When a Suspense boundary suspends during initial mount, the primary
children's fibers are discarded because there is no current tree to
preserve them. If the suspended promise never resolves, the only way to
retry is something external like a context change. However, lazy context
propagation could not find the consumer fibers — they no longer exist in
the tree — so the Suspense boundary was never marked for retry and
remained stuck in fallback state indefinitely.
The fix teaches context propagation to conservatively mark suspended
Suspense boundaries for retry when a parent context changes, even when
the consumer fibers can't be found. This matches the existing
conservative approach used for dehydrated (SSR) Suspense boundaries.
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