Now that we're exposting this, we're essentially exposing ProviderSelectionResult as a public type that someone might use. So we should look at this flow a little more critically.

• We use -1 to signal that a new dataSet needs to be made, but we could also just omit it for that case I think.
• The type has a bizzaro isNewDataSet that's not used anywhere. Let's remove that.
• isExisting is only used for the callback, but also is now overloading our use of -1 in dataSetId, so we don't really need it now either
• The type really is a combination of Provider+DataSet (which is what a Context is supposed to be structured around), so how about we rename it.

Here's an interesting option, make it an "intent" for how we want the context to be:

  interface StorageContextIntent {
    provider: ProviderInfo
    dataSetIntent:
      | { action: 'create', metadata: Record<string, string> }
      | { action: 'reuse', id: number, metadata: Record<string, string> }
  }

Simple variation that's not to different to now:

  interface ProviderDataSetSelection {
    provider: ProviderInfo
    dataSetId?: number  // undefined = needs creation
    dataSetMetadata: Record<string, string>
  }

But I think I like the explicit descriptiveness of an intent.

I was planning to make this method private