coversViewport property
true when the node's bounds cover at least kSubtreeTextOmitCoverage
of the viewport at capture time (page root, full-height scroll view).
Such a node's subtree_text would be the whole screen's text, which the
backend can never use as a "tightest container" or a distinguishing
owner label, so toWire leaves it out. In-memory subtreeText is
untouched — the on-device explorer still sees it.
Implementation
final bool coversViewport;