MAX_MESSAGE_LENGTH

Largest text message (UTF-8 bytes, not characters) that survives the send path.

Constants.DATA_PAYLOAD_LEN is 233, and CommandSenderImpl.sendData applies it to the whole encoded Data proto via Data.ADAPTER.isWithinSizeLimit, not to the payload field alone — so the text budget is 233 less TEXT_DATA_ENVELOPE_BYTES. Checking it here returns InvalidArgument before the send path runs, so an over-long message is never written to history.