refactor(daemon): Parameterize provide type assertion

[kriskowal]

This change adds a vestigial second argument to provide that just hints to TypeScript the expected return type, resulting is much less verbose type narrowing. I’ve also advanced provide higher in the flow so it can eat all the forward-reference lint comments.

[rekmarks]

This is a great change. Below, I provide a suggestion and one finding concerning Provide.

[rekmarks]

A couple of things regarding this one. First, I propose we reimplement it as follows:

1. Establish a private type that only exists to map Formula['type'] to the type of the value instantiated by a formula:

type FormulaTypeForValue = {
  endo: EndoBootstrap,
  host: EndoHost,
  guest: EndoGuest,
  worker: EndoWorker,
  // ...
};

2. Replace the ternary chain above with:

export type Provide = <T extends Formula['type'], U extends FormulaTypeForValue[T]>(
  id: string,
  type?: T,
) => Promise<U>;

This has the benefit of being more succinct and partially self-validating since the definition of Provide errors if FormulaTypeForValue does not have a key for every value in the string literal union Formula['type']. (It's still possible for keyof FormulaTypeForValue to superset Formula['type'], but that will cause type errors at the point of use.)

Second, as it happens, Formula['type'] in fact does not include all of the string literals used as the second argument to provide(), specifically the following:

• agent
• hub
• network

I had thought that there was a bijection between "formula types" and "kinds of values that can be provided". I think we should attempt to eliminate this discrepancy if possible. If we don't want to do that now, we can still implement my above suggestion with the following band-aid:

type Providables = Formula['type'] & 'agent' | 'hub' | 'network';
// FormulaTypeForValue modified as necessary
export type Provide = <T extends Providables, U extends FormulaTypeForValue[T]>( /* ... */

[rekmarks]

Just for explicitness:

Suggested change

	const provide = id =>
	const provide = (id, _formulaType) =>

[rekmarks]

LGTM!