audit 2c: the rest the sources contradict, and the documents

Code and config:
- C-M7: a DMARC report's explicit <pct>0</pct> stays 0; only an absent
  pct takes RFC 7489 § 6.3's default 100 (Pct *int).
- C-D1: docs/development.md now tables the Debian versions the citations
  were read at (postfix 3.7.11-0+deb12u1, opendkim and libopendkim11
  2.11.0~beta2-8+deb12u1, libmilter1.0.1 8.17.1.9-2+deb12u2, libsasl2-2 and
  sasl2-bin 2.1.28+dfsg-10, supervisor 4.2.5-1, logrotate 3.21.0-1 - read off
  the image with dpkg-query, 2026-10-15); the e2e stand's new
  checkCitedPackageVersions fails when the image it built differs.
- C-E2: the e2e zone's SOA serial only grows (CoreDNS v1.14.6's file
  plugin reloads on a grown serial, not on mtime); Corefile comment says
  so; TestZoneSerialGrows.
- C-K8, C-K9: the e2e compose and stage comments say how
  --project-directory and .env resolve.
- D-arch:154: postfix-config.sh's "Postfix insists" comment says what
  TLS_README advises and that smtpd reads the key as root.
- B-G7: inflight.go's reservationTTL comment: a dropped client does give
  ABORT (smtpd_proto() -> mail_reset() -> milter_abort()); the TTL is for
  smtpd dying or the milter connection breaking.
- D-guide:301: the nginx fragment's first-certificate command now reaches
  certbot (--entrypoint certbot, --standalone, port 80 free), and the
  renewal loop passes --webroot -w /var/www/certbot - a standalone
  certificate would otherwise renew standalone while nginx holds port 80
  (certbot docs, "Renewing certificates": the issuing plugin is used
  "unless you specify other plugins or options", and options of a
  successful renewal are saved). The register's proposal missed that.

Documents: every D-arch, D-guide and D-sec claim the register's Answers E
found false or partly true, rewritten - by three Sonnet agents, one per
document, then reviewed: two proposals were obsolete after this stage's
fixes and not used (a bounce's From: line - extract_from = "smtp" now;
"Origin: null" - Referrer-Policy is same-origin now); a stand
observation the agent had dated from a commit is now tied to the e2e test
that checks it; the SQLite writers paragraph describes _txlock=immediate;
the log tailer's rotation paragraph describes the minute's grace; the
guide's nginx steps were put in working order (links and modes before
`up`, no reconfigure step). "Deferred" is kept for Postfix's queue in the
guide too. guide.md's CRLF from the agent normalised.

Stand (2026-10-15, make e2e, exit 0, the version gate and zone serial
test included); go vet and go test ./... pass on the server (24 packages).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/dmarc/parse.go

@@ -60,7 +60,7 @@ type feedbackXML struct {
 		Domain string `xml:"domain"`
 		P      string `xml:"p"`
 		SP     string `xml:"sp"`
-		Pct    int    `xml:"pct"`
+		Pct    *int   `xml:"pct"`
 		ADKIM  string `xml:"adkim"`
 		ASPF   string `xml:"aspf"`
 	} `xml:"policy_published"`
@@ -132,12 +132,15 @@ func ParseAggregate(raw []byte) (ParsedReport, error) {
 		Domain:       strings.ToLower(field(doc.Policy.Domain)),
 		PolicyP:      field(doc.Policy.P),
 		PolicySP:     field(doc.Policy.SP),
-		PolicyPct:    doc.Policy.Pct,
 		PolicyADKIM:  field(doc.Policy.ADKIM),
 		PolicyASPF:   field(doc.Policy.ASPF),
 	}
-	if out.PolicyPct == 0 {
-		out.PolicyPct = 100
+	// RFC 7489 § 6.3: pct is "between 0 and 100, inclusive", 100 when absent.
+	// An explicit 0 is a policy applied to no message, and stays 0; only a
+	// report without the element gets the default (assumptions C-M7).
+	out.PolicyPct = 100
+	if doc.Policy.Pct != nil {
+		out.PolicyPct = *doc.Policy.Pct
 	}
 	for _, rec := range doc.Records {
 		row := ParsedRecord{