SvelteKit integration hook has the wrong type

[re-xyr]

The SvelteKit hook in @fedify/fedify/x/sveltekit has the type:

type RequestEvent = {
  request: Request
}

type HookParams = {
  event: RequestEvent 
  //     ^ covariant
  resolve: (event: RequestEvent) => Promise<Response>
  //               ^ contravariant
}

fedifyHook(...): (params: HookParams) => Promise<Response>

Notice two points here:

• The RequestEvent type is defined locally and is a subtype of the actual type in SvelteKit
• RequestEvent is invariant in the type of fedifyHook(...), so the type of fedifyHook(...) is not a subtype nor a supertype of Handle, the handler hook type in SvelteKit.

Indeed, TypeScript complains if you try to mark it as a Handle:

import { fedifyHook } from '@fedify/fedify/x/svelte'
import type { Handle } from '@sveltejs/kit'

const handleActivityPub = fedifyHook(federation, makeContextData) as Handle
//                                                                ^^^^^^^^^
// TS2352: Conversion of type '(params: HookParams) => Promise<Response>' to type 
// 'Handle' may be a mistake because neither type sufficiently overlaps with the other. 
// If this was intentional, convert the expression to 'unknown' first.

I suppose the most straightforward way to solve this is to add @sveltejs/kit to devDependencies and then use the actual Handle type from there, something like:

import type { Handle, RequestEvent } from '@sveltejs/kit'

export function fedifyHook<TContextData>(
  federation: Federation<TContextData>,
  createContextData: (
    event: RequestEvent,
  ) => TContextData | Promise<TContextData>,
): Handle {
  return async ({ event, resolve }) => {
    // -- snip --
  };
}

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PS. I see the AI labeler adding more and more labels to my issue every time I edit it. You may want to fix that too!