lf.tune sends the 2-byte {mode,divisor} the firmware requires (was 3 -> EINVARG/0V). t55.writebl packs the 10-byte {data,pwd,blockno,flags} struct with a single bit-packed flags byte (was 12). t55.wakeup packs 5 bytes {pwd,flags}. t55.config is maintained client-side (firmware has no GET). LF_SAMPLING_SET_CONFIG uses send_ng_no_response (firmware never replies). Pre-existing, independent of the rebase.