Function mismatch_excluded_count 

pub fn mismatch_excluded_count(unfiltered: i64, kept: i64) -> i64

unfiltered - kept, clamped at zero – the count of rows the audience-mismatch predicate excluded from this partition’s materialization. Pulled out as a pure function so the arithmetic behind MetadataPartitionSpec::write’s warn!/imetric! pair is unit-testable directly. The clamp guards kept > unfiltered, which the single atomic count query behind both values should never produce.