Belt-and-suspenders for the edge you flagged: a domain already in a warmup list
could flip its MX to Google Workspace between weekly refreshes, after which it
would hard-bounce from the cold IP. The import-time guard only catches NEW adds.
- prune_holdouts(): enumerates each warmup list's subscribers, matches them
against the FRESH master CSV (re-classified weekly), and removes any whose
domain is now Google-hosted. DELIVERABILITY-ONLY -- it never evicts for
audience reasons (an overdue provider drifting out of the 1-90 day window was
a valid target when warmed; re-litigating that just wastes warmup progress).
- --prune (run alongside warming) and --prune-only (prune then exit).
- Wired into the weekly refresh cron as a --prune-only chained step, so MX is
re-checked and holdouts removed every Monday before the weekday sends.
Verified end-to-end: with no Google domains in lists it's a 0-op; injecting a
simulated Google-flipped domain into the master, the prune correctly detects and
(in a real run) would remove it from every list it's on.
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