fix: skip hooks for server fetch to prerendered routes

Doing a server-side `fetch()` (e.g. `isSubRequest: true`) to a route
that is prerendered runs `hooks.server.js`,
which is different behaviour from a normal `fetch()`.

.changeset/nine-llamas-fetch.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: skip hooks for server fetch to prerendered routes

packages/kit/src/runtime/server/fetch.js

@@ -112,6 +112,14 @@ export function create_fetch({ event, options, manifest, state, get_cookie_heade
 					return await fetch(request);
 				}
 
+				if (manifest._.prerendered_routes.has(decoded)) {
+					// the prerendered logic is different for each adapter,
+					// (except maybe for prerendered redirects)
+					// so we need to make an actual HTTP request
+					// We do it here to avoid calling server-side hooks for prerendered routes
+					return await fetch(request);
+				}
+
 				if (credentials !== 'omit') {
 					const cookie = get_cookie_header(url, request.headers.get('cookie'));
 					if (cookie) {

packages/kit/src/runtime/server/respond.js

@@ -141,7 +141,7 @@ export async function respond(request, options, manifest, state) {
 		return text('Not found', { status: 404, headers });
 	}
 
-	if (!state.prerendering?.fallback && !manifest._.prerendered_routes.has(decoded)) {
+	if (!state.prerendering?.fallback) {
 		// TODO this could theoretically break — should probably be inside a try-catch
 		const matchers = await manifest._.matchers();
 

packages/kit/test/apps/basics/src/hooks.server.js

@@ -1,3 +1,4 @@
+import { building, dev } from '$app/environment';
 import { error, isHttpError, redirect } from '@sveltejs/kit';
 import { sequence } from '@sveltejs/kit/hooks';
 import fs from 'node:fs';
@@ -136,6 +137,15 @@ export const handle = sequence(
 
 		return resolve(event);
 	},
+	async ({ event, resolve }) => {
+		if (!dev && !building && event.url.pathname === '/prerendering/prerendered-endpoint/api') {
+			error(
+				500,
+				`Server hooks should not be called for prerendered endpoints: isSubRequest=${event.isSubRequest}`
+			);
+		}
+		return resolve(event);
+	},
 	async ({ event, resolve }) => {
 		if (['/non-existent-route', '/non-existent-route-loop'].includes(event.url.pathname)) {
 			event.locals.url = new URL(event.request.url);