mismatchKey

True when a different public key has arrived for this node than the one on file.

Two shapes, because the app used to record a mismatch by overwriting the stored key with ERROR_BYTE_STRING. It now keeps the key and clears keyMatch instead — firmware drops the NodeInfo outright rather than overwrite, so destroying the trusted key handed any mesh or MQTT peer a way to break PKC direct messages to a contact. Rows written before that change still carry the sentinel, so both still read as a mismatch.