationJsonSchema)
-    _validate_rendered_properties(json_schema)
+    json_schema = render_elicitation_schema(schema)
 
     result = await session.elicit_form(
         message=message,