Indeed. This is precisely the thing I am trying to make work in PbP.
First, we will not be short-circuiting the process, I have seen people try to skip these discussion steps and the game breaks. This is why I said in my interest check post that players needed to be able post (OOC) rather frequently.
In the beginning this can take a lot of back and forth, and takes a while --even at the table. As we learn the game (and our group's style) we will settle into a predictable set of defaults, we will know what sorts of things are Desperate, and what sorts of Actions will have little to no Effect, and will only need a quick confirmation before rolling. The more familiar with the game we all are the faster this process gets.
I will create a resource document about exactly how we will handle rolling here, but wanted to first get players onboard and deal with rules questions before going into detail about PbP and mechanics.
How these things are handled depends a fair bit on the group's preferences, there is some leeway in the rules, but we will be doing what the rules say as much as possible.
Depending on how the group chooses to handle things, there are several steps that can be combined and preempted.
Always, first the player says what their character is doing in the fiction, up to the point things could go wrong (a lot can be done without needing a roll).
Based on the fiction it should be fairly clear what Action they are trying to do. If their Action does not fit the fiction (maybe they described something completely different ("Quickly climb the tower using Finesse", Finesse is not 'quick', Finesse is not 'gross motor', go back and reread the Actions' definitions), or maybe is as silly as trying to "seduce the door" and could not work at all) then we need to have a conversation about the fiction and the GM will decide if they can continue with Zero Effect (still offering the opportunity for them to try and to use the other mechanics to improve their Effect) or if that Action is out-Scaled to the point of impossibility ("the door is immune to your charms, no matter how much you try", "the mob is too large, you will need to first find a way separate them or reduce their Scale") and the player needs to go back and rethink what is happening, possibly editing their post or adding a new post with the adjustment. This can really slow things down, but should not come up very often once everyone gets on the same page about the fiction.
If the Character's Action fits the fiction (it should most of the time... with practice), the player can post OOC saying what they are trying to achieve (don't assume it is clear from the fiction, your motives may be more subtle than your actions) and what they think the Position and Effect are. This statement by the player is very useful, it shows us what they think is happening. If the player says it should be Controlled with Great Effect and we don't see it that way, then, clearly, something about the scene has not been communicated well enough and we need to discuss it. Maybe the GM has a surprise that changes things, maybe the player forgot about some outside influence (mentioned days ago), whatever it is, because the player stated how they though things were, we can easily see that there is a disconnect and address it.
If the player's assumption of the situation (and Position and Effect) is 'correct' then that shows us that we are all on the same page, that things are flowing well. This is the desired state, we should be able to assume the default most times and only need to change things in the exceptional cases.
Hopefully (with practice) the entirety of this conversation is the player stating their desire and suggesting P&E; the GM saying "sounds good roll it"; optionally: the player saying "I push myself/accept Bargain/Trade Position for Effect"; and we are done.
There is also the question of Help. This is always a bugbear in PbP. By the rules Help (from other players) needs to be declared before the roll, but we may ease up on that rule where it makes sense. We don't always want to have to wait for everyone to say "I won't be helping". If, after the roll, you think your character can help, speak up and we can address it, possibly allowing it.
The whole time, while that conversation is happening, all players should suggest Devil's Bargains so the player can decide if they want to take one of them.
To save time we can also discuss potential Devi's Bargains related to the scene we are in, build up a list we can draw from before a roll is called for. That way we don't have to have that whole discussion after the roll comes up.
This was more than I intended to write, but I hope it was helpful. Keep the question coming.