The redis `options` block always set `cluster`, so in Sentinel mode Predis
built a cluster client and fired CLUSTER SLOTS at the sentinels ("No
connections left in the pool"). Omit the cluster option entirely when
REDIS_SENTINELS is set — array_filter drops the null while keeping
persistent => false. A single Redis is unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>