feat(evm): add grant management for EVM wallets

useragent/lib/features/connection/evm/grants.dart

@@ -0,0 +1,122 @@
+import 'package:arbiter/features/connection/connection.dart';
+import 'package:arbiter/proto/evm.pb.dart';
+import 'package:arbiter/proto/user_agent.pb.dart';
+import 'package:fixnum/fixnum.dart';
+import 'package:protobuf/well_known_types/google/protobuf/timestamp.pb.dart';
+
+Future<List<GrantEntry>> listEvmGrants(
+  Connection connection, {
+  int? walletId,
+}) async {
+  final request = EvmGrantListRequest();
+  if (walletId != null) {
+    request.walletId = walletId;
+  }
+
+  await connection.send(UserAgentRequest(evmGrantList: request));
+
+  final response = await connection.receive();
+  if (!response.hasEvmGrantList()) {
+    throw Exception(
+      'Expected EVM grant list response, got ${response.whichPayload()}',
+    );
+  }
+
+  final result = response.evmGrantList;
+  switch (result.whichResult()) {
+    case EvmGrantListResponse_Result.grants:
+      return result.grants.grants.toList(growable: false);
+    case EvmGrantListResponse_Result.error:
+      throw Exception(_describeGrantError(result.error));
+    case EvmGrantListResponse_Result.notSet:
+      throw Exception('EVM grant list response was empty.');
+  }
+}
+
+Future<int> createEvmGrant(
+  Connection connection, {
+  required int clientId,
+  required int walletId,
+  required Int64 chainId,
+  DateTime? validFrom,
+  DateTime? validUntil,
+  List<int>? maxGasFeePerGas,
+  List<int>? maxPriorityFeePerGas,
+  TransactionRateLimit? rateLimit,
+  required SpecificGrant specific,
+}) async {
+  await connection.send(
+    UserAgentRequest(
+      evmGrantCreate: EvmGrantCreateRequest(
+        clientId: clientId,
+        shared: SharedSettings(
+          walletId: walletId,
+          chainId: chainId,
+          validFrom: validFrom == null ? null : _toTimestamp(validFrom),
+          validUntil: validUntil == null ? null : _toTimestamp(validUntil),
+          maxGasFeePerGas: maxGasFeePerGas,
+          maxPriorityFeePerGas: maxPriorityFeePerGas,
+          rateLimit: rateLimit,
+        ),
+        specific: specific,
+      ),
+    ),
+  );
+
+  final response = await connection.receive();
+  if (!response.hasEvmGrantCreate()) {
+    throw Exception(
+      'Expected EVM grant create response, got ${response.whichPayload()}',
+    );
+  }
+
+  final result = response.evmGrantCreate;
+  switch (result.whichResult()) {
+    case EvmGrantCreateResponse_Result.grantId:
+      return result.grantId;
+    case EvmGrantCreateResponse_Result.error:
+      throw Exception(_describeGrantError(result.error));
+    case EvmGrantCreateResponse_Result.notSet:
+      throw Exception('Grant creation returned no result.');
+  }
+}
+
+Future<void> deleteEvmGrant(Connection connection, int grantId) async {
+  await connection.send(
+    UserAgentRequest(evmGrantDelete: EvmGrantDeleteRequest(grantId: grantId)),
+  );
+
+  final response = await connection.receive();
+  if (!response.hasEvmGrantDelete()) {
+    throw Exception(
+      'Expected EVM grant delete response, got ${response.whichPayload()}',
+    );
+  }
+
+  final result = response.evmGrantDelete;
+  switch (result.whichResult()) {
+    case EvmGrantDeleteResponse_Result.ok:
+      return;
+    case EvmGrantDeleteResponse_Result.error:
+      throw Exception(_describeGrantError(result.error));
+    case EvmGrantDeleteResponse_Result.notSet:
+      throw Exception('Grant revoke returned no result.');
+  }
+}
+
+Timestamp _toTimestamp(DateTime value) {
+  final utc = value.toUtc();
+  return Timestamp()
+    ..seconds = Int64(utc.millisecondsSinceEpoch ~/ 1000)
+    ..nanos = (utc.microsecondsSinceEpoch % 1000000) * 1000;
+}
+
+String _describeGrantError(EvmError error) {
+  return switch (error) {
+    EvmError.EVM_ERROR_VAULT_SEALED =>
+      'The vault is sealed. Unseal it before using EVM grants.',
+    EvmError.EVM_ERROR_INTERNAL || EvmError.EVM_ERROR_UNSPECIFIED =>
+      'The server failed to process the EVM grant request.',
+    _ => 'The server failed to process the EVM grant request.',
+  };
+}