QoS 1: deliver message then send PUBACK. QoS 2: store in-memory pending PUBREL, send PUBREC; on PUBREL deliver and send PUBCOMP. Wire all four PI-packet dispatches (PUBACK/PUBREC/PUBREL/PUBCOMP) in parser. Add QoS2Pending dictionary to MqttHandler for in-memory QoS 2 tracking. 6 new tests for QoS 1/2 flows including full QoS 2 handshake.