WhatsApp Coexistence echo messages from the native WhatsApp app deliver
Brazilian numbers without the mobile 9th digit. The contact-resolution
layer only deduplicated at the contact_inbox source_id level, so when no
matching contact_inbox existed it fell back to an exact phone_number match
using the un-normalized number, missing the existing contact stored with
the 9th digit and creating a duplicate.
Normalize the phone number used for contact lookup/creation via the
existing Brazil/Argentina normalizers so both formats resolve to the same
contact. Non-affected countries are returned unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
