Add Drift TypeConverters for the two structured JSON columns in the Threads table (participantsJson → List<EmailAddress>, emailIdsJson → List<String>). The DB layer now owns serialisation for these fields; _threadRowToModel no longer calls jsonDecode by hand. Also extract _parseAddresses() helper to deduplicate the two identical local functions that decoded Emails address columns. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>