How can I create a transient assistant with tools? POSTing to /calls with

{ assistant: { tools: [ {type: "endCall" } ] } }

returns an error assistant.property tools should not exist. But posting with "tools:append" e.g.

{ assistantOverrides: { "tools:override": [ {type: "endCall" ] }}

returns an error Cannot read properties of undefined (reading 'tools').