Function fuzzed_biome_at_block 

pub(crate) fn fuzzed_biome_at_block<F: FnMut(IVec3) -> u16>(
    biome_zoom_seed: i64,
    pos: BlockPos,
    quart_biome: F,
) -> u16

Single-shot fuzzed biome lookup at a block position. Matches vanilla’s BiomeManager.getBiome(BlockPos): the block is shifted by -2, snapped to the enclosing quart cell, and the winning biome is chosen from the 8 corners of that cell by get_fiddle-perturbed squared distance.

quart_biome returns the unfuzzed biome at a quart-coordinate — typically biome_sampler.sample(qx, qy, qz).id().

Used by carver top-material lookups where a simple unfuzzed lookup would differ from vanilla at the quart-cell boundaries.