Constant CACHE_SLOTS 

pub const CACHE_SLOTS: usize = _; // 512usize

One-time keys the slice cache can hold (ring size): 32 batches of 16.

Why 32 batches: a key cannot be spent until its batch certificate returns. The Ed25519 core reaches one signature per ~758 cycles only with ~32 requests in flight, each taking ~25,000 cycles, so roughly 25 batches per slice wait in the cache at the full rate. See sustained, section 4a.