diff --git a/archive/v1/tests/unit/test_esp32_binary_parser.py b/archive/v1/tests/unit/test_esp32_binary_parser.py
index f5a34d63..5a5280e9 100644
--- a/archive/v1/tests/unit/test_esp32_binary_parser.py
+++ b/archive/v1/tests/unit/test_esp32_binary_parser.py
@@ -364,3 +364,35 @@ class TestSyncPacketParser:
         assert csi_magic == ESP32BinaryParser.MAGIC
         assert sync_magic == SyncPacketParser.MAGIC
         assert csi_magic != sync_magic
+
+    def test_canonical_wire_bytes_match_rust_decoder(self):
+        """ADR-110 iter 21 — cross-language wire-format conformance gate.
+
+        These exact bytes also appear pinned in the Rust hardware crate's
+        `canonical_wire_bytes_match_python_decoder` test (same field
+        values, encoded by Rust's `SyncPacket::to_bytes`). If Python's
+        hardcoded hex stops matching what Rust produces from the equivalent
+        SyncPacket struct, ONE of the decoders has drifted from the wire.
+
+        Canonical packet: COM9 sync-pkt #1 from §A0.12 live capture.
+        """
+        canonical = bytes.fromhex(
+            "10a111c509010600"   # magic LE + node=9 + ver=1 + flags=0x06 + reserved
+            "f26db70100000000"   # local_us = 28_798_450 (LE u64)
+            "c5aca50100000000"   # epoch_us = 27_634_885 (LE u64)
+            "1400000000000000"   # sequence = 20 (LE u32) + 4 reserved bytes
+        )
+        assert len(canonical) == SyncPacketParser.SIZE == 32
+
+        pkt = SyncPacketParser.parse(canonical)
+        assert pkt.node_id == 9
+        assert pkt.proto_ver == 1
+        assert pkt.flags_raw == 0x06
+        assert pkt.is_leader is False
+        assert pkt.is_valid is True
+        assert pkt.smoothed_used is True
+        assert pkt.local_us == 28_798_450
+        assert pkt.epoch_us == 27_634_885
+        assert pkt.sequence == 20
+        # Recovered offset matches §A0.10's measured 1.16-second boot delta.
+        assert pkt.local_us - pkt.epoch_us == 1_163_565
diff --git a/v2/crates/wifi-densepose-hardware/src/sync_packet.rs b/v2/crates/wifi-densepose-hardware/src/sync_packet.rs
index 55540185..364e7cf1 100644
--- a/v2/crates/wifi-densepose-hardware/src/sync_packet.rs
+++ b/v2/crates/wifi-densepose-hardware/src/sync_packet.rs
@@ -425,4 +425,47 @@ mod tests {
         assert_eq!(pkt.to_bytes().len(), SYNC_PACKET_SIZE);
         assert_eq!(SYNC_PACKET_SIZE, 32);
     }
+
+    /// ADR-110 iter 21 — cross-language wire-format conformance gate.
+    ///
+    /// These exact bytes are ALSO pinned in the Python test
+    /// `test_canonical_wire_bytes_match_rust_decoder` in
+    /// `archive/v1/tests/unit/test_esp32_binary_parser.py`. If this
+    /// canonical hex stops matching what Python emits for the same
+    /// SyncPacket fields, ONE of the decoders has drifted from the wire.
+    ///
+    /// Canonical packet: COM9 sync-pkt #1 from §A0.12 live capture.
+    #[test]
+    fn canonical_wire_bytes_match_python_decoder() {
+        // Exact bytes matching the Python pin (hex-decoded by hand to bytes).
+        let canonical: [u8; 32] = [
+            0x10, 0xa1, 0x11, 0xc5,  // magic 0xC511A110 (LE u32)
+            0x09,                     // node_id = 9
+            0x01,                     // proto_ver = 1
+            0x06,                     // flags: bit1=is_valid, bit2=smoothed_used
+            0x00,                     // reserved
+            0xf2, 0x6d, 0xb7, 0x01, 0x00, 0x00, 0x00, 0x00,  // local_us = 28_798_450
+            0xc5, 0xac, 0xa5, 0x01, 0x00, 0x00, 0x00, 0x00,  // epoch_us = 27_634_885
+            0x14, 0x00, 0x00, 0x00,  // sequence = 20
+            0x00, 0x00, 0x00, 0x00,  // reserved
+        ];
+        let decoded = SyncPacket::from_bytes(&canonical).unwrap();
+        assert_eq!(decoded.node_id, 9);
+        assert_eq!(decoded.proto_ver, 1);
+        assert_eq!(decoded.flags.to_byte(), 0x06);
+        assert!(!decoded.flags.is_leader);
+        assert!(decoded.flags.is_valid);
+        assert!(decoded.flags.smoothed_used);
+        assert_eq!(decoded.local_us, 28_798_450);
+        assert_eq!(decoded.epoch_us, 27_634_885);
+        assert_eq!(decoded.sequence, 20);
+        // §A0.10's measured 1.16-second boot delta.
+        assert_eq!(decoded.local_minus_epoch_us(), 1_163_565);
+
+        // Round-trip: re-encoding the decoded struct must produce the same
+        // canonical bytes — this is what catches any drift in to_bytes.
+        let re_encoded = decoded.to_bytes();
+        assert_eq!(re_encoded, canonical,
+                   "Rust to_bytes drifted from the canonical pin — Python decoder will break");
+    }
 }