Typescript and Chrome/web extensions: creating a d.ts file for content scripts' subset of @types/chrome

I'm a novice/intermediate user of typescript, so thanks in advance for any patience and assistance.

Chrome/web extensions' content scripts have access to a very limited subset of extension APIs and I'm trying to create a global.d.ts file to reflect that. Here is my [very] busted first attempt:

export {}

declare global {
    interface Window {
        chrome: Chrome
    }
    const chrome: Chrome // I'll ask a question about this line after this code block.
}

interface Chrome {
    runtime: import('../node_modules/@types/chrome/index.d.ts').runtime
    // I know this is bad syntax, and of course, content scripts' chrome.runtime is 
    // only a subset of the full chrome.runtime namespace, but hopefully this
    // illustrates what I'm trying to do.

    // Other namespaces: storage, dom, i18n
}

I've only done a little work with d.ts files before (I have a separate global.d.ts for the extension service worker context). Can anyone help me understand a few things?

• Does a content-script types library already exist? I didn't see any in DefinitelyTyped.
• Can a d.ts file "import" a part of another d.ts file? I'd rather not copy/paste/rewrite typings that already exist.
• Example, how can I declare a global [window.]chrome.runtime.sendMessage and reuse the chrome.runtime.sendMessage from @types/chrome?
• Conversely to wanting to import parts of @types/chrome, I don't want the rest of the @types/chrome globals/namespaces. @types/chrome/index.d.ts has interface Window { chrome: typeof chrome; } in it.
• Tangential question: Content scripts run in a DOM context (i.e. globalThis is Window), but I noticed that VSCode won't resolve my global if I only do declare global { interface Window { foo: string } }. I either have to reference the global via window.foo or include a separate global variable like above: declare global { interface Window { foo: string }; const foo: string }. Why doesn't VSCode resolve foo when I added foo to Window?

Thanks again!