Two issues found by the diagnostic sweep in #292:
1. Profile double-count in pipe_layer_sparse: the outer t_emm span wrapped
both the shared-expert GPU dispatch AND the moe() call, but moe()
self-times its own t_emm internally (6 accumulation sites). Routed-expert
matmul was counted twice -> accounted > elapsed -> 'other' went negative,
and expert-matmul showed an inflated ~120s. Fix: split into two narrow
spans around only the GPU work moe() does NOT cover (shared-expert
dispatch, routed upload+add), letting moe() self-time as all other
callers already do. Verified: 'other' now positive (14-17s),
expert-matmul realistic (5-6s).
2. MTP blanket-disabled under CUDA (g_draft=0 when g_cuda_enabled). This
was a conservative guard from #163 before the root cause (cold-expert
fused-pair + IDOT kernel divergence) was fully diagnosed. GPU-resident
experts have no divergence; the cold subset still does but achieves
30-50% acceptance anyway (matching non-CUDA builds). Add COLI_CUDA_MTP=1
opt-in so users can test speculation under CUDA. Default unchanged.
Verified: COLI_CUDA_MTP=1 -> MTP ACTIVE (draft=3), 44% acceptance,
3 forwards for 8 tokens (vs 7 without MTP).
Refs #292#163
woolcoxm
78c675eb8b