Xcode 15 performance tests ignore baseline

I'm trying to write performance tests with Xcode 15, but it's not working: even though setting a baseline seems to work (baseline data files are created), Xcode seems to ignore that baseline altogether whenever the test is run. As a result, performance tests never fail, no matter how bad performance gets.

The source editor persistently displays a “No baseline average for Time” message.

Has anyone else encountered this? Figured out how to sidestep the issue?

Of note, the issue is easily reproduced: create a new (macOS in my case) app project with tests, add a dummy performance test; run the test once and save its baseline, and despite this subsequent tests will always succeed, even if you significantly slow the dummy test down.

(I've filed this as FB13330139)