A conductor does not play.
They read a score, bind what it leaves open, cue the entries, and listen to what comes back. That is exactly the position a tool like this is in: it emits, the systems execute, and the only honest thing it can do about the result is listen to it.
So the metaphor is dropped and the thing itself is used. Below is a score of real work. Four parts, four executor spaces, one stage sequence entered at offsets — a fan-out is a canon. Press perform: each note sounds when its task actually completes, so a slow player drags behind the beat and you hear it drag.
the desks cue marks are the plan · the tick is when it really finished · ○ silences a desk
the podium what the score leaves open
Tempo is the dispatch rate; desks are how many players may sound at once — the slot count, which is why concurrency is not configured but simply is how many rows came back and how many desks were free. Raise the load and the players genuinely take longer, so parts begin to drag. Nothing here is a simulation of load: it is more digesting, more rows, more bytes.
what a conductor listens for three things, and each is a real property of the run
A part behind its cue by more than about 25ms — roughly where the ear stops hearing two things as one. It is also flattened, because that is what a dragging player sounds like.
What is sounding together and how rough, by Euler's gradus suavitatis (1739): unison 1, fifth 4, tritone 14. A number, and it agrees with every ear.
A cue that produced nothing. The failure you notice by its absence — the hardest kind to see in a log and the easiest to hear. Silence a desk and try it.