stems-to-mixdown

Sum a directory of multitrack audio stems into stereo mixdowns (acapella, instrumental, custom groupings) at the highest quality the source material honestly supports. Six-pass pipeline (identify → optional Pro Tools track-name borrow → analyze → plan → mix → verify) with full provenance: SHA-anchored idempotency, sidecar logs per output, declared pan law, ITU-R BS.1770 true-peak headroom, dither when reducing depth, and refusal-by-default for upsampling, normalization, and writing into the source folder. Optional master-reference pipeline (Cmd 19) produces a three-synced-versions reference-bundle and runs a recombine-null + inverse-stems-null verification battery against the released master. Eighteen commandments, all cited by error messages and plan rationale.