Cancelling a request or model refresh while an OAuth token refresh was in
flight discarded the rotated credential. Providers that rotate refresh tokens
(e.g. Sign in with ChatGPT) had already invalidated the old token, so the next
request failed with refresh_token_invalidated.
The caller's signal now cancels only the wait for the credential lock. Once a
refresh starts, it completes and is persisted, bounded by the refresh timeout.
Request auth and model-list refresh share this path.
Move provider auth and OAuth flows onto pi-ai Models, compose models.json and extension overlays through ModelRuntime, and retain ModelRegistry as an extension compatibility facade.
