I love the idea! But to be true to the original, shouldn't the message be self-propagating?
> [...] header that can be transmitted from server to server [...]
How so? In HTTP, there's always one client and one server. Am I missing some way to make this sticky or self-propagating, e.g. browsers or other clients that will cache received headers and then send them to other servers?
There isn't, it's just the people in the loop who can make it self propagating. But then, so did they in the original clacks.