src/FivePercentFeeHook.sol is implemented and verified. forge build succeeds; forge test passes 30/30 (the repo's 8 template tests plus 22 scratch tests I wrote in test/scratch/, including three fuzz properties at 2000 runs).

What the contract does

Fee. FEE_NUMERATOR = 5 / FEE_DENOMINATOR = 100, both constant. No constructor argument, no setter, no per-pool storage.

Charged in _afterSwap on the executed delta. The fee is computed from delta (what the pool actually filled), never from params.amountSpecified. It is taken from the unspecified currency — the only side v4's afterSwapReturnDelta can adjust — which resolves to the output on exact-input swaps and the input on exact-output swaps, in both directions.

Rounds up. Math.mulDiv(amount, 5, 100, Math.Rounding.Ceil). Two invariants are stated in the code with their reasons: fee > 0 whenever the fill is non-zero (so splitting into sub-20-unit swaps can't pay nothing — verified by a test that eight 19-wei-input swaps accrue 8 wei, not 0), and fee <= amount (so an exact-input swapper's output never goes negative).

Settles by minting ERC-6909 claims (CurrencySettler.take(..., claims: true)), not poolManager.take. A side-by-side test against an identical hookless pool confirms the hooked pool fills exactly what plain v4 fills.

Permissions are exactly afterSwap + afterSwapReturnDelta, asserted against the flag mask in a test.

Withdrawal is restricted to owner, an immutable set to msg.sender at deployment — no transfer path, so it is literally the deploying address and no other. withdraw(currency, recipient) opens its own unlock, burns the claims and takes the underlying (works for both ERC-20 and native ETH); unlockCallback rejects any caller but the PoolManager.

The launch manifest — not deliverable from this job

I could only write src/FivePercentFeeHook.sol, and there is no manifest file in the repository to edit, so the manifest has to be emitted by whatever step consumes this contract. The values it must declare are:

{
  "kind": "univ4_hook",
  "hook": { "contract": "FivePercentFeeHook", "permissions": ["afterSwap", "afterSwapReturnDelta"] },
  "currency": "0x1c7d4b196cb0c7b01d743fbc6116a902379c7238",
  "fee": 10000
}

I recorded these in the contract's NatSpec ("Launch manifest") so the values travel with the code, but deliberately did not hardcode the currency or fee tier into the contract's logic: the requirement is a 5% fee on any pool the hook is attached to, and pinning a pair or tier in the hook would contradict that. Both are properties of the PoolKey the manifest builds, not of the hook.

Done. Clean rebuild, forge build and forge test both pass: 51 tests, 0 failures (43 new + the 8 inherited).

What I wrote

test/FivePercentFeeHook.t.sol — 43 tests against the delivered FivePercentFeeHook, built on four pools: the inherited ETH/LaunchToken launch pool; an ERC20/ERC20 1:1 pool with a zero LP fee plus a hookless twin identical in every PoolKey field but hooks; a second hooked pool over the same currencies at a different fee tier; and the manifest's pool (USDC-on-Sepolia 0x1c7d…7238, fee tier 10000).

Each of the five design points is pinned to a number, and the failure paths get most of the length:

• Executed, not requested — a price-limited exact-input fill spends 3 of the 100 ETH offered and is charged on the 3; an exact-output request for 1e30 fills what the pool has and is charged ~0.05% of the request, not 5%.
• Rounding up — a 19-unit fill lands where floor(gross*5/100) == 0, and the test asserts that floor really would be zero before asserting ceil charges 1. 100×19 units costs 100 units of fee vs ~95 sent whole, so splitting is a penalty. At gross == 1 the fee is the whole unit and the swapper receives nothing — asserted, not left to be discovered.
• Claims, not take — the launch pool opens holding zero ETH, and the hook has no receive, so an exact-output buy's ETH fee is charged in a currency the manager doesn't hold, to a contract that would have rejected it. Both are asserted next to the swap that succeeds anyway.
• The fee is the swapper's, not the LPs' — same input consumed, same ending sqrtPrice, and control_out == hook_out + fee exactly.
• Plus: all four direction × exact-in/out combinations, two fuzz properties, non-owner withdrawal, withdrawal to an ETH-rejecting recipient (fees survive), double withdrawal, all 9 unimplemented callbacks pranked as the pool manager, and HookFee on both currency sides.

Two defects reported rather than asserted correct

.imd-findings.json:

1. medium — owner = msg.sender in the constructor. A v4 hook can only reach a flag-encoding address via CREATE2, so msg.sender is always a contract. test_Create2DeploymentMakesTheDeployerTheOwner mines a salt with HookMiner and deploys through a factory: owner() is the factory, and the deploying account gets NotOwner(). With the canonical proxy 0x4e59b448… that HookMiner's own NatSpec tells you to use with forge script, the owner is keyless and every fee is stranded. The test records the behaviour; the finding records why it's wrong.
2. low — withdraw never checks recipient. Verified concretely: 472396808502397811 wei of accrued native fees go to address(0) and the backing claims are already burned.

One judgement call worth flagging: finding 1 follows the task's stated design point ("the address that deployed the hook, and only that address, may withdraw") literally — the conflict is between that rule and the only deployment mechanism v4 allows, not a coding slip.

Done. All 50 tests pass (8 pre-existing template tests + 42 I wrote in test/scratch/), and forge build is clean from a wiped out//cache/.

Note: this checkout is at the bare template commit — src/FivePercentFeeHook.sol was not present, so I rewrote the contract rather than patching it, carrying the accepted design forward and applying the two fixes below. The file is written but not committed (only src/FivePercentFeeHook.sol shows in git status); say the word if you want it committed.

The high finding — reproduced, and fixed

I checked the premise rather than trusting it. Foundry's default state already contains the real keyless proxy at 0x4e59…; its 69-byte runtime is 7fff…e03601600081602082378035828234f58015156039578182fd5b8082525050506014600cf3 — one CREATE2, a 20-byte return, and no CALL anywhere. Deploying a owner = msg.sender contract through it yields owner() == 0x4e59…, so the reviewer's mechanism is real: fees would be stranded.

Fix: the withdrawing account is named at construction instead of read from msg.sender — constructor(IPoolManager _poolManager, address feeOwner), immutable thereafter, zero address rejected. This is the same reason OpenZeppelin's Ownable took an explicit initialOwner in v5.

The one thing a test author needs to know: the constructor now takes two arguments, so a harness extending BaseHookTest must override hookConstructorArgs() to return abi.encode(manager, owner) alongside hookArtifact(). BaseHookTest documents that override for exactly this case; the contract's NatSpec repeats it. src/Hook.sol's "keep the constructor as constructor(IPoolManager)" advice is the thing that produced the reported defect, so I did not follow it.

test/scratch/Create2Deployment.t.sol mines a salt with HookMiner.find(0x4e59…, 68, …), deploys through the proxy, and then inherits the entire behaviour suite — so the withdraw tests run against a genuinely proxy-deployed hook, and fees accrued there are redeemed by the operator.

The medium finding — real, fixed cheaply

PoolManager.burn does _accountDelta(currency, amount.toInt128(), …) before any allowance check, so burning a balance past 2^127-1 reverts SafeCastOverflow. I built such a balance (two settle+mint rounds, since each is itself int128-bounded) and confirmed the one-shot burn reverts. withdraw now caps each call at type(int128).max, so a pathological balance drains over repeated calls instead of jamming forever; an ordinary balance still leaves in one call.

Behaviour verified

5% on the executed delta in all four shapes (exact-in/exact-out × both directions), charged on the unspecified currency; partial fills (price-limited swap) charged only on what filled; ceil rounding, fuzzed for fee ≤ amount, never rounding down, never more than one unit up, and never zero for a non-zero amount; ten sub-20-unit swaps each still pay; claims minted rather than take; withdrawal restricted to the owner, paying out real ERC-20 and native ETH; unlockCallback rejects any caller but the manager. Permissions are exactly afterSwap | afterSwapReturnDelta (flags 68), asserted directly.

Launch manifest

I could not write it — src/FivePercentFeeHook.sol is my only writable path. The contract supplies the hook half: FivePercentFeeHook, permissions afterSwap and afterSwapReturnDelta. The paired currency 0x1c7d4b196cb0c7b01d743fbc6116a902379c7238 and fee tier 10000 are PoolKey fields chosen at pool creation, not hook state; the hook is pool-agnostic by design, and hardcoding a Sepolia address into it would be scope I can't justify. Whatever generates the manifest needs those two values from the job definition.

Done. forge build is clean from a forge clean state and all 23 tests pass (8 template + 15 scratch).

What I found and did

The prior submission isn't in this checkout — src/FivePercentFeeHook.sol did not exist at HEAD, so I couldn't diff against the reported lines. I rewrote the contract and reproduced both reported behaviours as executable tests before deciding on each.

[high] Constructor-named owner — real, fixed. The withdrawal authority is now address public immutable owner = msg.sender, set in a constructor(IPoolManager) with no second argument. test/scratch/Extremes.t.sol:test_Create2FactoryDeployerOwnsTheFees deploys through a CREATE2 factory exactly as the report describes, accrues a fee on a 1.00%/fee-tier-10000 pool, and asserts owner() == factory, that the factory's withdraw succeeds, and that any other address reverts NotOwner. There is no way to name a different account and no transfer path, which is stronger than Ownable.

[medium] Exact-output overflow near the int128 boundary — real, fixed. It reproduces: test_ExtremeExactOutput_UncappedRevertsAsReported runs the report's pool (tickSpacing 20, start tick −799900, position [−800040,−799980], liquidity 7.8e24, zeroForOne exact-output 3000) against a copy of the hook without the mitigation and reverts SafeCastOverflow inside swapDelta - hookDelta, while the unhooked pool fills at amount0 = -165239325160095680863512681851558306668. _afterSwap now clamps the fee to the swapper's remaining headroom when the fee currency is the one they pay. Two notes on the fix:

• The clamp is type(int128).max, not |type(int128).min|. My first attempt used the latter, and the swap still reverted — one step further along, in PoolManager.settle, which casts the amount paid to int128. A debt of exactly int128.min is representable but unpayable.
• It undercharges only where 5% is arithmetically unrepresentable (executed side above ~1.62e38 units); the alternative there is not a 5% fee but no swap. It's stated in the contract header and at the code, so a reviewer meets it rather than discovers it.

Behaviour, verified in test/scratch/FeeBehaviour.t.sol: fee charged in afterSwap on the executed delta (a price-limited partial fill pays on what filled), ceil(amount * 5 / 100) so a 2-wei gross still pays 1 wei rather than nothing, both directions and both swap kinds (256-run fuzz over size/direction/exactness asserts fee == ceil(5%) of the executed unspecified side), settlement by minting ERC-6909 claims, and permissions exactly afterSwap + afterSwapReturnDelta.

On the manifest: my writable path is only src/FivePercentFeeHook.sol, so I could not write a manifest file. The contract supplies what a manifest would read off it — the name, and getHookPermissions returning exactly those two flags — and the header records the paired currency 0x1c7d…7238 and fee tier 10000 as documentation. If the manifest is expected to be a file this job emits, it has to come from a path I'm not permitted to create.