motion-doctrine

Match the exit and entry vectors across every cut: same axis, same direction, and matched speed, cutting mid-motion on both sides. Plan all seams in a vector ledger before authoring, then verify them numerically with the seam gate script.

Run node seam-gate.mjs verify --ledger ledger.json --project <dir>. It spawns a preview server, drives headless Chrome over CDP, samples element positions around each cut, and exits 0 only if direction, speed, overlap, and carrier checks pass.

On the Z axis, direction is the sign of scale change: growing means push, shrinking means pull. A receding exit answered by a grow-from-small entry is a mirrored vector and fails the gate; the incoming scene's own entrances are also scanned for sign-fighting.

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, it has zero npm dependencies. It requires Node.js 22 or later and a local Chrome or chrome-headless-shell, which it finds automatically in the puppeteer cache or via the CHROME_PATH environment variable.

Hand-author only Tier-A morphs and match-cuts, where a carrier element hands off across the cut. These rows get visibility sets from the stamper, and the gate checks only carrier continuity and overlap for them.