Sinclair is in a different place than the two of you are.
Your wife is testing the waters with you. She is interest in YOU. There is no need to second guess that. Take her at face value, and if/when you have a new reason to distrust, then you check that out if you want to.
The boundary/ultimatum is the AFTER THE LAST RESORT TECHNIQUE. You are not there.
Go with your own goal Sinclair.
Everyone here, including me, has an agenda when they post and they have their own perspective when they post. I make no apologies that my agenda is to support your goal to save your marriage.
You are the only person with the knowledge of your own relationship. You can only show your own perspective here, but the more you test your solutions, think about what is her perspective of your relationship is as well.