The thinking should be allowed to wander.
The building should not.
That is the simplest version of the playhead idea.
When I am thinking through a system, one idea in the current slice might connect to something five steps ahead. Or something from years ago. Or a future version that is not ready to build yet.
That wandering is useful.
It is how the pattern gets richer.
But if the builders follow every live thought, the system starts producing scattered partial work.
So there needs to be a layer that protects the difference between exploration and execution.
I have been calling that layer Traffic Control.
Traffic Control is the playhead.
It decides what is close enough, clear enough, and useful enough to become real next.
The cockpit can move around the whole timeline. It can explore future ideas, revisit old decisions, chase a weird connection, or reshape something that is not ready yet.
The builders stay near the playhead.
They do the next coherent thing, return proof, wait for review, and then pick up the next thing the system has made ready.
That is the difference between having agents and having an operating system.
Agents can do tasks.
The playhead decides which task should exist now.