Shared KV now relies on page-aligned CP metadata and compute-owner page allocation so persistent MLA KV and NSA index shards can be written by the rank that computed them. The compatibility read path keeps the dense full-view contract for existing topk and attention kernels, but removes duplicated prev/next index materialize, adds optional tai materialize integration, and tightens tests/docs around the fallback boundaries.
Constraint: Decode remains non-CP while prefill CP owns the shared-KV changes
Constraint: Existing attention/topk kernels still expect dense full-view KV/index inputs
Rejected: Change attention kernels to read owner-sharded KV directly | larger semantic change reserved for later phases
Rejected: Merge index K/scale storage with MLA KV storage | would couple topk and attention cache lifecycles before materialize overhead is isolated
Confidence: medium
Scope-risk: broad
Directive: Do not remove fallback logging or debug-gated assertions without reproducing long-context chunked/radix-hit paths
Tested: git diff --check --cached
Not-tested: Local pytest/runtime server verification not run in this commit step per current workflow constraints
5769b63082