BUILTIN_SHAPE_MIGRATION_SEQUENCE_PREFIX

The prefix for migrations on shapes **this library ships**.

Deliberately NOT com.tldraw.shape. A .tldr written by the reference implementation carries its own sequence for every built-in — geo was at version 12 when this was written — and a schema that registers the same sequence id is claiming to be that migration line. Registering ours at version 1 made every real file fail to load with "data comes from a newer version"; leaving the id unclaimed makes the file's sequence unknown, which is ignored with a warning and the props load as written.

An app's own custom shape types keep SHAPE_MIGRATION_SEQUENCE_PREFIX: nothing else claims those names, and a document records its progress under them.