Beehiiv redirects non-existent newsletters to /?404=... with HTTP 302.
With follow_redirects=True, the final 200 was misread as "newsletter exists".
Fix: disable redirect following so only a direct HTTP 200 = newsletter real.
Also reset state back to last_sent=13 (real).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>