Check Handle Available

Whether the editor may offer handle. Advisory, never authoritative.

The answer is a boolean and a coarse reason. It never says who holds a taken handle, because "taken" is the entire answer a client needs in order to pick another one, and the alternative is a lookup service that maps handles to people. Requires a session so that walking the namespace costs an account — see the module docstring on enumeration.

Your own current handle comes back available: true. Opening the editor and pressing Save without touching the field must not be told that you are already using your own name.

A shape violation is a false with reason: "invalid", not a 422. This is called as the user types, and "you have typed two characters so far" is not a client error.