Fixed!
Turns out every time the player exits the shop, any available stamps would run their 'apply to card' code! Now they don't!
Gave this a play now that it's fixed and was able to complete a seed, though I did find a couple issues:
1. The logic for goal is having ONE Wild and Wipe stamp, instead of all of each as I believe was intended. (this matters for Minimal accessibility)
2. The first purchase in each shop slot does not send a check, I think this is probably just an off by one, but it's not a blocking issue it just makes the early-game a bit grindier.
3. Combo checks didn't seem to send at the right time - in particular Combo 12 didn't send when I goaled (but 8-11 did), and what I thought was a combo of 11 didn't send any of 8+. Not sure if I wasn't understanding something (does suit matter even for wilds?) or if there is another issue here, but figured it was worth mentioning.
4. There's no logic for Swap Stamps, so you can be expected to grind about 7000 points without any card upgrades. In a solo game this isn't really an issue since you can supplant this with cheap OOL checks on Wipe Stamps, but if this was in a larger game, having something this grindy in sphere 1 is pretty rough.
5. Similarly, the logic for Wipe and Wild Stamps puts all of them into logic at the same time.
6. There's a bug where if you press Space as scoring completes, then it will re-score the same hand (this also iterates on locks/unlocks).
7. You can't use two of the same type of stamp in a row in the shop (without leaving the shop) because the icon doesn't come back.
Ultimately none of these kept me from enjoying a solo seed, and (with logic fixes) I'd happily throw this into a larger async as an extra slot.