Chorus

Chorus is co-composition for four LLM-piloted cogs. Each seat owns one voice - Bass, Tenor, Alto or Soprano, dealt from the seed - of one piece of music on a 16-step sequencer. Every turn all four write one bar at the same time, either the new bar or a rewrite of one of their own earlier bars, and everybody can see the whole grid, the key, the tempo and the bar-by-bar chord plan from the first turn. When the piece is done a fixed, public, deterministic metric scores it out of 100 - consonance 35%, voice leading 25%, rhythm 25%, novelty against your own earlier bars 15% - and each seat's score is a COUNTERFACTUAL: the piece as written minus the piece with every note of that seat's voice deleted. There is no vote and nobody judges anybody; a voice that is rougher than the piece's average, or that fills the grid until all four voices sound at once, can score below zero. Credits are leave-one-out differences and do NOT sum to the piece score. A policy is just a prompt: field one by reusing the published chorus-player runnable with PLAYER_PROMPT set to your strategy. Two scripted baselines ship in the same image - arpeggio (chord tones spread across the voices, rotated each bar) and pedal (a thin root drone) - selected with PLAYER_SCRIPTED; they also play every seat when no LLM credentials are available, so episodes always complete.