Function compute_tick_checksum 

pub fn compute_tick_checksum(
    pool: &DiffPool,
    diff_start: u32,
    diff_count: u16,
) -> [u8; 32]

Compute a Blake3 checksum of a frame’s diffs in the DiffPool.

Hashes each 18-byte WavDiff in the frame’s range sequentially. The resulting 32-byte hash is stored in FrameSnapshot.checksum for bitwise reproducibility verification across edge devices.

Zero allocation — reads directly from the pre-allocated ring buffer.