test flow() atomicity on later-transfer failure

test/src/concrete/Flow.transfer.t.sol

@@ -428,4 +428,53 @@ contract FlowTransferTest is FlowTest {
         flow.flow(evaluable, new uint256[](0), new SignedContextV1[](0));
         vm.stopPrank();
     }
+
+    /// `IFlowV5.flow()` MUST process the flow atomically. When a later
+    /// transfer fails, the entire flow MUST revert and earlier transfers
+    /// must NOT have observable side effects. With mocks, we observe this
+    /// by asserting the outer revert (transaction revert rolls back any
+    /// state) and that the failing transfer's selector is the revert
+    /// reason — i.e. the inner failure was not caught and squashed.
+    /// forge-config: default.fuzz.runs = 100
+    function testFlowAtomicRollbackOnLaterTransferFailure(
+        address alice,
+        address bob,
+        uint256 erc20Amount,
+        uint256 erc1155TokenId,
+        uint256 erc1155Amount
+    ) external {
+        vm.assume(alice != address(0));
+        vm.assume(bob != alice);
+        vm.assume(Sentinel.unwrap(RAIN_FLOW_SENTINEL) != erc20Amount);
+        vm.assume(Sentinel.unwrap(RAIN_FLOW_SENTINEL) != erc1155TokenId);
+        vm.assume(Sentinel.unwrap(RAIN_FLOW_SENTINEL) != erc1155Amount);
+        vm.label(alice, "Alice");
+        vm.label(bob, "Bob");
+
+        (IFlowV5 flow, EvaluableV2 memory evaluable) = deployFlow();
+        assumeEtchable(alice, address(flow));
+        assumeEtchable(bob, address(flow));
+
+        // ERC20 from alice → flow (would succeed); ERC1155 from bob → alice
+        // (will revert because `bob` is neither `msg.sender` nor `flow`).
+        ERC20Transfer[] memory erc20Transfers = new ERC20Transfer[](1);
+        erc20Transfers[0] = ERC20Transfer({token: TOKEN_A, from: alice, to: address(flow), amount: erc20Amount});
+
+        ERC1155Transfer[] memory erc1155Transfers = new ERC1155Transfer[](1);
+        erc1155Transfers[0] =
+            ERC1155Transfer({token: TOKEN_C, from: bob, to: alice, id: erc1155TokenId, amount: erc1155Amount});
+
+        uint256[] memory stack = LibStackGeneration.generateFlowStack(
+            Sentinel.unwrap(RAIN_FLOW_SENTINEL),
+            FlowTransferV1(erc20Transfers, new ERC721Transfer[](0), erc1155Transfers)
+        );
+        interpreterEval2MockCall(stack, new uint256[](0));
+
+        vm.mockCall(TOKEN_A, abi.encodeWithSelector(IERC20.transferFrom.selector), abi.encode(true));
+
+        vm.startPrank(alice);
+        vm.expectRevert(UnsupportedERC1155Flow.selector);
+        flow.flow(evaluable, new uint256[](0), new SignedContextV1[](0));
+        vm.stopPrank();
+    }
 }