Fuchsia assumes there is a single accessibility root node with ID 0. In a multi-window world, there may be multiple root nodes each with their own unique ID. Thus, Fuchsia must not rely on the root node having ID 0.

See: https://github.com/search?q=repo%3Aflutter%2Fengine+kRootNodeId+path%3A%2F%5Eshell%5C%2Fplatform%5C%2Ffuchsia%5C%2F%2F&type=code