- Add cooldown flag to MTP speculative state: after draft rejection,
skip next proposal to force single-token decode for fresh MTP logits
- Root cause: MTP logits are from the last batch position (draft token).
When draft is rejected, next proposal uses stale/wrong logits (13% accept).
With cooldown: proposals only use fresh single-token MTP logits (95% accept).
- Simplified seq_rm fallback: log and continue instead of re-evaluating
- Added debug logging (MTP-DBG, MTP-VERIFY) for acceptance rate tracking
- Results: 95% acceptance rate, 0 restarts, no garbled output on 2048 tokens
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