Constant MAX_SIMD_LANES 

pub const MAX_SIMD_LANES: usize = 64;

Lane capacity of the fixed scalar-fallback stack buffers used by the default SimdKernel methods (scan_vector, swap_adjacent, dup_even/dup_odd, and the kernel_helpers scalar emulations). A backend’s SimdKernel::LANE_COUNT must not exceed this, or store_unaligned into those buffers would overflow the stack. The current workspace maximum is 64 (AVX-512 i8, 64×i8); the bound is checked at compile time by SimdKernel::LANE_BOUND_CHECK, so a future wider backend fails to build rather than silently overflowing the stack.