diff --git a/src/validation/wire-schema.test.ts b/src/validation/wire-schema.test.ts
index 98fc4d7b..0c8a321b 100644
--- a/src/validation/wire-schema.test.ts
+++ b/src/validation/wire-schema.test.ts
@@ -117,6 +117,24 @@ describe('wireSchemaErrors', () => {
     ).toEqual([]);
   });
 
+  it('accepts extension result types through the generic result envelope', () => {
+    expect(
+      wireSchemaErrors(
+        DRAFT_PROTOCOL_VERSION,
+        {
+          jsonrpc: '2.0',
+          id: 3,
+          result: {
+            resultType: 'task',
+            taskId: 'task-1',
+            status: 'working'
+          }
+        },
+        'tools/call'
+      )
+    ).toEqual([]);
+  });
+
   it('accepts a JSON-RPC batch under 2025-03-26 and reports per-element errors', () => {
     expect(
       wireSchemaErrors('2025-03-26', [
diff --git a/src/validation/wire-schema.ts b/src/validation/wire-schema.ts
index 8b45849d..bf3dc5f9 100644
--- a/src/validation/wire-schema.ts
+++ b/src/validation/wire-schema.ts
@@ -261,15 +261,23 @@ export function wireSchemaErrors(
 
   if (msg.result !== undefined) {
     // SEP-2322 (MRTR): any request may be answered with an InputRequiredResult
-    // instead of its method's result type; discriminate on resultType.
+    // instead of its method's result type; discriminate on resultType. Results
+    // introduced by extensions use the same open discriminator and are checked
+    // against the generic result envelope until their schema is available here.
+    const resultType = (msg.result as Record<string, unknown> | null)
+      ?.resultType;
     const inputRequired =
-      (msg.result as Record<string, unknown> | null)?.resultType ===
-        'input_required' && 'InputRequiredResult' in spec.defs;
-    const resultDefName = inputRequired
-      ? 'InputRequiredResult'
-      : requestMethod !== undefined
-        ? spec.resultDefs.get(requestMethod)
-        : undefined;
+      resultType === 'input_required' && 'InputRequiredResult' in spec.defs;
+    const extensionResult =
+      typeof resultType === 'string' &&
+      resultType !== 'complete' &&
+      resultType !== 'input_required';
+    let resultDefName: string | undefined;
+    if (inputRequired) {
+      resultDefName = 'InputRequiredResult';
+    } else if (!extensionResult && requestMethod !== undefined) {
+      resultDefName = spec.resultDefs.get(requestMethod);
+    }
     if (resultDefName) {
       const typed = validateAgainst(resultDefName, msg.result).map(
         (e) => `${e} (result of '${requestMethod}')`