Migration 0420 looked for an RMSSD twin by externalId only. A Fitbit or
Google Health SDNN row with no externalId, or another one, on the same
night as an RMSSD row would have broken the measured-at unique key and
aborted the block at boot. The twin check now matches either identity,
a row left behind by a live twin is tombstoned, and an RMSSD tombstone
that would make a live row look twinned is removed so the row moves.
The backup restore applies the same rule and no longer counts a
tombstone as a twin.
Fitbit's `dailyRmssd` and Google Health's daily HRV average are both
RMSSD, but the mappers wrote them into HEART_RATE_VARIABILITY, the SDNN
series. The `hrv` ladder ranks both above Apple Health, so an account
with an Apple Watch and a Fitbit had a series that switched estimator
from day to day. The mappers now write HRV_RMSSD, and the `hrvRmssd`
ladder carries both sources where they sat on the SDNN one.
Migration 0420 moves the rows already written (tombstones included,
with a sync-version bump so the change reaches the phone), drops their
SDNN rollup buckets and the RMSSD buckets of every account whose rows
moved, so the boot-time rollup discovery folds those accounts again,
and deletes the SDNN personal records those rows had set. One DO
block, so the move and its cleanup land together.
Marc-André Bombeck