Module spec 

Qwen3.5 MTP (NextN) greedy speculative decode (research/mtp/MTP-PLAN.md §A/§B/§C/§D).

Greedy spec decode is MATHEMATICALLY EXACT: the accepted+bonus token stream is token-for-token identical to plain greedy generate. This module provides:

• mtp_head_forward (§A, T=1): one NextN draft-token forward.
• decode_step_t (§D.3, T=K+1): batched target verify forward, all-column logits.
• generate_spec (§B): the draft/verify/accept/rollback orchestrator. Cache snapshot/rollback lives in cache.rs (§D.4). The MTP head uses its OWN scratch KV (§D.6), PERSISTENT over the committed sequence (see MtpScratch).

Structs

SpecSampling

Scratch KV for the MTP block (one full-attn layer).

SpecSession

Traits

SpecConstraint

GRAMMAR HOOK for constrained spec decode (lane/constrained-full, 2026-08-03). The engine stays llguidance-agnostic: the server adapts its per-session grammar state behind this trait. CONTRACT (the verify-side truncation rule — token-identical to constrained plain greedy decode): the exactness walk runs UNMASKED first; the hook then (a) truncates acceptance at the first grammar-illegal accepted token, and (b) when the truncation fired or the bonus is illegal, the engine recomputes that slot as the MASKED argmax of the target’s own verify column (an unmasked argmax that is grammar-legal IS the masked argmax — masking only removes tokens — so the common case pays nothing). consume advances the state with each EMITTED token in order; EOS handling is the implementor’s job (skip).