motion-doctrine

Match the exit and entry vectors across every cut: same axis, same direction, and matched speed, cutting mid-motion on both sides. Write one ledger.json row per seam and verify it numerically with the seam-gate script before shipping.

Run seam-gate.mjs verify with your ledger.json and project directory. It launches headless Chrome over CDP, samples element positions around each cut, and fails the build if exits settle early, entries start from rest, or both sides overlap.

On the Z axis, direction is the sign of scale change: growing means push forward, shrinking means pull back. A receding exit answered by a grow-from-small entry is a mirrored vector and fails the gate's z-sign-scan check.

Zero-overlap fails when both scenes are visible in the same frame, which reads as a dissolve. The usual cause is a clip whose data-start precedes its entry tween; set initial autoAlpha to 0 and data-start exactly at the cut time.

No npm dependencies are required. The scripts use only node 22 or later built-ins plus a local Chrome or chrome-headless-shell binary, which is auto-discovered from the puppeteer cache or system installation.

Hand-author only Tier-A morphs and match-cuts, where a shared carrier element crosses the cut. The stamp script writes visibility sets for these rows, and the gate checks carrier rect continuity instead of full vector motion.