Function is_quiet_window 

fn is_quiet_window(files: &[FileHandle], region_sequence: u64) -> bool

Whether the region has written at least as many rows as files hold, and at least one row, since the newest of them was written. Sequences are assigned per row and compaction keeps the inputs’ maximum, so this needs no state. Files written before row counts were recorded have zero rows, so a window holding them is not quiet.