CORS issues are all on you.
I’ve never had a problem like what you describe.
And I also build and publish various extensions.
Hosted test and release are the same when it comes to the domain used for the calls.
My code examples above are from my live extension EBS’s.
CORS issues are all controlled by the EBS and nothing to do with Twitch.
If you rever to local test then the origin will be different.