@ngrx/signals Store methods in separate file

I'm just starting to learn ngrx signals and one thing that struck me is that a "store" file could become quite large, quite quickly so ideally I would like to break it into separate parts.

Below is an example of how I might split out the "withMethods" factory but I cannot work out what the type of "store" should be in the bookMethodsFactory function and how I can avoid a circular dependency?

import { inject } from '@angular/core';
import { patchState, signalStore, withMethods, withState } from '@ngrx/signals';

// book.model.ts
export interface Book {
id: number;
title: string;
}

// books.service.ts
export class BooksService {
public getBooks(): Promise<Book[]> {
return Promise.resolve([
{ id: 1, title: 'Book 1' },
{ id: 2, title: 'Book 2' },
{ id: 3, title: 'Book 3' }
]);
}
}

type BooksState = {
books: Book[];
};

// book
const initialState: BooksState = {
books: []
};

export const BooksStore = signalStore(
{ protectedState: false },
withState(initialState),
withMethods(bookMethodsFactory)
);

// book.methods.ts
export const bookMethodsFactory = ((store: ???) => {
const bookService = inject(BooksService);

return {
async loadBooks(): Promise<void> {
const books = await bookService.getBooks();
patchState(store, { books });
}
}
});

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