Copilot review round 3.
"stops listening on unmount" asserted that the rendered value stopped
changing after unmount, which proves nothing: React drops a store
notification for an unmounted component whether or not the listener is
still attached, so the test passed with the leak it existed to catch.
Spy the store's add/removeEventListener and assert the exact function
attached is the one detached. Verified it discriminates by deleting the
cleanup, watching this test fail, and restoring.
Signed-off-by: cliffhall <cliff@futurescale.com>
b088b94019