Function default_dflash_gamma 

pub const fn default_dflash_gamma(trained_block_size: usize) -> usize

2026-09-25: The DFlash gamma for a drafter of this trained block size, when no --dflash-gamma was given.

The one rule for it: the drafter head resolves its gamma through this, and so do the preflight paths that size pools and reserves from a peeked dflash_config.block_size.

block + 2, because these drafters chain past their trained block. Measured 2026-08-29 on GB10 with Qwen3.8-27B DFlash2 (block 8): gamma 10 was the fastest serve, 63.0 against 56.2 tok/s at gamma 8.

Clamped to MAX_F16_TWIN_DFLASH_GAMMA, so a block-16 drafter lands on 15 (verify width 16, which has a kernel for both h-state dtypes) rather than 18.