nx_bench_tsv_persist.nx

nx_bench_tsv_persist.nx -- write bench TSV rows to a real file on disk. Sibling to the emit + parse primitives. Closes the final loop: measurement bytes now persist beyond process exit so cross-runner comparison (Nishi.tsv vs llama_cpp.tsv vs vllm.tsv) reads canonical-format rows from disk. V1 ships: nx_bc_persist_open_append(path, path_len) -> fd or NEGATIVE nx_bc_persist_write(fd, buf, n_bytes) -> bytes_written or NEGATIVE nx_bc_persist_close(fd) -> 0 or NEGATIVE nx_bc_persist_row(path, path_len, buf, n) -> bytes_written or NEGATIVE (one-call wrapper: open-append + write + close) Sealed verdict so callers handle disk failures (ENOENT, EPERM, etc.) as structured negative returns instead of as silent zero-byte writes.