SelectionMaskCache

The selection mask, computed again only when what it depends on changes (construct-stress-hardening `U1`).

In the namespace construct::selection. Declared in src/libs/libconstruct/construct/selection/HighlightCaches.hpp.

Detailed description

The mask depends on the selection and on the SDF node map, and the node map changes exactly when SDFLayer::nodeStructureGeneration() moves. The inline viewport computed it on every rendered frame, which walked the selected subtrees per frame; the worker viewport had keyed it on these two things since 2026-08-24. Both use this class now.