Review follow-up, comments and one type annotation. No behaviour change.
The unmount effect now clears pending timers, but its leading comment is
still entirely about the focus bus, so the cleanup reads as unrelated code
that happens to be in the same block. Say why it lives there: both concerns
are "this composer is going away", they unmount together by definition, and
a sibling unmount-only effect would only be a second place to forget.
In the regression test, the clearTimeout mock declared id as number. Nothing
that reaches it is a number: jsdom under node returns a Timeout object, which
is why the scheduled and cleared arrays are unknown[] and compared by
identity. The annotation documented a shape the test never sees, so it is now
unknown with the cast moved to the one call that genuinely wants a number.
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