6.1.5 says "This message MUST be syntactically valid." I'm not entirely sure what was intended there, so took a stab at clarifying. In any case as-is that sentence doesn't really seem to say anything useful.
My suggestion assumes that enc is included as part of the ECH in the AAD used with HRR. Given we omit enc from the 2nd ECH as-sent that seems a bit wrong so may need a few more words.
Note that the next bullet talks about using the "emtpy string for enc" - not sure if "empty string" precise enough but if we omit enc from both AAD and ECH (during HRR) we may need align how we describe things.
6.1.5 says "This message MUST be syntactically valid." I'm not entirely sure what was intended there, so took a stab at clarifying. In any case as-is that sentence doesn't really seem to say anything useful.
My suggestion assumes that enc is included as part of the ECH in the AAD used with HRR. Given we omit enc from the 2nd ECH as-sent that seems a bit wrong so may need a few more words.
Note that the next bullet talks about using the "emtpy string for enc" - not sure if "empty string" precise enough but if we omit enc from both AAD and ECH (during HRR) we may need align how we describe things.