The planet is the boss.

Planets are interpreted as “people.” Signs and Nakshatras are interpreted as “places.” People do things in places, using the resources of the place. Sure, the environment and resources affect what the person can do and how they do it (this is what planetary “dignity” is all about, for example), but the active agent, the “boss,” is always the planet, and the passive agent is always the sign / nakshatra.

Q: But from Taittiriya Brahmana it seems nakshatras have their own agenda. Every sūtra on every nakṣatra describes them “needing X to make Y” (avastat / parastat)?

When a planet is in a nakshatra, it will try to supply the X to produce the Y. It is not that the nakshatra has become the boss, but the environment and its resources always affects what a person can do in it. You may want to get drunk and dance, but if you are in the library at your school, the environment and resources will not permit that activity very well. Conversely, you may want to study but if you are at the bar with friends at midnight…

“The library needs books to produce knowledge.” It doesn’t mean the library is a person. It means that when people use the library, the result will be knowledge for them, if they access and utilize the books. “The party needs snacks to produce fun.” Again, it doesn’t mean the party is a person walking around looking for snacks because it wants to have fun. It means when the people come to the party, they will have fun, as long as they can access some good snacks, etc.