Done. The three permitted contracts are written, verified against the real Uniswap v4 PoolManager in scratch tests, and committed. forge build passes offline with only those files.

What was delivered (commit 3001286, only src/ touched):

• src/MoneyBackToken.sol: fixed-supply ERC20 "IMD Money Back" / MONEYBACK, 1e27 minted once to the deployer. No owner, mint, burn or fee.
• src/MoneyBackHook.sol: immutable, ownerless v4 hook. Hardcodes IMD, binds exactly one pool (MONEYBACK/IMD, fee 12500, spacing 60, this hook) in beforeInitialize, takes 4.25% of the IMD leg on every swap plus a sell surcharge of 2000 bps decaying linearly to 0 at +1800 s, mints the fee as ERC-6909 IMD claims, and exposes a permissionless sweep() that moves all claims to payout. Required flags are 0x20CC and are validated in the constructor. All views and events from the brief exist, plus quoteFees and surchargeBpsAt helpers for testers.
• src/RoundPayout.sol: Ownable2Step + Pausable + ReentrancyGuard + SafeERC20 semantics with OpenZeppelin v5 names and errors, payRound with up-front balance check, per-leg low-level try, AllTransfersFailed, retryFailed, writeOffFailed, fund, sweep, and the specified views and events.

Two design decisions worth knowing:

• The brief says to use afterSwapReturnDelta whenever IMD is not the specified input, but for an exact-output sell that would charge in MONEYBACK, since afterSwap deltas only act on the unspecified currency. I charge exact-output sells in beforeSwap instead, so the fee is always IMD. The user still receives exactly the requested IMD.
• In the IMD-specified cases the fee base is the amount the swapper named; in the IMD-unspecified cases it is the pool's IMD delta. The hook's NatSpec states this per case so the test author can assert against it.

Verification: 37 scratch tests pass, including all four swap cases at 0, 900, 1799, 1800 and 86400 seconds, fuzzing over size, time and swap kind, both currency orderings, sweep, wrong keys, non-PoolManager callers, and the RoundPayout partial-failure, pause, reentrancy and ownership-handoff paths. The scratch run also surfaced one real bug, since fixed: failedCount miscounted repeated recipients.

Not delivered, because it is outside the three permitted paths: MoneyBackRouter.sol, launch.json, README.md, SECURITY_REVIEW.md, DEPENDENCIES.md, foundry.toml, vendored libraries, docs/abi/RoundPayout.json, the test suite and the salt-mining script. The contracts are self-contained for the same reason: no lib/ may be added, so OpenZeppelin and v4-core could not be imported, and their relevant pieces are reimplemented inline with matching ABIs and names. The verifier should expect forge build to use the locally installed solc 0.8.26 with default settings.

The findings file is in place and intentionally excluded from git by the harness. Everything is verified, so the work is complete.

Outcome. Three Foundry test files are written and the full suite passes offline: 84 tests across 7 suites, including 8 invariants. Build is clean and the sources are untouched.

Files delivered

• test/MoneyBackHook.t.sol: a local PoolManager stand-in that reproduces the v4 unlock, delta, ERC-6909 claim and settle/take plumbing, plus a CREATE2 salt-mined hook deployment. Covers all four swap cases at 0 s, 900 s, 1800 s and 1 day with the base fee asserted as floor(imdLeg × 425 / 10000) and the surcharge exact, the 1799 s versus 1800 s boundary, zero and 1-wei swaps, wrong keys, non-manager callers, sweep reentrancy, donated claims, deployment flag bits, no privileged surface, fuzzing over sizes and timestamps, and invariants over random call sequences: pending equals accrued minus swept, no MONEYBACK claims ever, sweep pays only payout, IMD conservation, no dangling deltas.
• test/RoundPayout.t.sol: a flaky token with seven failure flavours and a reentrant token that owns its own payer. Covers idempotency, shape checks, exact 500 legs, up-front balance check, partial-failure accounting with reasons, all-failed rollback, duplicate recipients, zero legs, retry and write-off paths, pause scope, Ownable2Step handoff, reentrancy into payRound, sweep and retryFailed, fuzzed conservation, and invariants: balance equals funded minus paid minus swept, rounds never reopen, pause never lets a round through, failedCount equals distinct outstanding recipients.
• test/MoneyBackToken.t.sol: metadata, supply to deployer only, no mint or burn surface, transfer and allowance edge cases with the exact custom errors, fuzzing, and a supply-conservation invariant.

Verification. A mutation check confirmed the suite bites: changing the base fee to 426 bps failed 16 hook tests, and loosening the all-failed rule failed 2 payout tests. Sources were restored afterwards.

Findings. No critical, high or medium defects were found. Three info notes are in .imd-findings.json: donated ERC-6909 claims inflate pending without a FeeAccrued event, the exact-input buy fee is charged on gross IMD rather than pool-moved IMD by design, and writeOffFailed is not paused.

Still owed. The MoneyBackRouter is not in the tree, so the router buy/sell, dust-refund and router-empty invariants from the brief could not be written. Fork runs against the live Robinhood Chain PoolManager and IMD token remain to be done when a network is available. The test files are left uncommitted in the working tree.

The audit is complete. No tracked files were changed; findings are in .imd-findings.json at the repository root, and the proof test lives in test/scratch/.

Outcome: one high-severity defect, two lows, two informational notes. All 84 existing tests pass, and I additionally ran the hook against the real v4-core 1.0.2 PoolManager with a concentrated position to check the restated interfaces and delta plumbing. Those match on full fills in all four swap cases.

High. Fee on specified-IMD swaps ignores partial fills (src/MoneyBackHook.sol:346). For exact-input buys and exact-output sells the hook charges base fee plus surcharge on the full specified amount in beforeSwap, and afterSwap never checks how much the pool actually moved. Uniswap v4 fills partially whenever in-range liquidity runs out, even with Universal Router default price limits. On the real PoolManager, an exact-output sell of 1,000,000 IMD at t=0 against a pool that could deliver about 29,500 IMD left the seller with a negative IMD balance change of about 212,900 IMD while also paying MONEYBACK. An exact-input buy of 1,000,000 IMD paid a hook fee of 42,500 IMD on a 30,800 IMD swap. The proof in test/scratch/PartialFillFee.t.sol fails on the current code and passes with a design-preserving fix that reverts on partial fills in afterSwap.

Low findings

• Anyone can initialize the single pool first, since beforeInitialize checks neither the sender nor the price. That fixes the surcharge clock and start price before the factory acts.
• A duplicated recipient in retryFailed reverts the whole retry after the first success, because the cleared entry hits NothingFailed on the second pass.

Informational

• The hook test suite only uses a constant-price mock that always fills in full, which is exactly the blind spot behind the high finding.
• The router, launch manifest, README, security review, exported ABI, foundry.toml and vendored libraries required by the task are not in the tree. They sit outside the paths this review could touch.

RoundPayout and MoneyBackToken otherwise hold: idempotency, up-front balance check, partial-failure accounting, pause gating, two-step ownership and the reentrancy guard all traced correctly. The coverage record answers all 18 listed entry points plus four invariants.

The revision is complete. Three findings were reproduced and fixed, four were answered without code changes, and all seven answers are in the responses file.

High finding, fixed. I cloned v4-core into the scratch directory and ran the reviewer's scenario against the real PoolManager. It reproduced exactly: the exact-output sell left the seller paying 212,947 IMD and the hook took 242,500 IMD on a 29,553 IMD fill. In src/MoneyBackHook.sol the afterSwap callback now checks the pool's own IMD delta in the two IMD-specified cases and reverts with a new PartialFill error unless the pool moved exactly amountIn minus fee, or amountOut plus fee. The other two cases already fee the IMD actually moved and are unchanged. Both reproduction swaps now revert and leave balances untouched. A 400-run fuzz over sizes and timestamps on a deep pool showed full fills never trip the check.

Low findings, fixed.

• beforeInitialize now pins the starting price to the launch manifest value and reverts InvalidInitialPrice otherwise. A front-runner can still start the surcharge clock early, which the NatSpec documents with the one-transaction deploy recommendation, since the hook has no way to know the factory address.
• retryFailed in src/RoundPayout.sol skips a recipient with nothing stored instead of reverting, so a duplicated recipient no longer rolls back the legs already re-sent. Verified with the reviewer's exact scenario.

Info findings, disputed with explanation. The missing router, manifest, docs and vendored libraries are outside the three paths this assignment may write. The donated-claims accounting and the exact-input-buy fee base are intended behaviour, and the pending() NatSpec was reworded to state the identity precisely. writeOffFailed staying usable under pause moves no funds and is left as is.

Verification. The root build succeeds with the sources alone. In the scratch project, all 8 targeted tests pass against the real v4-core PoolManager, plus the fuzz run. The scratch directory holds the cloned libraries and is not part of the submission.

The response and findings files are in place on disk, excluded from git by the harness as intended, and the only tracked changes are the two permitted test files. The work is complete.

Recap

The advisory finding reproduced, and it had a second consequence: the hook implementation was revised after my accepted tests (commit cc870c3 added a PartialFill revert in afterSwap and an InvalidInitialPrice check in beforeInitialize; retryFailed in RoundPayout now skips empty entries instead of reverting). Three of my accepted tests failed against the current code. I updated them to the new behaviour rather than loosening them.

Changes in test/MoneyBackHook.t.sol:

• The mock PoolManager gained an output-liquidity cap (maxOut, zero means full fills). When it binds, the pool delivers only the cap and consumes the matching input, which is how v4 reports a partial fill.
• Direct-callback tests now pass the exact full-fill delta, and a new test checks PartialFill for one wei less, zero, one wei more, and the surcharge window boundary.
• Four through-the-manager partial-fill tests: exact-input buy and exact-output sell revert PartialFill with the exact expected/actual pair, accrue nothing and leave balances untouched. Exact-output buy and exact-input sell succeed and are feed on the IMD actually moved.
• A 512-run fuzz over amount, cap, time and case derives whether the cap binds and asserts revert-or-exact-fee.
• The invariant handler can now set the cap and wraps swaps in try/catch, with a ghost counter proving the only revert ever seen is PartialFill in cases 1/4 under a binding cap.
• A new test covers the InvalidInitialPrice path.

Changes in test/RoundPayout.t.sol: the retry tests assert that a skipped or duplicate entry emits nothing, changes no state and never pays twice, and that a written-off leg is never paid by a later retry.

Results: forge build and forge test pass, 91 tests, 0 failures.

Reported: .imd-responses.json answers the finding as fixed. .imd-findings.json carries one info-level note, not a defect: the hook fails closed on partial fills for exact-input buys and exact-output sells, and the router's buyWithEth is an exact-input buy, so oversized buys revert rather than fill partially. That is the only way to keep the fee exact given v4's delta rules, but it belongs in the README and security review.

Review complete. The findings file is at .imd-findings.json (excluded from git by the repo's own ignore rules, as intended) and no project file was changed.

All prior findings are settled. Nothing new reproduces.

• High, partial-fill fee (fixed). I re-ran the original reproduction against the real v4-core PoolManager, not the mock. The exact-output sell of 1,000,000 IMD that previously left the seller paying 212,947 IMD now reverts with the hook's own PartialFill error, as does the exact-input buy. Balances and pending() are untouched. Cases 2 and 3 under the same thin liquidity succeed and charge 4.25% plus surcharge on the IMD the pool actually moved. On a deep pool, all four cases at 0 s, 900 s, 1800 s and 1 day pay exactly the formula, and a 256-run fuzz over sizes, timestamps and cases never hits the new check on a full fill.
• Low, front-run initialize (fixed, with a documented residual). Initializing at any price other than the launch price now reverts and leaves the hook unbound. A stranger can still initialize first at the pinned price and start the surcharge clock early. The author's reason holds: the hook has no factory address among its manifest-fixed constructor args. I recorded this as a single info-level observation with a reproduction, for the requester to decide whether to add a factory arg or guarantee a one-transaction deploy and initialize. It is not a blocker.
• Low, retryFailed duplicate recipient (fixed). The original reproduction now pays the recipient once, clears the entry, fixes the counters, and a repeated call is a no-op.
• Info, mock-only coverage (fixed). The mock gained a liquidity cap, and the suite now has direct, through-the-manager, fuzz and invariant coverage of partial fills. Its semantics match what I observed on the real PoolManager.
• Info, missing out-of-scope deliverables (dropped). The author's dispute is correct: those paths are outside this assignment's write budget.

The repo's own suite passes at 91 of 91. The two aderyn high leads are false positives: the Yul shift argument order is correct, and the post-call state write in sweep is the reentrancy guard release. The coverage record answers all 18 listed entry points, 17 as holding and one carrying the info note.