which, if its the LLM asking for the result of the locally ran "echo $API_KEY", will be sent through that proxy, to the correct configured domain. (If it did it for request body, which apparently it doesn't (which was part of what I was wondering))

The AI agent can run `echo $API_KEY` all it wants, but the value is only a placeholder which is useless outside the system, and only the proxy service which the agent cannot directly access, will replace the placeholder with the real value and return the result of the network call. Furthermore, the replacement will happen within the proxy service itself, it does not expose the replaced value to memory or files that the agent can access.

It's a bit like taking a prepaid voucher to a food truck window. The cashier receives the voucher, checks it against their list of valid vouchers, records that the voucher was used so they can be paid, and then gives you the food you ordered. You as the customer never get to see the exchange of money between the cashier and the payment system.

(Noting that, as stated in another thread, it only applies to headers, so the premise I raised doesn't apply either way)

Except that you are asking for the result of it, "Hey Bobby LLM, what is the value of X" will have Bobby LLM tell you the real value of X, because Bobby LLM has access to the real value because X is permissioned for the domain that the LLM is accessed through.

If the cashier turned their screen around to show me the exchange of money, then I would certainly see it.