The CpSharedKVLayout initialization was gated behind
`if not self.is_draft_worker`, leaving the draft model runner
with `uses_cp_shared_kv=True` but `cp_shared_kv_layout=None`.
This caused an AssertionError in NSAIndexer._filter_shared_index_write
during DRAFT_EXTEND under CP shared KV + MTP.
Move the layout init after the `is_draft_worker` guard so both
target and draft model runners have it available.
ThomasX
3f1e5c5896