The local expires_in countdown killed OAuth sessions with a bare
"Session expired" before the backend poller's enriched message (Portal
sign-in stalled in the opened tab, retry/API-key fallback) could reach
the UI, and the desktop onboarding poller had no local expiry at all —
a dead session polled forever. Both surfaces now lapse with guidance
naming the common cause, prefer the backend error_message when it has
one, and keep polling when the backend still reports pending (clock
skew).
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