A grant verdict is read from a 400 body by exact code, never from a 401, a
5xx or a 2xx. A 2xx that is not an object with a non-empty string
access_token and no error is refused as provider_body_not_token_set, so a
malformed success keeps the tokens and surfaces as the typed 502 for every
provider, rotating or not. A refresh answer without expires_in stores the
expiry as unknown rather than keeping the already-due one; an unknown expiry
is never due, so the next resolve does not refresh again.
Pins Soul's three surviving mutants: substring code match, the dropped
expiry rule, and the snapshot refresh token on a non-rotating provider.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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