The unmount cleanup deferred its store.reset() to a rAF so navigating
pages had a chance to overwrite the store first. The deferred reset
checked whether the store still held this hook's snapshot \u2014 if yes,
reset.
But Suspense (and React StrictMode dev double-invoke) trigger a
cleanup-then-resetup cycle on the same hook instance: the cleanup
fires, schedules the rAF, then the setup re-runs but doesn't write
a new snapshot (shallowEqualOptions sees identical options and
skips). When the rAF fires, the store still has the original
snapshot, so the check passes and the store is wrongly reset \u2014
silently dropping the page's layout options (noMaxWidth,
wrapperClassName, etc.) mid-life.
The symptom: campaign pages and other noMaxWidth pages narrowed to
the default max-w-3xl cap a few seconds after opening, whenever
something downstream triggered a Suspense boundary to re-resolve.
Fix: a per-instance 'unmounting' ref. Cleanup flips it to true,
setup flips it back to false. The rAF bails if the hook re-mounted
in between, so only genuine unmounts trigger the reset.
Regression-of: 2bce20ba
Alex Gleason
dfeeb81ab8