[AMD-yanfeiwang]

Motivation

The DeepSeek-V4.1-Flash monokernels refuse every PD server today: the target and DSpark draft specs do not declare PD_DISAGGREGATION, so --enable-amd-monokernel on a decode server stops with "PD disaggregation is in use and the spec does not accept it". #67 enabled MoRI PD decode for DeepSeek-V4-Pro; this does the same for V4.1. SGLang serves V4.1 DSpark PD over MoRI since sgl-project/sglang#42457.

Modifications

• deepseek_v41/spec.py and deepseek_v41/draft.py declare PD_DISAGGREGATION.
• _config_disable_reasons refuses a prefill server and transfer backends other than MoRI, with the same reasons as V4-Pro.
• SGLANG_READS pins disaggregation_mode and disaggregation_transfer_backend.
• A unit test covers the gate; the README's MoRI PD note names both models.

The kernels and their layouts are unchanged. They run decode and DSpark verify steps only, so all the state they read (paged SWA KV, compressor states, index keys, the draft's KV) lives in SGLang's own pools, which MoRI fills on the decode server.

With a per-node shared Engram host table, decode also needs #65. Both peers must leave SGLANG_HIP_DSV41_INDEX_K_PAGE8 unset: it changes the index keys' bytes but not their size, so SGLang's PD handshake does not catch a mismatch (the README says so).

Accuracy Tests

DeepSeek-V4.1-Flash + DSpark (block size 5), 1P1D on one MI355X node over MoRI with SGLANG_RAGGED_VERIFY_MODE=static: prefill without monokernels at the decode's TP. TP2 keeps the Engram tables in per-rank host memory on both peers (--engram-config '{"placement":"cpu"}'), as the AgentX TP2 recipe does; on GPU they leave TP2 no room for the KV cache. lmsysorg/sglang-rocm:v0.5.22-rocm10-mi35x-20261028 running SGLang main. GSM8K is sglang.test.few_shot_gsm8k with 1319 questions, sent through the PD router.

decode	TP	--enable-amd-monokernel	startup	parallel 64	parallel 8	DSpark accept length
main	any	yes	refused: PD not accepted	-	-	-
this PR	4	no	serves	0.889	0.908	3.39
this PR	4	yes	serves; target and draft kernels built on all ranks	0.895	0.915	3.39
this PR	2	no	serves	0.908	0.904	3.37
this PR	2	yes	serves; target and draft kernels built on all ranks	0.904	0.906	3.38

The monokernels run verify steps of up to 8 requests, so parallel 8 runs every verify step on them; at parallel 64 most steps are wider and take SGLang's own path. The spread matches run-to-run nondeterminism. Without PD, on the same image, the monokernels score 0.904 to 0.909 at parallel 64 and 0.903 to 0.914 at parallel 8 across Engram table placements.

CPU, same image: test_deepseek_v41_spec.py passes, including the new PD test, and so does the deepseek_v41 contract. The two minimax / minimax_m31 contract failures are the same on main.