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>

test/e2e/dns_zone.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -38,12 +39,16 @@ type txtRecord struct {
 
 // writeZone (re)writes the whole authoritative db.zone for e2e.test: the fixed
 // records CoreDNS/sink need to be reachable, plus whatever TXT records the
-// test has published so far. CoreDNS's `reload 2s` (see dns/Corefile) picks up
-// the new mtime with no signal needed.
+// test has published so far. The file plugin's `reload 1s` (see dns/Corefile)
+// reloads the zone when its SOA serial has grown - not on a new mtime:
+// CoreDNS v1.14.6, plugin/file/reload.go, Reload() re-parses with the current
+// serial and file.go, Parse(), refuses a zone whose serial did not change
+// (coredns.io/plugins/file, "reload"; assumptions C-E2). So the serial only
+// ever grows, by one at least, even for two writes within a second.
 func writeZone(stageDir string, extra []txtRecord) error {
 	var b strings.Builder
 	fmt.Fprintf(&b, "$ORIGIN e2e.test.\n$TTL 300\n")
-	fmt.Fprintf(&b, "@       IN SOA  ns.e2e.test. admin.e2e.test. ( %d 3600 900 604800 300 )\n", time.Now().Unix())
+	fmt.Fprintf(&b, "@       IN SOA  ns.e2e.test. admin.e2e.test. ( %d 3600 900 604800 300 )\n", nextZoneSerial())
 	fmt.Fprintf(&b, "@       IN NS   ns.e2e.test.\n")
 	fmt.Fprintf(&b, "ns      IN A    10.77.0.10\n")
 	// The sink-MX: Postfix's outbound delivery for the recipient domain used by
@@ -58,6 +63,20 @@ func writeZone(stageDir string, extra []txtRecord) error {
 	return os.WriteFile(filepath.Join(stageDir, "dns-stage", "db.zone"), []byte(b.String()), 0o644)
 }
 
+var zoneSerial struct {
+	sync.Mutex
+	last int64
+}
+
+// nextZoneSerial is the time in seconds, or one more than the last serial
+// when that is not later.
+func nextZoneSerial() int64 {
+	zoneSerial.Lock()
+	defer zoneSerial.Unlock()
+	zoneSerial.last = max(zoneSerial.last+1, time.Now().Unix())
+	return zoneSerial.last
+}
+
 // chunkTXT splits a TXT value into <255-byte quoted strings (the DNS
 // <character-string> limit, RFC 1035 § 3.3), which a DKIM verifier
 // concatenates back into one value (RFC 6376 § 3.6.2.2).