feat: Add 7702 Semi-Modular Account Support

src/account/SemiModularAccount.sol

@@ -92,7 +92,7 @@ contract SemiModularAccount is ReferenceModularAccount {
     }
 
     /// @inheritdoc IModularAccount
-    function accountId() external pure override returns (string memory) {
+    function accountId() external pure virtual override returns (string memory) {
         return "erc6900.reference-semi-modular-account.0.8.0";
     }
 
@@ -177,6 +177,7 @@ contract SemiModularAccount is ReferenceModularAccount {
     function _retrieveFallbackSignerUnchecked(SemiModularAccountStorage storage _storage)
         internal
         view
+        virtual
         returns (address)
     {
         address storageFallbackSigner = _storage.fallbackSigner;

src/account/SemiModularAccount7702.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity ^0.8.20;
+
+import {IModularAccount} from "../interfaces/IModularAccount.sol";
+import {SemiModularAccount} from "./SemiModularAccount.sol";
+import {IEntryPoint} from "@eth-infinitism/account-abstraction/interfaces/IEntryPoint.sol";
+
+contract SemiModularAccount7702 is SemiModularAccount {
+    constructor(IEntryPoint anEntryPoint) SemiModularAccount(anEntryPoint) {}
+
+    /// @inheritdoc IModularAccount
+    function accountId() external pure virtual override returns (string memory) {
+        return "erc6900.reference-semi-modular-account-7702.0.8.0";
+    }
+
+    /// @dev If the fallback signer is set in storage, ignore the 7702 signer.
+    function _retrieveFallbackSignerUnchecked(SemiModularAccountStorage storage _storage)
+        internal
+        view
+        override
+        returns (address)
+    {
+        address storageFallbackSigner = _storage.fallbackSigner;
+        if (storageFallbackSigner != address(0)) {
+            return storageFallbackSigner;
+        }
+
+        // To support 7702, we default to address(this) as the fallback signer.
+        return address(this);
+    }
+}