Constant SAMPLE_RECORDS 

pub const SAMPLE_RECORDS: usize = crate::constants::K_VOCABULARY_SAMPLE_ELEMENTS; // 64usize

How many records open needs to see to resolve a projection.

The surface’s own sampling constant, reused rather than restated: judging a stream’s vocabulary and suggesting names for a failed key are the same question about the same records, and two constants for one question is how they drift.