API rule join syntax for "sharing" records with other users?

[j6k4m8]

Hi team, wondering how you'd approach this query that (I believe) needs an aliased join. Very hard to debug these rules (requires an edit and then running a few queries as a test suite) so hoping you might have some insight!

Here's a super simple MVP schema to illustrate; Users write Storys and collect them in Books.

Story
    text:    string
    author:  →User
    book:    →Book

User
    id
    username

Book
    owner:   →User

Here, a user is allowed to edit any Story for which they are an author. Fine, easy:

-- Story permission:
@request.auth.id = author.id

Now they want to invite some collaborators. The best way I can think of doing this (for arbitrary, large number of collaborators) is a separate collection that stores the permission. (i.e., I'd rather avoid a list of relations, since I think that's an anti-pattern here?)

EditPermission:
    book_owner: →User
    book:       →Book
    grantee:    →User

In this toy example I want any user who has been granted permission to a book to be able to edit the constituent stories.

-- Story permission:
-- I am the original creator,
(@request.auth.id = creator.id) 
||
-- Or I have been granted permission to a book:
???

It seems that this is a new feature with the @collection and aliasing capabilities, but I absolutely cannot decode the documentation here nor the answer here for this use-case. Hopefully some help here will aid other users in a similar situation :)