Verified: TestModelsSayWhatIsNotExposed and TestGroupMemberNotExposedSaysHow
fail on the old code (magpie models and magpie provider og never name
deepseek-flash; magpie groups says only "(not served)") and pass with it.
provider set models= says the same. Taking out a model that isn't
exposed, mixing +/- with plain ids, or leaving none exposed (which would
mean the default list) is an error that saves nothing.
Verified: TestProviderModelsAddsRemovesAndSaysWhatItReplaced fails on
the old code ("+deepseek-flash left [+deepseek-flash]") and passes with it.