diff --git a/cloud/tests/HmacTest.php b/cloud/tests/HmacTest.php
index 74af0ba..89d3296 100644
--- a/cloud/tests/HmacTest.php
+++ b/cloud/tests/HmacTest.php
@@ -22,4 +22,17 @@ final class HmacTest extends TestCase
         $this->assertFalse(Hmac::verify('secret', 'n1', '1000.0', 'body-TAMPERED', $sig));
         $this->assertFalse(Hmac::verify('wrong', 'n1', '1000.0', 'body', $sig));
     }
+
+    public function testMatchesGoldenVectorsFromPythonEdgeSigner(): void
+    {
+        // Golden hex produced by running P1-A edge/alert.py::sign — proves cross-language byte-for-byte interop.
+        $this->assertSame(
+            'a151bb402f070c3678056776b1bcc5638bd150dec1e516aaa07cac1a089f63b9',
+            Hmac::sign('secret', 'n1', '1000.0', '{"a":1}')
+        );
+        $this->assertSame(
+            '71865248fe94517dc0305a5c233e2b6c97db95fc9e38815e7c20580d2aa784c9',
+            Hmac::sign('sekret', 'abc123', '1700000000.5', '{"device_id":"pi-1","event_type":"fall"}')
+        );
+    }
 }