stem-0-v4-20k — LISTENING CHECKPOINT ONLY

v0.4 r2 decoder at step 20,000. Not a release candidate: this run's training manifest included the 40 validation tracks (builder defect, found 2026-08-21), so its validation numbers are not held-out measurements. Kept for A/B listening against earlier checkpoints. The clean run is v0.4 r3 (manifest 1b6778e6759da159).