Implement a UUPS-upgradeable counter in two versions with ERC-7201 namespaced storage, tested through an ERC-1967 proxy, with an independent review. Local tests only: never deployed (the IdentityMD launch factory forbids proxies; this job exercises the pattern). Workspace: the job starts from an empty tree (no foundry.toml, forge-std or OpenZeppelin) and each worker may write only the listed src files and their test/.t.sol files, so no dependency can be added. Write everything inline (pragma ^0.8.24, default forge layout, no imports beyond these files); mocks and helper contracts live inside the test files, which declare the cheatcodes they use in an inline Vm interface at the HEVM address and assert with require. So the upgrade machinery is hand-written, mirroring OpenZeppelin v5 UUPSUpgradeable, Initializable and OwnableUpgradeable (same error names), not imported.

src/CounterV1.sol holds abstract UUPSBase and CounterV1. UUPSBase keeps owner and initialized version in ERC-7201 namespace "slam100.storage.Base" and provides: modifiers initializer and reinitializer(uint64) (InvalidInitialization when the version is not higher), _disableInitializers() (version = max), onlyOwner (OwnableUnauthorizedAccount(caller)), onlyProxy (UUPSUnauthorizedCallContext when called on the implementation itself, i.e. address(this) == the immutable self address or the ERC-1967 implementation slot does not point to self), proxiableUUID() returning the ERC-1967 implementation slot and callable only when not delegated, and upgradeToAndCall(newImpl, data) onlyProxy onlyOwner: it requires newImpl to return that slot from proxiableUUID (UUPSUnsupportedProxiableUUID, or ERC1967InvalidImplementation for an address with no code or a reverting call), writes the slot, emits Upgraded and delegatecalls data when non-empty.

CounterV1: state is one struct CounterStorage { uint256 count; } in namespace "slam100.storage.Counter" at keccak256(abi.encode(uint256(keccak256("slam100.storage.Counter")) - 1)) & ~bytes32(uint256(0xff)), a constant annotated @custom:storage-location erc7201:slam100.storage.Counter. constructor() calls _disableInitializers(). initialize(address initialOwner) initializer, zero owner reverts. increment() adds 1 and emits Incremented(newCount); count(); version() returns 1.

CounterV2 (src/CounterV2.sol, imports UUPSBase from CounterV1.sol): same namespace, struct extended only by appending: CounterStorage { uint256 count; uint256 step; }. initializeV2(uint256 step_) reinitializer(2) onlyOwner, step_ >= 1, meant to run inside upgradeToAndCall. increment() adds step, treating 0 as 1 so a proxy upgraded without the call still counts; setStep(uint256) onlyOwner, >= 1; version() returns 2.

Tests: a minimal ERC-1967 proxy inside test/CounterV1.t.sol (constructor(impl, data) writes the slot and delegatecalls data; fallback delegates). Deploy V1 behind it with initialize data; increment; upgradeToAndCall to V2 with initializeV2 and check count, owner and step survive; a non-owner upgrade reverts OwnableUnauthorizedAccount; initialize or initializeV2 on either implementation reverts InvalidInitialization; no initializer runs twice on the proxy; initializeV2 from a non-owner reverts; the test-computed slot equals the constant and vm.load(proxy, slot) / slot + 1 read count and step; upgrading to a contract with the wrong proxiableUUID or an address with no code reverts; upgradeToAndCall called on the implementation directly reverts; the implementation slot holds V2 afterwards.

Review focus: collisions between the two namespaces and with the ERC-1967 slots, initializer front-running on the implementation and on a proxy deployed without init data, upgrade authorization and the onlyProxy check, and whether V1 -> V2 -> V1 corrupts state (document it).