A rejected OAuth token (HTTP 401 'User not found' from Nous Portal, Codex,
xAI…) reached the desktop error card as 'Provider error' with Retry as the
first action, which just replays the same dead credential.
Backend: nonretryable_client_error_result dropped failure_reason /
failure_retryable, so error_surface classified every non-retryable 4xx as a
retryable provider failure. It now stamps the classifier verdict like the
max-retries path, and auth-layer descriptors carry auth_kind
(oauth|api_key, derived from the provider catalog tab) + provider_label.
Desktop: an auth/oauth surface renders 'Authentication error', explains that
the <provider> sign-in expired/was revoked, and offers 'Sign in to <provider>
again' which launches that provider's existing onboarding OAuth flow scoped
to the failed session's gateway profile. Retry stays as the follow-up click.
Re-login to the provider already in use keeps the current model instead of
swapping in the recommended default.
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