fix(nextjs): improve auth() error message to mention infrastructure failures

Author: jacekradko

.changeset/improve-auth-middleware-error-message.md

@@ -0,0 +1,5 @@
+---
+"@clerk/nextjs": patch
+---
+
+Improved `auth()` error message when `clerkMiddleware()` is not detected to mention that infrastructure issues (e.g. edge runtime errors or platform outages) can also cause this error.

packages/nextjs/src/server/errors.ts

@@ -27,6 +27,7 @@ export const authAuthHeaderMissing = (helperName = 'auth', prefixSteps?: string[
 - ${prefixSteps ? [...prefixSteps, ''].join('\n- ') : ' '}clerkMiddleware() is used in your Next.js ${fileReference} file.
 - Your ${fileReference} matcher is configured to match this route or page.
 - If you are using the src directory, make sure the ${fileReference} file is inside of it.
+- If your ${fileReference} file and matcher are configured correctly, this error can also occur if the ${fileReference} failed to run on this request (e.g. due to an edge runtime error or platform outage).
 
 For more details, see https://clerk.com/err/auth-middleware
 `;