Clicking "Install Hermes locally" surfaced no error when the bridge was
missing, if the click landed before React drained the passive effect that
reacted to the first bootstrap snapshot. The effect cleared the transient
button state on every change of setupChoice.activeRoot, and the very first
snapshot counts as a change: it moves the root from null to its initial
value. The choice paints as soon as that snapshot commits, so a fast click
produced an error that the effect then cleared before it ever rendered.
The state now records the root it was produced under and is read back only
under that same root, so leaving a phase still discards it but arriving in
one cannot. Deriving it removes the effect rather than adding a guard to it.
Reproduced by observing the DOM with a MutationObserver instead of findBy*,
which only settles on a timer tick — by then the effect has already run and
the window is closed. Reverting the component change fails the new test.
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