I finally reproduced this issue myself on a fresh install on Windows.
We needed explicit file closing here as going out of scope doesn't immediately finalize (and close) a File object. That may not happen until garbage collection and thus prevent subsequent re-opens of the same files, so always close() your files.
init-fidonet.js calls install-binkit.js which uses cfglib.js, so that was
a source of these errors too.
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