Mirrors the Google sleep suites name for name: the mapper keeps its externalIds
across a re-score that re-classifies and renumbers segments, the sweep stays
bounded to the night's window and never touches the fresh keep-set, a null
window issues no delete at all, and a cleanup failure never fails the sync.
The end-to-end fixture runs one night stored under the old keys through
`syncUserSleep` and pins the ordering the heal depends on — sweep first, then
the rescue re-keying the tombstoned rows in place, no parallel insert — plus a
second pass that writes nothing at all.
Also covers the repair's verdict gates (bounded 365-day window, marker stamped
only on a clean run, watermark untouched, dead token and reauth park returning
without a stamp), the unchanged-value skip including the re-classified segment
it must not swallow, and both Retry-After paths.
