fix(routing): incorrect assumption when loading the middleware

.changeset/nasty-trains-invite.md

@@ -0,0 +1,7 @@
+---
+'astro': patch
+---
+
+Fixes a regression that was introduced by an internal refactor of how the middleware is loaded by the Astro application. The regression was introduced by [#11550](https://github.com/withastro/astro/pull/11550).
+
+When the edge middleware feature is opted in, Astro removes the middleware function from the SSR manifest, and this wasn't taken into account during the refactor.

packages/astro/src/core/app/types.ts

@@ -68,7 +68,7 @@ export type SSRManifest = {
 	serverIslandNameMap?: Map<string, string>;
 	key: Promise<CryptoKey>;
 	i18n: SSRManifestI18n | undefined;
-	middleware: () => Promise<AstroMiddlewareInstance> | AstroMiddlewareInstance;
+	middleware?: () => Promise<AstroMiddlewareInstance> | AstroMiddlewareInstance;
 	checkOrigin: boolean;
 	// TODO: remove experimental prefix
 	experimentalEnvGetSecretEnabled: boolean;

packages/astro/src/core/base-pipeline.ts

@@ -109,7 +109,10 @@ export abstract class Pipeline {
 	async getMiddleware(): Promise<MiddlewareHandler> {
 		if (this.resolvedMiddleware) {
 			return this.resolvedMiddleware;
-		} else {
+		}
+		// The middleware can be undefined when using edge middleware.
+		// This is set to undefined by the plugin-ssr.ts 
+		else if (this.middleware) {
 			const middlewareInstance = await this.middleware();
 			const onRequest = middlewareInstance.onRequest ?? NOOP_MIDDLEWARE_FN;
 			if (this.manifest.checkOrigin) {
@@ -118,6 +121,9 @@ export abstract class Pipeline {
 				this.resolvedMiddleware = onRequest;
 			}
 			return this.resolvedMiddleware;
+		} else {
+			this.resolvedMiddleware = NOOP_MIDDLEWARE_FN;
+			return this.resolvedMiddleware
 		}
 	}
 }