Function global_beat_is_canonical_kernel 

pub fn global_beat_is_canonical_kernel(input: GlobalBeatValidationInput) -> bool

Validate one candidate before granting its cluster ready.

Beats 0 through 33 require all 64 byte lanes and must not assert last. Beat 34 requires only its low 32 lanes, asserts last, and keeps invalid high lanes zero. Every beat after beat zero must retain the same opaque job ID.