IMAP_EMAIL_SEED / POP3_EMAIL_SEED accept a directory (rglob *.eml +
*.json) or a single .json/.eml. Loaded entries CONCATENATE with the
hardcoded _BAIT_EMAILS — additive to the realism-engine emailgen
output rather than replacing it. JSON dicts require from_addr /
to_addr / subject / body; bare bodies are wrapped into RFC 5322 on
load. compose_fragment reads service_cfg["email_seed"] and bind-mounts
the host path read-only at /var/spool/decnet-emails/seed.