The whole container is unreadable — not this one key. Rethrown by
MultiLevelCachingStore.get so the loader surfaces cause, because
reporting it as a miss would render an empty scene and swallow the
diagnosis a message like RangeUnsupportedError exists to deliver.
Structured failure modes from MultiLevelCachingStore.getResult. Distinguishing them lets callers (prefetcher, retry policies, debug overlays) act on the underlying cause instead of treating every absence the same way.