Mock send_email and call each handler directly. Covers recipient,
subject content, HTML design elements (wordmark, preheader, heat
badges), from_addr, skip-on-missing-data guards, and email_sent_at
timestamp updates.
Also fixes IndexError in handle_send_welcome when payload has no name
("".split()[0] → safe fallback).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
