The rule in question is on page 7

I completely agree that you are correct about the rule here (although it may be the most overlooked Madeira rule, even by experienced players). In practical terms, I'm trying to think of how this would work on BGA.

One thing that should definitely happen is a confirmation to end your turn, in case you want to convert resources or go up/down the windmill. That is the low-hanging fruit here. But that would only address part of the issue. The other part is going up or down the windmill even when it is not your turn.

I have played a fair number of different games on BGA, but of course there are plenty that I have not played. I can't think of any games that allow you to take actions when it is not your turn. Well, to be more precise, I cannot think of any BGA game which doesn't fall into 1 of 2 categories:

- Simultaneous play (like 7 Wonders, 6 nimmt, etc). In this case, everyone is deciding their move simultaneously, but you cannot see anyone's moves until they are all resolved. So you cannot react to something someone else chose.
- Turn-based play where the game is prompting exactly 1 player to make a decision at a time. Only that player is able to make a choice.

For Madeira to allow people to use the windmill outside of their turn, it would be a situation where BGA is prompting one player (whose turn it is) in the regular way. But it would also be prompting every other user about the windmill. Would I be able to end my turn without every other player confirming that they didn't want to use the windmill? And if one player did decide to use the windmill on my turn, then does everyone again have to confirm that they don't want to use the windmill in response to that?

Or would it be a real time thing where if you happen to use the windmill while it's still my turn, fine, but if I finish my turn and you have not done it, then the game progresses and you missed that chance?

I can also see there being issues if I'm trying to use the windmill while you are trying to take your turn. The two actions don't strictly speaking conflict with each other, but you may want to do something different on your turn if you see that I am using the windmill. The game client would have to recognize that the windmill had been used while you were taking your turn, and ask you if you wanted to restart your turn. But what if you wanted to use the windmill only if I decided to do a particular thing on my turn? In that case, the game client couldn't let me undo my turn in response to your windmill use.

I am not sure it's practical to fully implement the rule as written on BGA. I think it should definitely prompt you at the end of your turn to allow you to do any free actions before you complete your turn. Otherwise, careful thought should be given to when a player really would want/need to use the windmilll outside of their turn.

I think the most common case is at the end of the phase C. So I think I would add a prompt to all players at the end of phase C, simultaneously asking them if they want to use the windmill. If everyone says no, the game proceeds. If anyone uses the windmill, then the question is -- do they all use it simultaneously? That obviously isn't how it would work in a physical game of Madeira. Someone would have to declare they are using it, they would use it, and then the others could react. So I think the idea BGA algorithm to cover this would be to do the following at the end of phase C:
1) Prompt all users simultaneously to use the windmill (to go up or down)
2) If no players declare a windmill action, the game proceeds to game D.
3) If one or more players declare a windmill action, then ONLY the player earliest in turn order executes their action.
4) Go to step #1

That way players could continue to react to each decision. This does impose an artificial rule that isn't in the rulebook (player order), but I don't think this works without some order imposed.

Finally, I think you'd want to add a prompt in phase D, right before workers have to be fed, asking users if they want to go up the windmill. The reason this wouldn't be covered by the previous case is because the players may have gained resources from the colonies that allow them to go up the windmill when they could not before. I think the same algorithm I described before would be used, except that only players with the required resources would be prompted.

It's reasonable to not implement rules exactly as written for the online implementation. I can think of several games on here and other similar sites that have slight changes to make it playable online. One example is Hardback, where they changed one of the cards entirely to a form suitable for BGA.

I think adding it at key points (ie phase C) is a good option. Maybe there can be an additional option on the windmill "Ask me about the windmill at the end of my turn", which a player can click on to let the game know they want to use the windmill.

yes, this is tricky bananas, as suggested. It's been addressed the best as possible without a major overhaul.

- There is an undo feature now, and you can trade at that time.
- Also it's possible to trade just before the upkeep phases (phase D).