Lock-free one-sided RDMA transfer of particles from rank A to rank B’s Handler. Rank B executes no code during the entire operation. Dashed blue arrows denote one-sided reads (data flows from B’s memory to A); solid green arrows denote one-sided writes (A deposits data into B’s memory). The sender reads the remote [head, tail] counters (1), writes the particles contiguously into the ring buffer at the tail position (2), and atomically increments the remote tail via FetchAndAdd (3). No lock is required because each Handler has exactly one sender (SPSC). Highlighted cells show the newly written data. If the buffer is full at step (1), the reallocation protocol (Section 3.5) is invoked before retrying.