fix: widen requestedSchema type to accept additional JSON Schema fields

The `requestedSchema` object in `ElicitRequestFormParamsSchema` was too
narrow, rejecting valid JSON Schema fields like `additionalProperties`
that Zod v4's `.toJSONSchema()` and other JSON Schema generators produce.

Add `.passthrough()` to the `requestedSchema` Zod object and include
the `$schema` field (already present in the spec types) so that standard
JSON Schema output is accepted without type errors.

Fixes #1362

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Dave-London

packages/core/src/types/types.ts

@@ -1993,11 +1993,14 @@ export const ElicitRequestFormParamsSchema = TaskAugmentedRequestParamsSchema.ex
      * A restricted subset of JSON Schema.
      * Only top-level properties are allowed, without nesting.
      */
-    requestedSchema: z.object({
-        type: z.literal('object'),
-        properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
-        required: z.array(z.string()).optional()
-    })
+    requestedSchema: z
+        .object({
+            $schema: z.string().optional(),
+            type: z.literal('object'),
+            properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
+            required: z.array(z.string()).optional()
+        })
+        .passthrough()
 });
 
 /**

packages/core/test/spec.types.test.ts

@@ -53,6 +53,12 @@ type MakeUnknownsNotOptional<T> =
                       }
           : T;
 
+// Targeted fix: in spec, requestedSchema needs index signature to match SDK's .passthrough()
+// which allows additional JSON Schema fields like `additionalProperties` from Zod's .toJSONSchema()
+type FixSpecRequestedSchema<T> = T extends { requestedSchema: infer R }
+    ? Omit<T, 'requestedSchema'> & { requestedSchema: R & { [x: string]: unknown } }
+    : T;
+
 // Targeted fix: in spec, treat ClientCapabilities.elicitation?: object as Record<string, unknown>
 type FixSpecClientCapabilities<T> = T extends { elicitation?: object }
     ? Omit<T, 'elicitation'> & { elicitation?: Record<string, unknown> }
@@ -160,11 +166,14 @@ const sdkTypeChecks = {
         sdk = spec;
         spec = sdk;
     },
-    ElicitRequestParams: (sdk: SDKTypes.ElicitRequestParams, spec: SpecTypes.ElicitRequestParams) => {
+    ElicitRequestParams: (
+        sdk: SDKTypes.ElicitRequestParams,
+        spec: FixSpecRequestedSchema<SpecTypes.ElicitRequestFormParams> | SpecTypes.ElicitRequestURLParams
+    ) => {
         sdk = spec;
         spec = sdk;
     },
-    ElicitRequestFormParams: (sdk: SDKTypes.ElicitRequestFormParams, spec: SpecTypes.ElicitRequestFormParams) => {
+    ElicitRequestFormParams: (sdk: SDKTypes.ElicitRequestFormParams, spec: FixSpecRequestedSchema<SpecTypes.ElicitRequestFormParams>) => {
         sdk = spec;
         spec = sdk;
     },