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

docs/migration.md

@@ -1528,6 +1528,8 @@ async def delete_folder(
 
 The `confirm_delete` resolver reads the tool's own `path` argument by name, lists the folder, and only elicits when the folder is non-empty - an empty folder resolves to `Confirm(ok=True)` with no round-trip to the client. Because `delete_folder` annotates the result union, it handles every outcome: the user accepting and confirming, accepting but declining to delete (`ok=False`), declining the elicitation, or cancelling it.
 
+The framework drives elicitation over whichever transport the negotiated protocol provides, so the resolver and tool code above is unchanged either way. At `2026-07-28` and later it returns an `InputRequiredResult` carrying the questions and resumes when the client retries `call_tool(..., input_responses=..., request_state=...)` (independent resolvers are batched into one round; a resolver that depends on another's answer is asked in a later round). At `2025-11-25` and earlier it issues a synchronous `elicitation/create` request mid-call. Elicited answers are carried in `request_state` across rounds, so each question is asked once; a resolver that resolves without eliciting is pure and may re-run each round.
+
 Resolved parameters are omitted from the tool's input schema, so the client never supplies them. Resolver parameters that cannot be classified, and cyclic resolver dependencies, raise at registration time.
 
 `ElicitationResult` is now a subscriptable generic alias (so `ElicitationResult[T]` works in annotations) instead of a plain union. A runtime `isinstance(result, ElicitationResult)` therefore raises `TypeError`; check against the member classes directly - `isinstance(result, AcceptedElicitation)` (or `DeclinedElicitation` / `CancelledElicitation`).

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,

src/mcp/server/mcpserver/context.py

@@ -238,6 +238,11 @@ def request_id(self) -> str:
         """Get the unique ID for this request."""
         return str(self.request_context.request_id)
 
+    @property
+    def protocol_version(self) -> str | None:
+        """The negotiated protocol version, or `None` outside of an active request."""
+        return self._request_context.protocol_version if self._request_context is not None else None
+
     @property
     def input_responses(self) -> InputResponses | None:
         """Client responses to a prior `InputRequiredResult.input_requests`.