NSA spec-v2 draft-extend graph replay was still using host-derived sequence lengths and the draft-decode backend allowlist. That kept NSA on eager draft-extend for spec-v2 and left seq_lens_cpu.max()/list-to-GPU tensor construction on the decode critical path.
This ports the small upstream DSA metadata fixes into the local NSA backend: size the captured graph page table to req_to_token width, use the static captured page-table width for graph replay, split v2 draft-extend from variable-length v1 draft-extend, and decide draft-extend graph support from the prefill-style backend.
Constraint: Current branch does not have the full upstream needs_cpu_seq_lens scheduler/FutureMap infra.
Rejected: Cherry-pick the full DSA fused metadata generation series | too broad and overlaps with local NSA fused metadata-copy code.
Confidence: medium
Scope-risk: moderate
Directive: Do not collapse DRAFT_EXTEND and DRAFT_EXTEND_V2 here; v1 keeps variable accept lengths while v2 must stay graph-static.
Tested: local pytest test/registered/spec/eagle/test_eagle_v2_draft_extend_contract.py -q (19 passed)
Tested: local py_compile on nsa_backend.py, nsa_backend_mtp_precompute.py, eagle_worker_v2.py
Tested: remote g0034 cjy-glm5-new pytest test/registered/spec/eagle/test_eagle_v2_draft_extend_contract.py -q (19 passed)
Tested: remote g0034 cjy-glm5-new py_compile on nsa_backend.py, nsa_backend_mtp_precompute.py, eagle_worker_v2.py
Not-tested: full decode E2E with SGLANG_ENABLE_SPEC_V2=1
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