Type Alias WhiteboardWidgetSubmitDropReason

WhiteboardWidgetSubmitDropReason:
    | "not-submit"
    | "unknown-source"
    | "oversize"
    | "unserializable"

Why an incoming 'message' event was NOT surfaced as a widget submission.

"not-submit"
Not a bridge message at all (no marker) — other postMessage traffic, ignore silently.
"unknown-source"
Marker present but event.source is not a tracked widget iframe — spoof/stale, drop.
"oversize"
Payload serialized beyond the cap — warn + drop.
"unserializable"
Payload could not be JSON-serialized (e.g. undefined / function) — drop.