Extract getVisibleNodeIds/filterVisibleEdges from CanvasContainer into
src/utils/collapseFilter.ts. Replace inline O(n^2) BFS (nested array
.find per node) with O(n) traversal backed by parentId->children and
id->node Maps, and wrap consumer calls in useMemo so visibility is
recomputed only when nodes/edges change rather than on every render.
Add 12 unit tests covering the filter logic that the original PR left
untested: single-level collapse, multi-level subtree hiding via
collapsed ancestor, sibling isolation when an inner zone is collapsed,
empty zones, missing custom_colors, insertion-order independence, and
edge filtering for hidden source/target.
Pouzor
517486ff79