W3 needs batch-size>1 extends to use packed valid tokens while preserving per-request page boundaries. The local out_cache_loc planner now validates against the batch plan's request lengths instead of the first request's scalar split metadata, then reuses the existing batch split helper to produce this rank's logical/physical cache locs.
Direct-write failures inside the CP shared-KV contract now fail fast instead of silently falling back to legacy index/MLA stores. This exposes allocator, owner-lane, page-alignment, and shape-contract bugs early for both bs=1 and bs>1.
Constraint: bs>1 batching must not pad short requests to the longest request; only per-request page-boundary padding is allowed.
Rejected: Keep bs=1 compatibility fallback | it hides CP shared-KV contract violations and caused repeated slow-path ambiguity.
Rejected: Pad batch to max request length | wastes compute and complicates cache validity for short extends.
Confidence: high
Scope-risk: moderate
Directive: CP shared-KV contract errors should stay fail-fast; do not reintroduce silent direct-write fallback without ETE evidence and explicit warning semantics.
Tested: Remote g0034 py_compile for utils.py nsa_indexer.py forward_mla.py
Tested: Remote g0034 PYTHONPATH=python pytest test/registered/unit/layers/test_nsa_cp_utils.py -> 43 passed
Tested: Remote g0034 PYTHONPATH=python pytest test_nsa_cp_utils.py test_cp_shared_kv_layout.py test_cp_shared_kv_runtime.py -> 170 passed, 2 subtests passed
Not-tested: Full ETE bs>1 serving run with live traffic
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