Release Referral (token symbol REFR) on Sepolia as a univ4_hook launch.

Token: Referral (REFR), total supply 1,000,000,000 REFR with 18 decimals, minted once to the deployer (a separate zero-argument ERC-20, no mint, owner or admin).

Hook: ReferralHook, a Uniswap v4 hook on the token's native-ETH pool that pays referrers.

Referrer: abi.decode(hookData, (address)) when hookData is exactly 32 bytes; it counts only if it is non-zero, not tx.origin (self-referral pays nothing), not the hook and not the PoolManager. A swap with a valid referrer pays 20 bps (0.2%) of its ETH leg with the ETH-leg mechanics below, credited to that referrer's claimable ETH balance; a swap without one pays no hook fee at all.

There is no protocol cut and no owner (the earlier 0.1% to $owner is dropped: no live hook launch has taken $owner). claim() pays msg.sender its whole balance, zeroed first, through the hook's unlockCallback.

Events: Referred(referrer, poolId, ethLeg, reward), Claimed(referrer, amount).

Views: balanceOf(referrer), referredVolume(referrer), referralCount(referrer). Limits for the README: the self-referral check is tx.origin, so a second wallet defeats it, and the 0.2% then just returns to the swapper's own second wallet (no gain, no loss); hookData is unauthenticated, which only lets a swapper choose whom it pays.

ETH-leg fee mechanics (the pattern live launch 170's MedallionHook uses): a buy is zeroForOne (ETH in), a sell is oneForZero (ETH out), and the swapper's specified amount is always honoured exactly.

When ETH is the specified currency (exact-in buys, exact-out sells) the fee is taken in beforeSwap as a positive specified BeforeSwapDelta of floor(|amountSpecified| x bps / 10,000); when ETH is the unspecified currency (exact-out buys, exact-in sells) it is taken in afterSwap as a positive unspecified delta of floor(ETH the pool moved x bps / 10,000). A partial fill (price limit hit) reverts with PartialFill.

The hook settles each fee by minting itself ERC-6909 claims on ETH (poolManager.mint) inside the swap, never take() or an ETH transfer in a callback, so the first buy into the ETH-less pool works; every payout later burns claims and takes ETH inside the hook's own unlockCallback, with the balance zeroed before the take (CEI). A fee that rounds to 0 is 0: dust swaps never revert. Wherever this request says ETH leg, it means that fee base.

Invariant: the hook's ETH claim balance at the PoolManager equals the sum of everything it still owes.

Deploy shape, matching the live Sepolia hook launches 170, 183 and 186 (launch 168 passed the mainnet PoolManager and is not a model): ReferralHook's only constructor argument is the Sepolia PoolManager 0xE03A1074c86CFeDd5C142C4F04F1a1536e203543; every rate, window and threshold here is a source constant; there is no owner, admin, setter, pause, upgrade or sweep, and no $owner or $token argument.

Permissions are exactly beforeSwap, afterSwap, beforeSwapReturnDelta, afterSwapReturnDelta (low address bits 0x00CC), all others false; the constructor calls Hooks.validateHookPermissions and the CREATE2 salt is mined for those bits.

The factory initializes the pool (currency0 native ETH, currency1 REFR, fee 3000, tickSpacing 60) and seeds one-sided REFR liquidity, so nothing in the hook may revert that initialize or that liquidity add (launch 138 was parked when a beforeInitialize gate reverted the factory), and the first buy lands in a pool that holds no ETH. All state is keyed by PoolId; a pool on this hook whose currency0 is not native ETH gets zero deltas and no other effect.

Every callback requires msg.sender == PoolManager.

Tests (Foundry, a real v4-core PoolManager deployed in the test, hook at a mined address): a launch rehearsal that initializes at the manifest price, seeds one-sided REFR liquidity like the factory and makes the first buy into the ETH-less pool; exact-in and exact-out in both directions; dust amounts; a pool whose currency0 is not ETH; direct callback calls from a non-PoolManager address revert; fuzzed sizes; and specifically: a 0.2% reward on all four swap modes; self, zero, hook and PoolManager referrers pay nothing; claim pays exactly once and a second claim pays zero; a referrer contract that rejects ETH blocks only its own claim; the sum of balances equals the hook's ETH claims under fuzzing.

An independent adversarial review (read-only) must attack: the referrer validity checks, fee sign and rounding, claim CEI and reentrancy through a receiving contract, and any path where the hook's ETH claims fall below the sum of balances. It reports each finding with the exact call sequence that triggers it.

Website: one static page (dist/index.html) that reads the hook's views and events and the pool price through Uniswap's Sepolia StateView 0xe1dd9c3fa50edb962e442f60dfbc432e24537e4c, with a buy/sell form that swaps through Uniswap's published Sepolia PoolSwapTest router 0x9b6b46e2c869aa39918db7f52f5557fe577b6eee (has code; manager() is the PoolManager above).

It shows a make-a-link box (?ref=address), a swap form that puts the ref from the URL in hookData, and the connected wallet's earnings, referral count and claim button.