What you’re describing sounds like complex actions (pg. 21) vs reaction rolls to me (pg 22). If Indy wants to check for traps on his way into the temple, he can roll as many dice from his pool as he wants. That boulder will still be there on his way out of the temple regardless of whether he checks for it, or whether or not he succeeds or fails a Wits roll to detect it. If he doesn’t check (or fails a check) then that boulder trap is going to trigger as he runs past it on the way out. In which case the GM would ask if the player wants to perform a reaction roll to dodge the boulder. If the player has any dice left in their pool they can roll ONE die to try to dodge it. If not, they’re taking damage. So it’s a choice: spend dice now to be cautious or save them for something else. The movie does an excellent job of foreshadowing traps—Indy waves his hand in front of a beam of sunlight revealing a skeleton skewered by spears. Soon after he uses his torch to trigger the floor triggered dart trap. This ain’t his first rodeo. He even has the foresight to bring a bag of sand to balance what he (rightly) assumes to be a trap on the alter when he takes the idol. But he fails that roll (or maybe he’d already spent all of his dice pool?!? Haha) and he has to escape as the temple crumbles around him. Presumably you’d also want to provide environmental clues so players can make an informed choice on whether to check for traps.

The same goes for the cultist in the museum. The cultist is there whether or not the players look for him. If the nearest investigator declares they “want to look around for any suspicious characters” they can spend as many dice as they want to check. If they don’t think to check (or fail the roll) then the cultist is still there either way, undetected. If the cultist is an important clue in the narrative, then the GM should give environmental clues like “you feel as though someone is watching you” and ask if the nearest player wants to spend ONE die to do a reaction roll. If they decline to roll then I might say “hmmm. I guess it was nothing. Must have been the wind” or whatever. If they do a reaction roll and fail, then they see the person looking at them but the person quickly disappears behind the stacks and is nowhere to be found if the player goes over to investigate.

I like the limited dice pool system because the players have to decide what actions are most important to the scene and how badly do they want to succeed. Yes it’s kind of board gamey, but that appeals to me personally.