* Studio: enable MTP for sub-3B Gemma separate-drafter GGUFs
The sub-3B auto-drop to ngram-mod was tuned for an embedded draft head
(Qwen), whose per-token cost regresses below 3B. Gemma ships the head as a
separate root mtp-*.gguf drafter, a tiny standalone model that is cheap
enough to win below 3B: B200 Q4_K_XL bench, draft-mtp n=2 vs spec-off,
gemma-4-E2B (2B) = 1.21x (accept ~0.65) while ngram-mod is 1.00x.
Exempt a separate drafter from the sub-3B gate everywhere the threshold is
applied: the resolver (_mtp_too_small), the auto-fit VRAM reserve, the
drafter auto-download decision, and the reload-skip mirror via a
has_separate_drafter flag on _auto_mode_drops_mtp. Embedded sub-3B heads
(Qwen) still drop to ngram-mod. A drafter the binary cannot build (older
prebuilt, or a CUDA kernel limit) still aborts the spawn and the load
retries once without speculative decoding.
Adds the full Qwen3.5 + Gemma-4 (regular and QAT) auto/off/forced resolver
matrix, plus explicit sub-3B exemption tests.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Always compare the separate drafter in the reload-skip mirror
The sub-3B wrapper around the drafter compare could skip it when the drafter
was deleted out from under a running sub-3B server (detected None, stored set),
leaving a stale launch. The resolved-path compare is cheap and already handles
every case, so drop the _auto_mode_drops_mtp guard (and its now-unused imports)
and always compare when the mode can use a drafter and the user does not own
--spec-type. Addresses review feedback on #6191.
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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