A fallback candidate can itself carry a stale credential (e.g. an
expired ANTHROPIC_TOKEN picked up by _try_anthropic). Its 401 previously
propagated out of the fallback call site and aborted the auxiliary task
— for compression: a 60s cooldown + context marker while the session
kept growing past the context cap. Live case: mattalachia debug dump
(Jul 2026), Codex timeout → Anthropic 401 x5 → 296K 'Cannot compress
further'.
Now each fallback candidate call is wrapped: on auth error, refresh the
candidate's provider credentials and retry once; if unrefreshable, mark
the provider unhealthy and walk the discovery chain again so the next
viable candidate serves. Sync + async paths. Non-auth errors still
raise unchanged.
d42e9b1788