Curious … what exactly is a cached subrequest here? Thanks!!
This is covered in the FAQ in the workers documentation:
Will my Worker’s response be cached by Cloudflare?
No. Workers are applied to requests before they reach Cloudflare’s cache. This means your worker’s responses are not cached. Any subrequests they make using the Fetch API will be able to utilize the cache, though. This even includes requests to sites that are not powered by Cloudflare, as long as the remote server returns appropriate caching headers.
Meaning that if your worker makes a subrequest, it will first check whether the response is already in cache.