Webhook for two constituents being merged?

We are working on syncing data with our Raiser's Edge database and I wanted to know how we could tell if two constituents were merged into one? I don't see a webhook for this, so I'm not sure how we should deal with it.

Here's how I envision this happening:

User creates new account with unique email - we create a new constituent code for them via the Constituent API.

Later, that same user (who hasn't logged in for a long time) creates a new account with a new email address because they forgot they had an account. We create a new constituent code for them via the Constituent API because we can't tell that it is a duplicate from our end.

Later, in the Raiser's Edge system it is seen that that “new” person is actually a duplicate of a previous constituent (they later enter in the same mailing address), but just with a new email address.

So in Raiser's Edge, that new constituent is merged with the old one.

But now we have a problem in our system, because we have two records for the same person that Raiser's Edge now knows is actually one person.

How do we sync this merging action?

Thanks!