fix(xml): preserve UTF-8 declaration in signed DPS output

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

src/Xml/DpsSigner.php

@@ -271,6 +271,12 @@ private function signXml(string $xml, string $privateKeyPem, string $certificate
         $keyInfo->appendChild($x509Data);
         $sig->appendChild($keyInfo);
 
-        return $doc->saveXML() ?: $xml;
+        $serializedDocument = $doc->saveXML($doc->documentElement);
+
+        if ($serializedDocument === false || $serializedDocument === '') {
+            return $xml;
+        }
+
+        return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" . $serializedDocument;
     }
 }

tests/Unit/Xml/DpsSignerTest.php

@@ -122,6 +122,13 @@ public function testSignedXmlIsStillValidXml(): void
         self::assertTrue($doc->loadXML($signed), 'Signed output must be valid XML');
     }
 
+    public function testSignedXmlIncludesExplicitUtf8EncodingDeclaration(): void
+    {
+        $signed = $this->signer->sign($this->testXml, $this->testCnpj);
+
+        self::assertStringStartsWith('<?xml version="1.0" encoding="UTF-8"?>', $signed);
+    }
+
     public function testSignatureElementIsAppendedToDpsRoot(): void
     {
         $signed = $this->signer->sign($this->testXml, $this->testCnpj);