There are several ways to do callback-ish things in I7. Rulebooks, rules, activities, or to-phrases can all be passed as parameters or stored as properties of kinds. But values of kind text that include adaptive text can be meaningfully viewed as callbacks in and of themselves.
An npc_journey has a text called the say_before_moving.
The say_before_moving of journey_lee_walk is "[lee_before_moving]".
To say lee_before_moving: [...]
It sounds to me like you’re clear on how texts that include adaptive text are really functions waiting to be called, i.e., they’re Schrödinger’s Cats existing in a state of quantum wossname until some moment when the wave function collapses and you find out what they really are. I’m not sure, but I think you may be thinking that using to decide what text or not plays a role in whether you’re getting an actual fixed string of characters whose wave function has already collapsed. It doesn’t; that’s a red herring.
It’s normal to be confused by this: it’s confusing and the docs could do a better job of addressing it. It left me confused for longer than I wished, for sure. See my discussion of texts here along with @drpeterbatesuk 's follow-ups.
It’s helpful to know that “text” (text that includes adaptive text) and “indexed text” (ordinary strings) used to be different kinds and they still are, under the hood. You can test which is which with if t is substituted (what used to be called “indexed text”, a plain string) or if t is unsubstituted (what used to be “text” as opposed to “indexed text”, i.e., something much like a reference to a function).
So…
To say foo: say "foo".
To decide what text is bar: decide on "bar".
when play begins:
let t be "plugh"; [ t is substituted ]
now t is bar; [ substituted ]
now t is "[foo]"; [ unsubstituted ]
now t is "[bar]"; [ unsubstituted ]
now t is the substituted form of t; [ substituted ]
[ t would always be substituted after that, no matter what had been on the right-hand side of `substituted form of` ]
So it’s possible for a to decide what text phrase to return a substituted or unsubstituted text. But even if what it returns is a substituted text, as in to decide what text is bar above, one could use "[bar]" instead of bar and then one would have an unsubstituted text. You and I may know that the substituted form of "[bar]" will always be “bar”, but I7 doesn’t “know” that.
I hope that clarifies how you can get what you want when you want it.
(As you’ve described what you want out of npc_journey, it has sounded to me like it would have been a good candidate for a family of rulebooks, but it sounds like a whole different representation isn’t what you’re after.)