Set callback slot to 0 before executing script

src/quark-core/src/QuarkWallet.sol

@@ -503,6 +503,9 @@ contract QuarkWallet is IERC1271 {
             // Transiently store the active submission token
             tstore(activeSubmissionTokenSlot, submissionToken)
 
+            // Transiently set the callback slot to 0
+            tstore(callbackSlot, 0)
+
             // Note: CALLCODE is used to set the QuarkWallet as the `msg.sender`
             success :=
                 callcode(gas(), scriptAddress, /* value */ 0, add(scriptCalldata, 0x20), scriptCalldataLen, 0x0, 0)

test/lib/GetCallbackDetails.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: BSD-3-Clause
+pragma solidity 0.8.27;
+
+import {QuarkWalletMetadata} from "quark-core/src/QuarkWallet.sol";
+import {QuarkScript} from "quark-core/src/QuarkScript.sol";
+
+contract GetCallbackDetails is QuarkScript {
+    function getCallbackAddress() public returns (address) {
+        bytes32 callbackSlot = QuarkWalletMetadata.CALLBACK_SLOT;
+        address callbackAddress;
+        assembly {
+            callbackAddress := tload(callbackSlot)
+        }
+        return callbackAddress;
+    }
+}

test/quark-core/Callbacks.t.sol

@@ -138,9 +138,44 @@ contract CallbacksTest is Test {
         // gas: meter execute
         vm.resumeGasMetering();
         aliceWallet.executeQuarkOperation(parentOp, v, r, s);
+
         assertEq(counter.number(), 11);
     }
 
+    function testNestedCallbackResetsCallbackSlot() public {
+        // gas: do not meter set-up
+        vm.pauseGasMetering();
+        bytes memory getCallbackDetails = new YulHelper().getCode("GetCallbackDetails.sol/GetCallbackDetails.json");
+        bytes memory executeOtherScript =
+            new YulHelper().getCode("ExecuteOtherOperation.sol/ExecuteOtherOperation.json");
+
+        QuarkWallet.QuarkOperation memory nestedOp = new QuarkOperationHelper().newBasicOpWithCalldata(
+            aliceWallet, getCallbackDetails, abi.encodeWithSignature("getCallbackAddress()"), ScriptType.ScriptAddress
+        );
+
+        (uint8 v_, bytes32 r_, bytes32 s_) = new SignatureHelper().signOp(alicePrivateKey, aliceWallet, nestedOp);
+
+        QuarkWallet.QuarkOperation memory parentOp = new QuarkOperationHelper().newBasicOpWithCalldata(
+            aliceWallet,
+            executeOtherScript,
+            abi.encodeWithSelector(ExecuteOtherOperation.run.selector, nestedOp, v_, r_, s_),
+            ScriptType.ScriptAddress
+        );
+
+        parentOp.nonce = new QuarkOperationHelper().incrementNonce(nestedOp.nonce);
+
+        (uint8 v, bytes32 r, bytes32 s) = new SignatureHelper().signOp(alicePrivateKey, aliceWallet, parentOp);
+
+        // gas: meter execute
+        vm.resumeGasMetering();
+        bytes memory result = aliceWallet.executeQuarkOperation(parentOp, v, r, s);
+        // We decode twice because the result is encoded twice due to the nested operation
+        address innerCallbackAddress = abi.decode(abi.decode(result, (bytes)), (address));
+
+        // The inner callback address should be 0
+        assertEq(innerCallbackAddress, address(0));
+    }
+
     function testNestedCallWithNoCallbackSucceeds() public {
         // gas: do not meter set-up
         vm.pauseGasMetering();