A Uniswap v4 hook that prices the hours the stock market is closed, so LPs on tokenized stocks get paid for the weekend gap.
Tokenized stocks trade 24/7 onchain, but the real market doesn't. When NYSE is closed the issuer can't mint or redeem and there is no live price to arbitrage against, so LPs carry the whole overnight and weekend gap for free. On 29-31 Aug 2026 the HIMS wrapper on Robinhood Chain printed $61.15 against a $28.84 close (+112%), and zero of the chain's top pools used a dynamic fee.
Gapguard is a Uniswap v4 hook that prices the closed market. It computes the NYSE session onchain (DST, holidays, early closes, no oracle or keeper). While the market is open, swaps pay the base fee and a time-weighted 'last close' anchor follows the price. While it is closed, every swap pays a gap-risk surcharge, and swaps that push price away from the last close pay a drift surcharge that grows with the distance; flow that restores the peg stays cheap. One swap can move price at most ~1% while closed, so repricing can't dodge the fee by splitting.
Everything is an LP fee, so it accrues to the liquidity that actually took the risk. In a replay of the HIMS weekend, LPs earn 12.7x more. The hook keeps 15% of the surcharge only. No owner, no admin, no upgrade; reviewed adversarially three times; source verified on Sourcify.
Built entirely during the buildathon: the GapguardHook contract, the onchain NYSE calendar library (MarketClock), 39 Foundry tests incl. a HIMS weekend replay, three adversarial security reviews with every finding fixed and pinned by a test, a mainnet deployment on Robinhood Chain with a live demo pool, and the demo site with live pool reads and one-click fee collection.
