Avoid Graph API redirect loops but redirect to slugged URL

I've stumbled upon a tricky situation I'm not sure how to solve.

I use the Facebook Graph API to track shares on my web app's articles and display that counter to my users. The API requires that I specify an og:url property to know under which URL to aggregate counts.

My URL structure is as follows:

.../posts/id/slug

The slug is purely cosmetic and optional. If it is later changed (which sometimes happens), I want to ensure:

1. That my users are still redirected to the right page


2. That the share counter isn't reset

To satisfy condition 1, I set up the following redirects:

A) .../posts/id            --> .../posts/id/current-slug
B) .../posts/id/wrong-slug --> .../posts/id/current-slug

To satisfy condition 2, I pointed my og:url to the slugless URL .../posts/id, which is invariable.

But of course, this causes a redirect loop for the Facebook grapher, whether the initial URL was correct (case X) or not (case Y).

Case X:

Start: .../posts/id/slug
   --> .../posts/id        (Because of og:url)
   --> .../posts/id/slug   (Because of redirect)
   --> (loop)

Case Y:

Start: .../posts/id/wrong-slug
   --> .../posts/id/correct-slug (Because of redirect)
   --> (back to case 1)

Any idea how to solve that problem?

The only solution I see at the moment is to remove redirect A), but it makes the URL much less user/SEO friendly.