[Feature Request] - Define multiple customised assistants

[ga-it]

It would be very useful to define assistants with custom handles and custom prompts.

This should allow us to call the custom assistant by the handle as we currently do using the [at]assistant and for it to behave in line with its custom prompt.

[edward-ly]

I'm not sure if I understand the value a user-specified handle would bring to the app. Could you provide an example use case where changing the handle would be useful? Or do you just want to change the current default handle to something else?