4.9.1 - tvOS build fix
Hotfix on top of 4.9.0: the segment-retention free-space clamp queried volumeAvailableCapacityForImportantUsage, which does not exist on tvOS and broke the tvOS build. tvOS now uses the plain volumeAvailableCapacity key; iOS and macOS keep the important-usage variant. No behavior change otherwise; see the 4.9.0 release notes for the feature set.