Constant BATCH_MAX_ITEMS 

pub const BATCH_MAX_ITEMS: usize = 1000; // 1_000usize

Default upper bound on items in a single batch request. Server backends enforce this before any SQL runs and surface CoolError::Validation on the outer Result when exceeded. The cap is identical for all five batch operations; deviating per-op would invite footguns where batch_get accepts a list that batch_create of the same length rejects.