[None][feat] Support Helix CP with Eagle3

[brb-nv]

@coderabbitai summary

Description

• Known limitation (acceptance rate, not correctness):the Eagle3 draft submodule is built with the TP-repurposed mapping, so its MLA attention doesn't yet do the Helix all-to-all. Final output is correct (the target verify uses correct Helix attention), but draft acceptance may be low until the draft attention is given the CP mapping (mapping_with_cp). This is a follow-up; flagged inhelix.mdand the code.
• Highest-risk areas to watch in e2e:the KV-slot bookkeeping when all drafts are accepted (off-by-one edge), the overlap-scheduler verify sub-branch (Helix+overlap is "Untested" upstream), and CUDA-graph capture withdraft_len > 0under Helix. The verify path and ownership math are the parts I'm most confident in; the draft-loopkv_lenshandling is the part most likely to need iteration.

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[brb-nv]

Closing in favor of #16003.