coreMQTT remade in Rust: a complete MQTT 5 client -- the QoS 1 and 2 publish state machine in both directions, the fixed-header codec, every packet a broker can send and every packet a client can send, the MQTT 5 property builders and readers, the connection, the receive loop and the acknowledgements. Twenty-four slices, each diffed against coreMQTT v5.0.2 compiled verbatim, comparing the state left behind and not only the answer: the fixed header over 6,291,456 calls, and a topic matcher whose 39x39 printed grid showed a wildcard filter silently missing a whole class of topic. The differential found a one-byte buffer overflow in the C, by being unable to reproduce it. Zero allocation, no_std, forbid(unsafe). ALL 218 of coreMQTT's 218 functions, counted from the pinned source by a checked-in script.