FEED.TAIL
Return a shard's current feed generation and next offset.
FEED.TAIL shardComplexity
O(1) on a single shard
Complexity and compatibility are read out of kevy's implementation, not copied from Redis's reference. Several genuinely differ.
Redis compatibility
kevy only
kevy has this; Redis does not. nearest is INFO replication's master_repl_offset, which is not a resumable per-shard CDC cursor