fix: don't treat callable standard schemas as function param matchers

.changeset/callable-param-matchers.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't treat callable standard schemas as function param matchers

packages/kit/src/exports/params.js

@@ -35,6 +35,15 @@ export function defineParams(definitions) {
  * @returns {import('@sveltejs/kit').ParamMatcher}
  */
 export function normalize_param_definition(definition) {
+	// standard schemas can be callable (e.g. ArkType), so this must be checked before the function case
+	if (
+		definition &&
+		(typeof definition === 'object' || typeof definition === 'function') &&
+		'~standard' in definition
+	) {
+		return definition;
+	}
+
 	if (typeof definition === 'function') {
 		return /** @type {import('@sveltejs/kit').ParamMatcher} */ (
 			/** @type {unknown} */ ({
@@ -55,9 +64,5 @@ export function normalize_param_definition(definition) {
 		);
 	}
 
-	if (definition && typeof definition === 'object' && '~standard' in definition) {
-		return definition;
-	}
-
 	throw new Error('Invalid param definition');
 }

packages/kit/src/utils/params.spec.js

@@ -72,3 +72,23 @@ test('normalize_param_definition propagates thrown errors', () => {
 
 	assert.throws(() => matcher['~standard'].validate('x'), /boom/);
 });
+
+test('normalize_param_definition passes callable standard schemas through untouched', () => {
+	// standard schemas can be callable (e.g. ArkType)
+	const callable = /** @type {import('@sveltejs/kit').ParamMatcher} */ (
+		/** @type {unknown} */ (
+			Object.assign(() => 'from-call', {
+				'~standard': {
+					version: 1,
+					vendor: 'test',
+					validate: () => ({ value: 'from-schema' })
+				}
+			})
+		)
+	);
+
+	const matcher = normalize_param_definition(callable);
+
+	assert.equal(matcher, callable);
+	assert.deepEqual(matcher['~standard'].validate('x'), { value: 'from-schema' });
+});