EAGLE V2 draft MTP can avoid recomputing NSA/DSA indexer topk across internal draft iterations when the model declares that those indices are shareable. The port follows the upstream narrow contract: store per-forward topk on ForwardBatch, enable reuse only for topk=1, and clear the transient state after draft_forward.
Constraint: topk > 1 reorders hidden rows in select_top_k_tokens, so carried topk indices would no longer match the hidden states.
Rejected: Reuse target-side topk for draft | broader semantic change not covered by the upstream fix or current tests.
Rejected: Skip loading draft indexer weights | separate memory optimization with correctness risk for models that do not enable MTP index sharing.
Confidence: high
Scope-risk: narrow
Directive: Do not enable index_share_for_mtp_iteration without preserving the topk==1 guard and per-draft-forward cleanup.
Tested: python -m pytest test/registered/spec/eagle/test_eagle_v2_draft_extend_contract.py -q
Tested: python -m py_compile python/sglang/srt/speculative/eagle_worker_v2.py python/sglang/srt/models/deepseek_nextn.py python/sglang/srt/model_executor/forward_batch_info.py test/registered/spec/eagle/test_eagle_v2_draft_extend_contract.py
Not-tested: full GLM5 EAGLE throughput/accuracy run
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