fix(bitbox): sign the registration with a chainId-extended EIP-712 domain

lib/packages/wallet/eip712_signer.dart

@@ -24,11 +24,20 @@ class Eip712Signer {
     required bool swissTaxResidence,
     required String registrationDate,
   }) {
+    // The BitBox02 firmware refuses to sign typed data whose EIP712Domain has
+    // no chainId ("typed data has no chain ID" shown on the device), so
+    // hardware wallets sign with the chainId-extended domain. Software wallets
+    // keep the legacy chainId-less domain until Aktionariat has confirmed its
+    // signature re-verification accepts the extended variant — the API
+    // accepts both (pair PR DFXswiss/api#4542).
+    final includeChainIdInDomain = credentials is BitboxCredentials;
+
     final Map<String, dynamic> typedDataMap = {
       'types': {
         'EIP712Domain': [
           {'name': 'name', 'type': 'string'},
           {'name': 'version', 'type': 'string'},
+          if (includeChainIdInDomain) {'name': 'chainId', 'type': 'uint256'},
         ],
         'RealUnitUser': [
           {'name': 'email', 'type': 'string'},
@@ -47,7 +56,11 @@ class Eip712Signer {
         ],
       },
       'primaryType': 'RealUnitUser',
-      'domain': {'name': 'RealUnitUser', 'version': '1'},
+      'domain': {
+        'name': 'RealUnitUser',
+        'version': '1',
+        if (includeChainIdInDomain) 'chainId': chainId,
+      },
       'message': {
         'email': email,
         'name': name,

test/packages/wallet/eip712_signer_bitbox_test.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'dart:typed_data';
 
 import 'package:bitbox_flutter/bitbox_manager.dart';
@@ -23,9 +24,9 @@ void main() {
   BitboxCredentials connected() =>
       BitboxCredentials('0x000000000000000000000000000000000000dead')..setBitbox(manager);
 
-  Future<String> signRegistration() => Eip712Signer.signRegistration(
+  Future<String> signRegistration({int chainId = 1}) => Eip712Signer.signRegistration(
     credentials: connected(),
-    chainId: 1,
+    chainId: chainId,
     email: 'jk@dfx.swiss',
     name: 'Joshua',
     type: 'human',
@@ -48,6 +49,40 @@ void main() {
       expect(await signRegistration(), '0xcafebabe');
     });
 
+    // The BitBox02 firmware rejects typed data whose EIP712Domain has no
+    // chainId ("typed data has no chain ID" on the device) — hardware-wallet
+    // registrations must sign the chainId-extended domain. The software-wallet
+    // path keeps the legacy domain (pinned by the golden signature in
+    // eip712_signer_test.dart).
+    // Signs with a non-default chainId so a hardcoded value cannot pass, and asserts the
+    // EIP712Domain member list exactly: the domain typehash covers the names, their types
+    // and their order, so any of those drifting changes the digest and the API recovers a
+    // foreign address. Mirrors the chainId-wiring pin in
+    // test/integration/eip7702_delegation_bitbox_test.dart.
+    for (final chainId in const [1, 11155111]) {
+      test('signs with the chainId-extended EIP-712 domain (chainId $chainId)', () async {
+        when(
+          () => manager.signETHTypedMessage(any(), any(), any()),
+        ).thenAnswer((_) async => Uint8List.fromList([0x01]));
+
+        await signRegistration(chainId: chainId);
+
+        // called(1): a second sign would mean a second on-device confirmation prompt.
+        final captured = (verify(
+          () => manager.signETHTypedMessage(captureAny(), any(), captureAny()),
+        )..called(1)).captured;
+        final typedData = jsonDecode(utf8.decode(captured[1] as Uint8List)) as Map<String, dynamic>;
+
+        expect(captured[0], chainId);
+        expect(typedData['domain']['chainId'], chainId);
+        expect(typedData['types']['EIP712Domain'], [
+          {'name': 'name', 'type': 'string'},
+          {'name': 'version', 'type': 'string'},
+          {'name': 'chainId', 'type': 'uint256'},
+        ]);
+      });
+    }
+
     test('throws SigningCancelledException on empty signature', () async {
       when(
         () => manager.signETHTypedMessage(any(), any(), any()),