fix: don't treat Object.prototype members as param matchers

.changeset/eleven-cases-guard.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: don't treat `Object.prototype` members as param matchers during validation

packages/kit/src/utils/params.js

@@ -25,7 +25,7 @@ export function collect_matcher_names(routes) {
  */
 export function validate_param_matchers(params, names, file) {
 	for (const name of names) {
-		if (!(name in params)) {
+		if (!Object.hasOwn(params, name)) {
 			throw new Error(`No matcher found for parameter '${name}'${file ? ` in ${file}` : ''}`);
 		}
 	}

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

@@ -23,6 +23,13 @@ test('validate_param_matchers throws for unknown matchers', () => {
 	);
 });
 
+test('validate_param_matchers ignores inherited properties', () => {
+	assert.throws(
+		() => validate_param_matchers({}, new Set(['toString']), 'params.js'),
+		/No matcher found for parameter 'toString'/
+	);
+});
+
 test('load_and_validate_params loads and validates params', async () => {
 	const params = await load_and_validate_params({
 		routes: [