-- Backfill des miniatures YouTube manquantes (imports Takeout sans vignette).
-- Les miniatures YouTube sont déterministes : i.ytimg.com/vi/<id>/hqdefault.jpg
UPDATE watch_history
SET thumbnail = 'https://i.ytimg.com/vi/' || video_id || '/hqdefault.jpg'
WHERE provider = 'youtube'
  AND (thumbnail IS NULL OR thumbnail = '')
  AND length(video_id) = 11;