OptionalcolorOptionaldataOptional opaque numeric payload for drawings that derive geometry
from sampled data rather than purely from anchors — currently the
regression channel, which stores the close series of its index
span so the least-squares fit round-trips exactly without needing
the candle buffer at render time. Subclasses that don't use it
leave it undefined, so existing snapshots stay byte-compatible.
Serialized form of a drawing — JSON-safe representation for persistence (localStorage, remote API, etc.).
kinddiscriminates the subclass;idis a stable random string assigned on creation.