CP shared-KV prefill batching can present multiple requests to HiCache write-through in one forward. Keeping host free-room admission per request causes repeated small L2 evictions and defeats the free-room policy, while request metadata and radix attachment still need per-request ownership.\n\nThis change adds a batch prepare path that aggregates required host tokens by CP owner lane, performs one host admission/eviction step for the batch, and then reserves/submits each request independently. SessionAwareCache and the scheduler prefer the batch API when available.\n\nConstraint: Radix nodes, host slots, draft slots, rollback, and ack semantics remain per request.\nRejected: Merge reservations or radix nodes across requests | would complicate rollback and writing_check ack ownership.\nRejected: Add collective synchronization for host admission | local owner-lane logic already provides deterministic capacity accounting.\nConfidence: medium\nScope-risk: moderate\nDirective: Do not reintroduce per-request host free-room eviction in the scheduler path without profiling host-full workloads.\nTested: local py_compile for touched Python files\nTested: remote g0034 docker PYTHONPATH=python python -m pytest -q test/registered/unit/mem_cache/test_cp_hicache_metadata.py => 117 passed, 5 warnings\nNot-tested: full ETE bs>1 HiCache run under production traffic
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