Web Manifest Problems and Content Security Policy

Ah, stupid me. I've been banging my head on the wall for almost an hour trying to figure out why Chrome is not picking up my web manifest. I recently modified the server to return the strictest possible CSP headers for my use case. I used default-src 'none' but I didn't explicitly set the manifest-src property.

Service worker does not successfully serve the manifest start_url.

So there you go. If you get these kinds of errors in Lighthouse audit be sure to check your CSP headers.