Some image_record rows store tagger_predictions as a JSON scalar/null rather
than an object; json_each throws 'cannot deconstruct a scalar' on those,
rolling back the whole migration. Filter to json_typeof = 'object' in a
MATERIALIZED CTE so the guard runs before json_each ever evaluates a scalar.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>