The most recent playtest verified my suspicion that the rules I needed were not “crunchy” but “soft”.
I spent some time working out contexts in which the GM might want to say “that might not be so easy” and present some opposition, coupled with principles for the GM to use to push forward and provoke the PCs into trying things that might turn out to not be so easy. All very “soft” in that it’s all rules about what you say and what sort of cues might trigger saying such things. Almost no reference to economies and points and cards and such. Rules like this are obviously very important, but are something I have much less practice thinking about or creating.
The other thing this did was it allowed for the breathing room that I mentioned a few posts ago. It became much easier to see which scenes should include opposition (and thus expenditure of tokens and cards) and which shouldn’t, instead setting up the next moment of high drama or allowing characters to show off how they recover.
So, to continue the anatomical metaphor, I think I’ve found the lungs of this system: empty spaces, made of flesh not bones, with some conscious control. They give the heart something to pump around.