How to extend TypeScript interfaces of a dependency

I have a main TypeScript project distributed as a package that can be enriched by plugins (which are just other TypeScript packages).

My main project exposes an API with a definition like below

class Dealer {
    public buyCar (model: string, options: any): void {
        // ...
    }
}

So let's suppose the main project allows to buy cars from a dealer, and that the plugins can add new car models available to buy. How can I extend the buyCar definition from the plugin package in order to add more specific types?

Something like

class Dealer {
    public buyCar (model: "Toyota", options: ToyotaOptions): void;
}

I know I can do this from the main project, but the point is that the main project shouldn't be aware of the plugins, so plugins must extend the interfaces.

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