Your length-prefixed message frames represent a distinct serialization scheme that provides external framing for embedded messages; it’s a standalone format, an

Your length-prefixed message frames represent a distinct serialization scheme that provides external framing for embedded messages; it’s a standalone format, and you can use whatever frame header you want without worrying about collision. The only issue is if you were to ship a “protobuf” library that emits/consumes your (very much not protobuf) framing format. Also, a 64 bit frame length would only be 8 bytes, not 64 :-)