The EmailLifter (R0041–R0048) keys on header-derived signals that the
v0 _summarize_message did not extract. Add cheap Layer 2 projections
inside the existing single-pass parse:
* return_path / x_mailer — direct header reads, decoded RFC 2047
* dkim_signed / spf_pass — booleans derived from any
Authentication-Results header (multiple lines tolerated; positive
verdict on any line wins)
* urls — http(s) URLs lifted from text/* body parts via a tight
regex, deduplicated first-seen-wins, capped at 64 in the wire
payload to bound the syslog SD value
Heavyweight extraction (body simhash, office-macro detection,
HTML-smuggling, password-protected archives, mal-hash-match,
body_text projection) stays deferred per the EmailLifter heavyweight
DEBT entry — those rules need privacy / extractor decisions before
they ship.