Well, what it actually says about Debt in the rules is "can be done both before and after buying cards". So: is there a special time between finishing buying cards and starting the end of the Buy phase in which all you can do is pay off Debt
I think this is correct, except that it's not "a special time". It's the same type of time that you had before, after, and between any card buys. Nothing about the game "knows" if you are done buying cards or not. During this window of time, there are a total of
6 5 things you are allowed to do:
1) Buy a card/event/project (but only if you have buys remaining, and no
).
2) Pay off
.
3) Spend a villager.3) End your buy phase.
4) Play a treasure (but only if you haven't bought a card in this buy phase yet).
5) Spend a coffer (but only if you haven't bought a card in this buy phase yet).
Whether you plan on doing 1) or 3) next has no bearing on your current legal choices. You might be done buying cards, you might not be.
Once you chose to do option 3, end your buy phase, the game moves to "at the end of your buy phase", where you no longer have any options except for special ones such as the one granted by Wine Merchant.