Constant MAX_CHECKPOINTS 

pub const MAX_CHECKPOINTS: usize = _; // 429_496usize

The maximum number of checkpoints a valid BlockLocators can ever contain: one checkpoint every CHECKPOINT_INTERVAL blocks, up to the largest height the wire format can express. pub so callers outside this crate - e.g. a message-size cap on whatever carries block locators - can size themselves against this bound instead of restating it.