> There seems to be lack of a single word in English to describe this except the long phrase above. Anyone has good suggestion?

If you mean the request and response message pair, we call it "exchange" [0].

> It goes without saying that this is a hard requirement I have for any API client but sadly most ones I tried always lack some information somewhere.

Both HTTPie Desktop and HTTPie CLI allow you to see the entire exchange. In the CLI, you can use the --verbose flag [0]. In the desktop app, there’s a “Request” tab.

They both also support previewing the request without sending it. The CLI has --offline [1], and the Desktop has a live preview feature [2].

[0] https://httpie.io/docs/cli/what-parts-of-the-http-exchange-s...

[1] https://httpie.io/docs/cli/offline-mode

[2] https://raw.githubusercontent.com/httpie/desktop/master/.git...