A confirmed-404 workout must stop being retried forever, but
workout_raw_json should never be fabricated -- it stays null exactly
as it does for "not yet fetched." workout_not_found_at is the
separate marker ActivitiesMissingWorkout/CountActivitiesMissingWorkout
now check for, mirroring the existing pattern of the other _fetched_at
columns. UpsertActivity's ON CONFLICT clause already never touches
these columns, so the marker persists across every later re-sync.
Christophe Vila
7d371219b7