Hi @andrew.hyte
Welcome to the Auth0 Community!
Thank you for posting your question! To address your questions, while post-registration action is by design meant to be triggered only by the Database or Passwordless connection, post-login action should be triggered by the social connection.. The proposed scenario is commonly solved by account linking. You can read more on how to do it here → https://auth0.com/docs/manage-users/user-accounts/user-account-linking/link-user-accounts. In the Action Template Library, there’s already a boilerplate for the account linking that you can use.
Thanks
Dawid