Libretto Framework Adds Editable Structure to LLM Music Generation

Libretto wraps symbolic music generation in an LLM-native grammar with explicit onset slots, voices, and bar-level organization, then evaluates output in a corpus-calibrated statistical space covering rhythm, harmony, melody, and form. The framework supports gap filling, reference-guided generation, gradual morphing, and iterative self-revision, turning token sequences into inspectable, editable musical objects.