MTP: NextN layer가 있는 qwen35moe 파일에 draft가 없음 (Role::Unused) #30

NextN(MTP) layer를 가진 qwen35moe GGUF 파일(예: Qwen3.8-35B-A3B distill)은 그 layer를 읽기만 하고 쓰지 않습니다(Role::Unused). MTP draft가 없어서 decode가 MTP로 얻을 수 있는 속도를 그대로 놓칩니다.

• 근거: crates/model/src/arch/qwen35moe/roles.rs:173-175(trunk 뒤 layer는 Role::Unused), crates/model/src/arch/qwen35moe/mtp.rs:70, 285(draft와 target 모두 qwen4exp만 받음), spec.rs:180(mtp: Vec::new()). MTP body는 Body38에만 있습니다(crates/app/src/arch/qwen3moe/mtp.rs:16).
• 할 일: qwen35moe target과 draft를 받도록 mtp.rs를 넓히고, Body35에 MtpBody를 붙이고, qwen3 seat에 draft를 연결합니다. 공통 owner는 이미 있으니 모델 쪽 부분만 붙이면 됩니다.

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Checklist

Common first, then the model: the draft's mode and feed have one owner before Body35 attaches.

• The model side reads the NextN layer (in_file, model: a qwen35moe file's next-token layer is described as an in-file draft (#30 M0+M1) #165).
• Lift the draft's walk mode and feed into one owner in crates/gpu. Today each draft layer carries its own copy
  of the same three modes (MtpMode for Qwen3.8, NextnMode for GLM: Eager, Graph, Store) and its own feed type,
  and each MtpBody glue maps the shared WalkMode/Feed onto them one to one (crates/app/src/arch/qwen3moe/mtp.rs
mtp_feed/mtp_mode, crates/app/src/arch/glm5next/mtp.rs nextn_feed/nextn_mode). After the lift, Mtp38, the
  GLM NextN layer and mtp35.rs take the shared types directly, and both glue files lose their mappings.
• Body35's MtpBody glue on top of that: only what the architecture differs in (the head, the hidden width, the
  prompt calls), wired into the qwen3 seat. mtp35.rs (the draft layer on the card) is already on main.
• M2b-1, mainline's MTP step taps as a reference set: the work is on branch q35m2b (closed PR refset, tools: mainline's Qwen3.6 MTP step taps as a reference set #242, head
  a4e71119). Port it onto main in the same round, and fix its open review item first: an existing destination with
  a trailing slash makes the dump installer delete both the old set and its replacement.
• M2b-2: the card's draft step held to the M2b-1 set tap by tap in gate_qwen35moe_mtp.
• First measurement: the acceptance rate on this model, then decode with the draft on against off.