I'm not sure I understand the use case you're talking about my response may be ill-informed, but:

1) Having this code redirect back to the third party auth pipeline is a hard requirement for correct operation of third party auth. We're only partway through the pipeline at this point and if we don't resume it you'll end up on the dashboard but in a state where you've violated important invariants. You'll get all manner of insane behavior, including breaking management of linked accounts (coming in a PR I've written but not yet sent out).

2) In the workflow you're talking about, would someone both be redirected through the login workflow and in a third-party-auth pipeline? Unless they are also in a third-party-auth pipeline, we won't override the pre-existing value.

BTW, no tests broke with this change. I'm not saying that justifies a breaking change and I'm of course happy to understand the use case you're talking about better and update the code if necessary. I just wanted to point out that some tests may be missing/broken.