dupe_check in v3 felt like a bit of a hack to me, as it was a rater blunt instrument and iirc would actually throw an exception if a dupe was found. The more configurable civicrm_api3('Contact', 'duplicatecheck') action seems more worthwhile to port over imo.
Thank you for raising an issue to help improve CiviCRM. As you may know, this issue has not had any activity for quite some time, so we have closed it.
We would like you to help us to determine if this issue should be re-opened:
If this issue was reporting a bug, can you attempt to reproduce it on a latest version of CiviCRM?
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