fix(types): annotate JSON*Schema with input type so isSpecType narrows

JSONValueSchema/JSONObjectSchema/JSONArraySchema were typed as
z.ZodType<T> (output only). Zod v4's ZodType<O, I> defaults I to
unknown, so z.input<typeof JSONValueSchema> was unknown and
isSpecType.JSONValue was (v: unknown) => v is unknown, a no-op
predicate. Annotating as z.ZodType<T, T> fixes the input type at the
source (these schemas have no defaults/transforms, so input equals
output). Test asserts the narrowing.

Author: felixweinberger

packages/core/src/types/schemas.ts

@@ -12,11 +12,11 @@ import type {
     ResultTypeMap
 } from './types.js';
 
-export const JSONValueSchema: z.ZodType<JSONValue> = z.lazy(() =>
+export const JSONValueSchema: z.ZodType<JSONValue, JSONValue> = z.lazy(() =>
     z.union([z.string(), z.number(), z.boolean(), z.null(), z.record(z.string(), JSONValueSchema), z.array(JSONValueSchema)])
 );
-export const JSONObjectSchema: z.ZodType<JSONObject> = z.record(z.string(), JSONValueSchema);
-export const JSONArraySchema: z.ZodType<JSONArray> = z.array(JSONValueSchema);
+export const JSONObjectSchema: z.ZodType<JSONObject, JSONObject> = z.record(z.string(), JSONValueSchema);
+export const JSONArraySchema: z.ZodType<JSONArray, JSONArray> = z.array(JSONValueSchema);
 /**
  * A progress token, used to associate progress notifications with the original request.
  */

packages/core/test/types/specTypeSchema.test.ts

@@ -3,7 +3,16 @@ import { describe, expect, expectTypeOf, it } from 'vitest';
 import type { OAuthMetadata, OAuthTokens } from '../../src/shared/auth.js';
 import type { SpecTypeName, SpecTypes } from '../../src/types/specTypeSchema.js';
 import { isSpecType, specTypeSchemas } from '../../src/types/specTypeSchema.js';
-import type { CallToolResult, ContentBlock, Implementation, JSONRPCRequest, ResourceTemplateType, Tool } from '../../src/types/types.js';
+import type {
+    CallToolResult,
+    ContentBlock,
+    Implementation,
+    JSONObject,
+    JSONRPCRequest,
+    JSONValue,
+    ResourceTemplateType,
+    Tool
+} from '../../src/types/types.js';
 
 describe('specTypeSchemas', () => {
     it('returns a StandardSchemaV1 validator that accepts valid values', () => {
@@ -91,6 +100,18 @@ describe('isSpecType', () => {
         }
     });
 
+    it('JSONValue / JSONObject — narrows to the JSON type, not unknown', () => {
+        // These schemas use an explicit z.ZodType<T, T> annotation for recursion; without the
+        // second param Zod's Input defaults to `unknown` and the predicate would not narrow.
+        const v: unknown = { a: 1 };
+        if (isSpecType.JSONValue(v)) {
+            expectTypeOf(v).toEqualTypeOf<JSONValue>();
+        }
+        if (isSpecType.JSONObject(v)) {
+            expectTypeOf(v).toEqualTypeOf<JSONObject>();
+        }
+    });
+
     it('guards work as filter callbacks and narrow the element type', () => {
         const mixed: unknown[] = [{ type: 'text', text: 'hi' }, 42, { type: 'text' }];
         const blocks = mixed.filter(isSpecType.ContentBlock);