fix(core): allow additional JSON Schema properties in elicitInput requestedSchema

Add .catchall(z.unknown()) to the requestedSchema object type in
ElicitRequestFormParamsSchema, matching the existing pattern used by
inputSchema and outputSchema. This fixes a type incompatibility when
passing Zod v4's .toJSONSchema() output (which includes $schema,
additionalProperties, etc.) to elicitInput's requestedSchema parameter.

Fixes #1362

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

Author: corvid-agent

.changeset/zod-json-schema-compat.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/core': patch
+---
+
+Allow additional JSON Schema properties in elicitInput's requestedSchema type by adding .catchall(z.unknown()), matching the pattern used by inputSchema. This fixes type incompatibility when using Zod v4's .toJSONSchema() output which includes extra properties like $schema and additionalProperties.

packages/core/src/types/types.ts

@@ -1993,11 +1993,13 @@ 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({
+            type: z.literal('object'),
+            properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
+            required: z.array(z.string()).optional()
+        })
+        .catchall(z.unknown())
 });
 
 /**