custom bytecode protocol, length first? Command first? Guidance?

[jnz]

Mostly got side tracked here because I mentioned RADIO, but that's already encapsulated. What isn't is that I'll get multiple radio packets, so while each is confirmed itself, I didn't have a way of putting them all together.

I would start with a variant of the Intel Hex Protocol:
This protocol is pretty busy so it may not be workable or it would need to be stripped down:
But, yes, there should be a record length at the beginning.  It is another question if there should be a SOF character ahead of that - Start Of Frame - or just the ':' in the Intel protocol.

rstoufer won with a link above. I modified that a serial packet protocol to be included in first radio packet, so now I have a CRC for multiple individually-confirmed packets, total length, source and dest which could be useful later.