To be fair... Chekhov's refers specifically to item or people in some cases that are shown before their use. It's...not really something that applies to a dialog based clue. That's not really the same idea. Also, Chekhos' armoury is typically when too much shit is just thrown out there to the put it's overwhelming to keep track of it becasue they are so many outgoing "guns" that point to different use cases that it's impossible to remember what all of them where and when they'll come back up again. It... doesn't really truly apply in most sense in the way it's being used here.
Remember though, Chekov's Guns DON'T need to be super well hidden or concealed of their true purpose. Most things are technically actually those. After all, it's anything that is used later on, it's revealing something necessarily before it's used whether it be an object...a skill... or a person. It is Foreshadowing attached to an object or a concept that encompasses one. Sorry if misconstruing what you've said Dobbs... that's just the impression I've gotten so far lol.
Anyway that's besides the point.
In regards to the things that Stratos has brought up, My personal rule is try first, ask questions later. I don't mind my Players trying to push something and doing something nuts. In all actuality, If something isn't going to work... I'll either work it into my post and reverse their desired outcome or show them some of the limits in play.
Take for example somethings that have happened in Clash. For example when Exlink's character was fighting Snow my Divine Knight. You'll notice that when Snow attacks early on by hurling a blade of ice at Zagi that the frist and second time it happens... the ice shatters countering the attack. However, later on Snow uses the same attack and yet it overcomes the Fireball.
In my mind as a host, the first two times I allowed Exlink in his post to destroy these fireballs.... and yet later... why did it not work? The answer is simple things have changed. In the first two scenarios I as a Host knew that Snow was underestimating or didn't know the extent of Zagi's((Exlink's character, will be easier to use his name at this point.)) ability. Therefore it's easy to see that under this situation the player's desired outcome would be the effective outcome. Snow is at an information disadvantage ((it can be argued that Zagi was as well however, Ice tends to be weaker to Fire at least in Graterras.)). However, once she knows a rough estimate of his fire's power she changes her strategy. Due to how much more powerful she is and her access to multiple elements, Snow takes this advantage into account and uses her ability to create wind and thunder to wrap the blade of ice in this access element. The bubble of "hard" air or thunder weakens the fireball enough that the Ice dashes right through it this time rather than being destroyed.
As a host, one can react in their post to say, "This is the real outcome" rather than just let the player's outcome be the truth. ((which is where they say oh this doesn't work this way edit that post. DON'T do that. Leave the old post, BUT make sure to explain why it didn't work or why it failed enough that it doesn't seem like an ass pull lol.))
Now, this only works in a host vs Player situation. What about Players against other Players? Well, it gets harder for a host to exactly mediate that however it's still possible. I have a lot less experience here since a lot of the RPs I tend to run are more linear focused and tend to involve me in interactions more often. With the Pokemon based RP we see this. We know those rules to some extent because we have a frame of reference for how things should work ((the anime, games, etc...)) and thus have a canon to pull fromt hat allow us to more easily evaluate without the Host always coming in. We as players can rationalize it out between each other because we know that more easily how to deal with something when it arises. This more or less needs to be what happens in other RPs with this interaction and yet we seem to be dependent entirely on the host at times. ((of course they should ahve last word on any rulings, buuuuuut if we as players can outline things and talk them out and reach a place where it seems reasonable that less work the Host has to figure out on their own etc...))
This is part of the reason for Heartless Souls I'm going to be creating a Spell/Martial Arts index and allow the PLAYERS ((yes you heard that gosh darn correct I said players.)), not only help to create them but to also figure out where they go etc... This way we have our own spells and things and we know Exactly what the do and how they do it. Part of what is needed is the ability for players to feel like they understand the bounds of the world. In a world were those aren't given things go poorly. I noticed this in Graterras original. The Spellcasters had a lot of trouble and didn't care for their characters as much because they didn't know what they could do and how they could do somethings liek progress and get more powerful. THis was a failing on my part as a host because I didn't give them the tools or the understanding to use those tools effectively. This caused a few problems and it showed in a lot of situations. Spellcasting characters I made I knew the rules of the Magic... and they ended up being much more effective and powerful then the PC Spellcasters as a result.
However, I believe that making players be part of the rules system and figuring out the Boundaries along with you as the host makes it more interesting. They are willing to try things more because you give them the free reign to do so. If the Host and Players are comfortable with it one can just canonize that and make it part of how things work, and otherwise you can drop it. Getting the players involved in creating the World with you helps take things along. The Host is another Player after all, they want to have fun too. So, it's okay if the Players help create the world too. After all we're all creating something here. Let's do it together rather than hoarding certain parts lol. Besides it gives many perspectives and thought when it comes to seeing things from multiple angles. The Host's main job would be to make the final judgement call and commit it to the game etc... but everyone could be a part of the others aspects. At least, I think so at the very least. It's why I am making a lot more systems where PLAYERS get to create things rather than giving them pre-fab stuff to choose from and figure out later. If they are already thinking of how they can create abilities and how to balance themselves, it only helps further down the line as they start to try and understand the world and everyone works to a more cohesive picture of that world and how it works.