setupOldButton() polled the DOM every 4s forever after the menu editor
first opened, with no way to ever stop - the interval id was not even
kept in a variable. It now returns whether the button was found, the
interval only starts when the first attempt fails, and clears itself
on the first successful attempt (also wired into the existing
disconnect() cleanup alongside the other timers).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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