Thanks for the continued patience on this one folks! The team is actively looking into this behavior with the 401s on cart endpoints, in particular with 3.89.0 but I’ve also passed on how downgrading hasn’t always resolved for everyone.
In the meantime, you should be able to get unblocked by using the preview URL instead of localhost for your development loop, or by downgrading to CLI 3.88.0 if you strictly need the local server (this has worked for many, but not everybody who tried it).
I’ll drop another note here once I have more news to share from the team on the fix.