Spec-v2 decode was paying unnecessary scheduler-side copy and replay costs: hidden states were copied back to CPU even when not requested, overlap result D2H ran on the forward stream, and draft graph replay issued several small copies separately.
Port the focused upstream optimizations without taking the larger spec-v2 relay refactor: gate hidden-state D2H on return_hidden_states, run result copies on copy_stream with pinned async D2H, use stride arange for draft select_index, and group small draft graph replay copies while keeping the large hidden-state DMA copy separate.
Constraint: Current branch carries local GLM/NSA/PD/CP changes, so upstream spec-v2 large refactors are not safe to cherry-pick wholesale.
Rejected: Cherry-pick upstream spec-v2 relay/dataclass refactor | too broad for this performance fix and conflicts with current branch structure
Rejected: Copy hidden states unconditionally | default chat output does not consume them after draft extend
Confidence: medium
Scope-risk: moderate
Directive: Keep result-copy lifetime tied to copy_done; do not move copy_to_cpu back onto forward_stream without measuring decode throughput.
Tested: local py_compile for changed production files and new test
Tested: local git diff --check
Tested: remote g0034 cjy-glm5-new as ubuntu on /sgl-workspace/sglang-tai: pytest -q -p no:cacheprovider test_generation_batch_result_copy.py test_eagle_worker_v2_cp_hidden.py test_spec_utils.py
Not-tested: full two-node decode throughput A/B after restart
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