Keel v2 contracts, part 2b: KeelV2Router, so every buyer pays and receives plain ETH in one transaction. Continue the Keel v2 project after part 2a. Same rules: immutable, no proxies, no sweep, Solidity 0.8.26, Cancun, via IR, bytecode_hash none, vendored deps, offline tests plus mainnet-fork tests that skip without a fork.

1. Purpose. Keel v2 pools pair a meme token with an allowlisted quote (ETH, USDC, IMD, wrapped tokens such as wSOL or wBTC). Buyers must never hold the quote. The router swaps ETH -> quote -> token on buy and token -> quote -> ETH on sell, atomically, inside one PoolManager unlock where possible.

2. Routes. The router owner (two-step ownership, separate from funds) sets one route per quote with setRoute(quote, route):

• NATIVE: the quote is ETH itself (address 0), so there is no first hop.
• V4: a Uniswap v4 PoolKey between native ETH and the quote (any fee, tick spacing and hooks; hooks must be address 0 or explicitly allowlisted by the owner; the hook allowlist starts empty and every change emits an event).
• V3: a Uniswap v3 pool address for WETH/quote. The router wraps and unwraps WETH itself and implements uniswapV3SwapCallback, accepting it only from that exact pool during an active swap. Routes can be replaced or removed by the owner. A route change never touches user funds; the router holds no balance between transactions.

3. buy(address token, uint256 minTokensOut, uint256 deadline) payable. Look up the Keel pool by token (hook.poolIdOf, factory.launchInfo for the PoolKey). Swap all msg.value ETH to the quote by the route (exact input), then swap the full quote output into the Keel pool (exact input, as the hook requires) with hookData = abi.encode(msg.sender) so the buyer gets heart credit. Send tokens to msg.sender. Revert if tokensOut < minTokensOut or block.timestamp > deadline. Settle input before take, as the part 1 README requires for quotes with no PoolManager inventory.

4. sell(address token, uint256 amountIn, uint256 minEthOut, uint256 deadline). Pull tokens from msg.sender only (transferFrom). Swap token -> quote in the Keel pool (exact input, hookData empty: sells never touch the heart), then quote -> ETH by the route, send ETH to msg.sender. Revert on minEthOut or deadline.

Events: Bought(address indexed buyer, address indexed token, uint256 ethIn, uint256 tokensOut) and Sold(address indexed seller, address indexed token, uint256 tokensIn, uint256 ethOut).

5. Quotes. quoteBuy(token, ethIn) and quoteSell(token, amountIn) for the site, implemented as revert-with-result simulations (callable via eth_call), covering both hops and the current hook fee. In the same block and state, quoteBuy and quoteSell must return exactly what buy and sell then deliver: test equality for every route type, not an approximation.

6. Safety. nonReentrant on buy and sell. No leftover tokens, quote or ETH stay in the router after a call: assert zero balance deltas at the end (dust from rounding goes to the user). Unlock callback accepts only PoolManager during the router's own active call. No arbitrary call targets. ETH sends use call and revert on failure.

7. Tests. Buy and sell for each route type (NATIVE, V4 with a mock v4 ETH/quote pool, V3 with a mock v3 pool), heart credit going to msg.sender and never to the router, spoof attempts (calling the Keel pool directly with someone else's address in hookData gives no credit), slippage and deadline reverts, fee-on-transfer and partial-fill rejection inherited from the hook, router balances zero after every call (including 1 wei buys, tiny sells that round to zero, which must revert, and the largest amounts a pool takes), route replacement, ownership. A quote with a transfer fee or rebasing balance is refused when its route is set or reverts the trade; it never leaves dust in the router. Fork tests against mainnet USDC and WETH pools when a fork URL is given.

8. Gas. Measure with forge snapshot and document in the README: buy and sell for each route type (NATIVE, V4, V3) at small and typical amounts, next to a direct single-pool swap of the same size. Report the router's overhead per route.

Deliver: source, tests, README section for part 2b, REVIEW.md update. Do not deploy.