fix

internal/model/record.go

@@ -55,7 +55,9 @@ func normalizeName(name string) string {
 // normalizeValue canonicalizes a single RR value for comparison.
 func normalizeValue(t RecordType, content string) string {
 	if t == TXT {
-		return content // byte-exact — case and whitespace are significant (DKIM/SPF/DMARC)
+		// byte-exact — case and whitespace are significant (DKIM/SPF/DMARC);
+		// only the presentation quoting/chunking is stripped.
+		return TXTPayload(content)
 	}
 	c := strings.Join(strings.Fields(content), " ") // collapse whitespace
 	switch t {
@@ -95,3 +97,47 @@ func (r Record) Equal(o Record) bool {
 	}
 	return slices.Equal(r.NormalizedValues(), o.NormalizedValues())
 }
+
+// TXTPayload returns the logical content of a TXT value. A value written as
+// one or more quoted strings ("a" "b") is the concatenation of their
+// contents; an unquoted value is returned as is. This makes a template value
+// without quotes comparable with the quoted form providers store.
+func TXTPayload(v string) string {
+	t := strings.TrimSpace(v)
+	if !strings.HasPrefix(t, `"`) {
+		return v
+	}
+	var b strings.Builder
+	inQ := false
+	for i := 0; i < len(t); i++ {
+		c := t[i]
+		switch {
+		case inQ && c == '\\' && i+1 < len(t):
+			i++
+			b.WriteByte(t[i])
+		case c == '"':
+			inQ = !inQ
+		case inQ:
+			b.WriteByte(c)
+		}
+	}
+	return b.String()
+}
+
+// QuoteTXT renders a TXT value in the quoted form providers require: payload
+// split into <=255-byte strings, each quoted. Already-quoted values pass
+// through unchanged.
+func QuoteTXT(v string) string {
+	if strings.HasPrefix(strings.TrimSpace(v), `"`) {
+		return v
+	}
+	const max = 255
+	esc := strings.NewReplacer(`\`, `\\`, `"`, `\"`)
+	var parts []string
+	for len(v) > max {
+		parts = append(parts, `"`+esc.Replace(v[:max])+`"`)
+		v = v[max:]
+	}
+	parts = append(parts, `"`+esc.Replace(v)+`"`)
+	return strings.Join(parts, " ")
+}

internal/model/txt_test.go

@@ -0,0 +1,30 @@
+package model
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestQuoteTXTAndPayloadRoundTrip(t *testing.T) {
+	long := "v=DKIM1; p=" + strings.Repeat("A", 400)
+	for _, v := range []string{"v=spf1 ~all", long, `a"b\c`} {
+		q := QuoteTXT(v)
+		if !strings.HasPrefix(q, `"`) {
+			t.Fatalf("not quoted: %q", q)
+		}
+		if got := TXTPayload(q); got != v {
+			t.Fatalf("roundtrip: got %q want %q", got, v)
+		}
+		if TXTPayload(v) != v && !strings.HasPrefix(v, `"`) {
+			t.Fatalf("unquoted payload changed")
+		}
+	}
+	if QuoteTXT(`"x"`) != `"x"` {
+		t.Fatal("quoted must pass through")
+	}
+	a := Record{Type: TXT, Values: []string{"v=DKIM1; k=rsa"}}
+	b := Record{Type: TXT, Values: []string{`"v=DKIM1; k=rsa"`}}
+	if !a.Equal(b) {
+		t.Fatal("quoted and unquoted must compare equal")
+	}
+}