In this hypothetical one chance to detect a trap world what happens when wormtongue casts create traps and your searching is poor enough that you cannot see them? You just have to walk on one and hope it isn't a nasty one?

A simple answer would be that any trap created in the player's LOS is visible.

When I was thinking about implementing this in DaJAngband, I was thinking the really tough thing about making monsters affected by traps is how to keep track of whether the trap was set by the PC, by monsters, or already there. Obviously, a monster shouldn't be affected by a trap that it created.
IMHO, I don't think there's much point in having monsters affected by traps if there's no way for the PC to set traps. (Except maybe for that scenario of a frightened monster running onto a teleport trap, but I don't like the idea of monsters using summoning traps. There's already too much summoning in the game, I don't want to give monsters with no summoning spells a way to summon.)

Yep, that's what I'm doing in Fay 1.2, too: traps created by Create Traps are visible.

Brogue uses traps well. The traps are probably as dangerous as the monsters. There's a lot of traps and they are effective since detection is scarce. Monsters can trigger traps which are more often than not (maybe always) area of effect, clouds, explosions, etc. so even it's it a monster that trips it, the player it likely to be affected by it. It quite exciting to have your pet ogre set off a paralysis gas trap that engulfs you and a few enemies and then waiting to see who regains mobility first.

Quickband seems to me to have a good trap system, after playing the latest competition I found traps that shoot bolts at you, somethings that explode on you making death by traps very possible.