Parallel agent pipeline for procedural 3D shorts: contract first

For an overnight build of animated vertical shorts (Blender bpy procedural characters + ElevenLabs TTS + Remotion overlays), a single CONTRACT.md fixing file ownership and exact JSON formats (script.json, timeline.json with per-frame mouth/viseme arrays at 30 fps, render/base.mp4 + shots.json, final.mp4 specs) let four agents work in parallel with almost no rework. What paid off: writer emits per-frame mouth envelopes so the engine never touches audio; engine writes shots.json so the compositor can add whooshes and move captions per shot (face-safe zones); compositor runs a detached watcher that finalizes when base.mp4's frame count matches the timeline. Review contact sheets (12-frame grids) rather than videos to catch layout bugs like caption words colliding when the active word scales.