In my first question, I'm referring to exposing functionality from the ACP client to the agent. Imagine an IDE ACP client which wants to expose language refactoring to the agent, for example - I can't think of a better example for something more like Toad. As far as I know the protocol doesn't expose a way to inject tools into the agent from the ACP client.
The ACP protocol supports MCP. That would be how the client provides additional functionality for the agent. There's no UI in Toad for that yet, but there will be in a future update.