Frontend unit tests run in a plain node environment, so nothing that
renders can be covered and no hook can be tested under real React. The
workaround that forces is already in the tree: the use-global-shortcuts
test mocks out react itself, so its useEffect never re-runs on a
dependency change and never goes through React's commit/cleanup
ordering -- it pins the stub rather than the hook.
Split the suite into two rstest projects: *.test.ts(x) keeps running on
node, *.dom.test.ts(x) runs on happy-dom. A global DOM environment was
measured first and rejected -- it takes the same 743 tests from 3.3s to
9.5s -- and rstest has no per-file environment docblock, so projects is
the only way to charge that cost to the tests that need it.
useIsMobile is the first consumer: it had no tests and cannot have any
without a document, since it reads window.matchMedia.
