ingest() puts metadata on the interaction, not the thread, and listThreads filters
THREAD metadata — so MailService now tags the thread directly after deposit
(source=crm-mail). Lets the CRM list mail threads apart from Messenger chat
(source=crm-messenger). 7 tests. NOTE: requires an IIOS redeploy.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>