@faust's Laborer: I'm skimming through the discussion. I hope my comments on this are not unwelcome. What if we say that cost-increasing happens before cost-reduction, as a general rule? I'm not too versed with strange costs (Wayfarer mostly), but this seems like it should solve problems.
I guess it's not my card / not my call, but picture what this looks like in terms of the dominion dot games log - all the sudden you're inserting events before the card is played. Likewise Gubump's proposal - it creates this weird inconsistency where the whole turn needs to be evaluated in one go (despite not being complete),
You don't need to evaluate the future. You only need to evaluate everything that's happened prior in the turn...just like you have to do with +Actions, +
, and +Buys, among other things.
you do if you play enough cost reduction and then play cost increases. Everything else does not require this evaluation filter of "is the cost less than zero? if so, its now zero, but if you increase the cost, it was not presently zero"
Lets consider possibly the only canon example we have for what I'm describing vs what you're describing: poor house and wot chameleon, plus some source of coins on action cards.
Like a moron, I played two peddlers before drawing into my poor house. I've got $2 at the moment. Lets say other than that, I've got a hand full of Copper - 4 coppers, one poor house.
I play Poor House using chameleon, draw four cards (lets say it was a Bad 4 cards - all curses - unhelpful) and reveal my hand - four coppers there. How much money do I have at the moment? $0. $2 - $4 => $0.
Now lets play our treasures. I say we end up with $4 - we were at $0, each one contributed $1.
Your reasoning on this puts us at $2 - we were secretly at $-2 (filtered to appear at $0 before more coins were present) but then played 4×$1 worth of treasures. But we know that's wrong.
I don't see why costs should work differently here - you evaluate things in the order they're played, once you hit a floor, that's the new value.
Likewise, we know that order-of-treasures does matter with things like Bank and Fortune - we can't insert the +$ amounts before all the -$ amounts in the order things are played - time travel evaluation is not how the game works. Again, cost adjustment should be consistent with every other tool we've got.