pub const CTX_BITS: usize = _; // 4usizeExpand description
Bits of a key-context index (and of an op lag). The SHA-512 chain lanes (82 cycles each) stretch one key over more 68-cycle periods, so that profile needs 32 contexts; Haraka and BLAKE3 need 16.
A context is the slot of per-key state (seed, nonces, chaining values, commitment words) that a key owns while it is in flight. More contexts cost deeper (but still small) RAMs, so we use the fewest that fit.