The Steel rules are not in Hub and Spokes.
But p 72 is there. There is no social agreement for the resolution of conflict in this game. Yet that is what you repeatedly advocate - that the player asks for their to be a cup, so that they can pursue their Belief, and you think the GM should just say "yes".
As for Steel, I've already told you that cold-blooded murder is a trigger for a Steel test. Here's a post that says a bit more about it:
Of course you don't have to believe me.
And of course you ignore the bulk of my post.
OK, sure. players and GMs are not allowed to simply decide something exists. The player must always roll for it, except when the GM says yes, which they can't do except when they can.
This may be the rule in BW, but again, I find this to be a bad rule.
So let's turn to page 72.
Or this leads to a game feeling boring, antagonistic, pointless, and random, and as a result, unfun.
I have never felt heroic or grandiose for passing a regular check. What makes my character feel heroic or grandiose when it involves dice is if the events that caused my roll are heroic or grandiose. If a "spot the thing" check needs to feel heroic to me, then it needs to be something like this:
(Do you see the kitty? And by kitty, I mean jaguar. Photo was taken by 16-year old Bella Lack)
and not like this medieval woodcut of a sick room.
(look! vessels!)
Over on r/rpghorror stories, I sometimes seeing stories of games where the player will say something like "I'm checking the room for traps" and then get caught in a trap anyway--not because they didn't roll well enough but because the GM said something like "you said you were checking the room; you didn't say you were checking the
ceiling." That's the vibe I'm getting from this game.