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- Buffer::sync no longer drops non-same-GPU-id peers in low_latency_mode. DeepEP's original filter was safe because its LL path used NVSHMEM; this port drives LL via PortChannel so the kernel indexes port_channel_handles[local_expert*num_ranks + dst_rank] for every dst_rank. All peers now get a real memory/connection/semaphore/port channel entry. - Add test/python/ext/ep/test_low_latency_multirank.py (LL dispatch+combine functional round-trip, BF16 only). Works cross-node in DeepEP's 1-GPU-per-node topology. - Known limitation documented in src/ext/ep/README.md and the test docstring: intra-node 8-GPU LL currently hangs because every peer transfer routes through the CPU proxy over IB loopback between distinct HCAs on the same host, and (separately) CudaIpcConnection::atomicAdd is a 64-bit op which mis-aligns the 32-bit rdma_recv_count slots when used for same-node peers. Proper fix needs a mixed-transport LL variant (MemoryChannel for same-node, PortChannel for cross-node) or 64-bit counters.