handle edge case

packages/adapter-vercel/index.js

@@ -444,9 +444,17 @@ function static_vercel_config(builder, config, dir) {
 	/** @type {import('./index.js').ImagesConfig | undefined} */
 	const images = config.images;
 
-	for (const [src, redirect] of builder.prerendered.redirects) {
+	for (let [src, redirect] of builder.prerendered.redirects) {
+		if (src.replace(/\/$/, '') !== redirect.location.replace(/\/$/, '')) {
+			// handle the extreme edge case of a `/foo` -> `/foo/` redirect,
+			// which would only arise if the response was generated by a
+			// `handle` hook or outside the app altogether (since you
+			// can't declaratively create both routes)
+			src = src.replace(/\/?$/, '/?');
+		}
+
 		prerendered_redirects.push({
-			src: src.replace(/\/?$/, '/?'),
+			src,
 			headers: {
 				Location: redirect.location
 			},