After iOS reinstall/restore the app container UUID rotates, which left both
the persisted source.url and the security-scoped bookmark pointing at a
no-longer-current path. Files derived a stale absolute path that got appended
onto the resolved bookmark, producing doubled URLs that MPV could not load.
- Resolve the base URL by picking whichever of the bookmark or source.url
actually exists on disk.
- Compute MediaFile relative paths against the resolved root so they survive
later container changes.
- Hold the security-scoped resource access for the source's lifetime via a
shared resolver, so MPV can open files long after the directory enumeration
that resolved the bookmark has returned.
- Normalize legacy absolute paths embedded in old recents/history video IDs
so they re-resolve under the current container.
