Calendar sync retries a revoked Google token forever instead of asking to reconnect #661

When Google refuses a refresh token, its token endpoint answers 400 with error: invalid_grant and a description such as "Bad Request". _extract_error_text_from_payload (backend/services/calendar_service/text_utils.py) keeps only the description, so _classify_sync_failure never sees invalid_grant and marks the account "Needs attention" instead of "Reconnect required". The 15-minute sync and the push sweep then retry the refresh indefinitely, about ten token requests an hour per account. Settings shows only "Bad Request", and the dashboard keeps showing the calendar as it was at the last good sync.

Fix: classify token-endpoint failures on the OAuth error code (invalid_grant, interaction_required, consent_required, login_required, Microsoft's AADSTS invalid_grant included), and keep reconnect-required accounts out of the push sweep and the reconcile after a sync.

Ours