dmarc: a report is bounded, kept per domain, and ingested one at a time

Security review of the DMARC report path (Fable, 2026-10-11), which ran
for the first time in 2.0.0. No Critical or High finding. Fixed:

- Medium: a report was bounded only as 8 MiB of XML - some 160 000
  records or one name of megabytes, all of it rows and table cells. At
  most 5 000 records (more is ErrRejected, dropped), text fields cut to
  255 bytes on a character boundary, a record's count capped.
- Medium: the cap of 500 reports was for the whole server, so a stranger
  filing under one domain's address evicted every other domain's
  reports. PruneDMARCReports counts per domain.
- Low: the pipe service ran up to default_process_limit (100) commands
  at once against the panel's database; maxproc is 1.
- Low: the reason logged for a dropped message carried the sender's
  bytes (header line, zip entry name) as they came; cut to 200 bytes and
  reduced to printable ASCII, zip entry names quoted.
- Low: SELFPOST_DATA_DIR / SELFPOST_DB_PATH with whitespace or "$" would
  reach the command through export_environment as another path; refused
  at start when DMARC ingest is on.

Left as they are, told to the owner: the parse-failure count is a
lifetime figure shown under "This week"; a report larger than the
command reads is dropped as unreadable; nested multipart is not searched.

The hub's Retention line follows the design commit before this one.
security.md: the review, and the accepted-risk entry says what a
stranger can and cannot do now. The roadmap no longer calls the review
pending.

  go vet ./cmd/... ./internal/dmarc/ ./internal/store/: ok
  go test ./cmd/... ./internal/dmarc/ ./internal/store/ ./internal/web/...: ok
  make e2e on the test server (with the port-25 scenarios of the next
  commit): ok

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

cmd/panel/dmarc_ingest.go

@@ -50,8 +50,24 @@ func runDMARCIngestMode() error {
 // all of which that line already has. postlog is no use here: pipe(8) starts
 // the command without the group that may write to Postfix's log socket.
 func logRejected(reason error) {
-	text := strings.TrimPrefix(reason.Error(), dmarc.ErrRejected.Error()+": ")
-	fmt.Fprintln(os.Stderr, "dropped: "+text)
+	fmt.Fprintln(os.Stderr, "dropped: "+logSafe(strings.TrimPrefix(reason.Error(), dmarc.ErrRejected.Error()+": ")))
+}
+
+// logSafe makes a reason fit for a log line. Parts of it are the sender's own
+// bytes - a header line, a file name inside an archive, a piece of XML - so it
+// is cut short and anything that is not printable ASCII becomes "?", whatever
+// Postfix would have done with it.
+func logSafe(s string) string {
+	const max = 200
+	if len(s) > max {
+		s = s[:max]
+	}
+	return strings.Map(func(r rune) rune {
+		if r < 0x20 || r > 0x7e {
+			return '?'
+		}
+		return r
+	}, s)
 }
 
 // ingestRecipient is the report address the message was delivered to. Postfix's

cmd/panel/dmarc_ingest_test.go

@@ -18,3 +18,17 @@ func TestIngestRecipient(t *testing.T) {
 		}
 	}
 }
+
+func TestLogSafe(t *testing.T) {
+	got := logSafe("zip entry \"a\nstatus=bounced\tx\" \x1b[31m é")
+	if want := "zip entry \"a?status=bounced?x\" ?[31m ?"; got != want {
+		t.Errorf("logSafe = %q, want %q", got, want)
+	}
+	long := make([]byte, 1000)
+	for i := range long {
+		long[i] = 'a'
+	}
+	if got := logSafe(string(long)); len(got) != 200 {
+		t.Errorf("logSafe kept %d bytes of 1000, want 200", len(got))
+	}
+}