The syh branch still passed symm writer metadata into the RAGGED MLA
partial-current compose path. After rebasing the CUDA IPC staging path,
those keyword arguments no longer belong to the runtime contract and would
raise at runtime before reaching the IPC compose implementation.
Constraint: Main-stream CP shared-KV compose should use the measured CUDA IPC staging path; symm remains an experimental/benchmark path.
Rejected: Keep writer-rank arguments behind the symm env | the runtime signature has been restored to the IPC contract and the env-gated symm compose is not the production default.
Confidence: high
Scope-risk: narrow
Tested: python -m py_compile nsa_backend.py cp_shared_kv_runtime.py cp_shared_kv_prefetch.py nsa_indexer.py
Not-tested: Local pytest blocked by missing orjson in this environment; remote CUDA/ETE not run in this step
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