Blocks

Blocks are optional rules a creator switches on at launch. They are stored in the hook per pool, validated once by Blocks.validate, and can never be changed, added or removed afterwards. Four exist: Anti-Snipe, Auto Burn, Nth-buy Pot and Halt Guard. A bit mask selects them; each has a handful of parameters with hard ranges.

The config

struct Config {
    uint8   mask;              // ANTI_SNIPE = 1, AUTO_BURN = 2, NTH_BUY_POT = 4, HALT_GUARD = 8
    uint32  snipeWindowBlocks; // AntiSnipe
    uint16  snipeMaxBuyBps;    // AntiSnipe
    uint16  snipeTaxBps;       // AntiSnipe
    uint16  burnBps;           // AutoBurn
    uint16  potBps;            // NthBuyPot
    uint32  potN;              // NthBuyPot
    uint128 potMinBuy;         // NthBuyPot, raw quote units
    uint32  haltMaxStaleness;  // HaltGuard, seconds
}

validate rejects unknown mask bits and, for every block, requires its fields to be inside the range when the block is on and exactly zero when it is off. The web app mirrors the same rules in validate() and zeroes disabled fields in normalize() before sending the transaction, so a config that passes in the browser passes on chain.

Execution order on a buy

Blocks only act on buys. Sells are never capped, taxed, counted or refused. The order is fixed in _beforeSwap and _afterSwap:

Anti-Snipe

For snipeWindowBlocks blocks after launch, two things happen on every buy: the cumulative quote bought in the current block must stay under a cap, and an extra fee is charged and credited to the creator.

The cap is cumulative per block and per pool, not per address: boughtInBlock[id][block.number] + quoteIn must not exceed snipeCapQuote, otherwise the buy reverts OverSnipeCap. It never trims the order down. Because the cap is expressed as a share of the opening FDV in quote units, it means the same thing for a USDC pool and a cirBTC pool. Arc's blocks are about 0.5 s apart, so a window of 100 blocks is under a minute; size the window in seconds first and divide by two.

Auto Burn

After every buy, burnBps of the token output is taken from the PoolManager and burned through LaunchToken.burn, reducing totalSupply. The buyer receives tokensOut − burned; the event already reflects that.

Auto Burn does not touch sells and does not change the price directly; it shrinks the supply that exists outside the pool. The burn is an ERC-20 supply reduction inside LaunchToken, never a native transfer, so Arc's rule against sending value to address(0) does not apply. The indexer keeps pool.tokensBurned.

Nth-buy Pot

A share of every buy's quote input goes into a pot. A public counter advances once per block for buys that qualify; every potN-th advance wins the whole pot. Winnings are claim-backed: they move to potOwed[id][winner] and the winner (only the winner) calls claimPot(id, to).

Three rules keep the pot honest:

• One advance per block. potLastBlock[id] stops a single transaction, or a bundle, from advancing the counter several times in one block to land on N.
• The recipient wins. The counter records the swap's recipient as reported by a trusted router (hookData), or tx.origin otherwise. A zero recipient never qualifies.
• The counter is public. Anyone can read potCount and pot on chain or in the indexer. Whoever makes the Nth qualifying buy wins; there is no randomness and no hidden state. That also means Arc's PREVRANDAO, which is always 0, is never consulted.

Halt Guard

Refuses buys while the quote's oracle is unusable: feed stale beyond haltMaxStaleness, non-positive answer, or the quote token reporting paused(). Sells always pass, so holders can exit during a halt. It applies equally to USDC and cirBTC pools: for USDC it is mostly a Circle-pause guard, for cirBTC it also catches a stalled BTC / USD feed.

The read is registry.quoteHalted(quote, haltMaxStaleness), detailed in Quotes and the oracle.

Gas and drag

The Builder shows an estimated gas figure (base 240k plus roughly 45k for Halt Guard, 20k for Anti-Snipe, 45k for the pot and 35k for Auto Burn) and a nominal buy drag of 80 bps plus the pot share, plus the snipe tax while the window is open. At Arc's 20 to 100 gwei base fee (paid in USDC) a fully loaded buy costs well under $0.05 in gas. Both figures are client-side estimates; the chain is the truth.

read the code

• contracts/src/blocks/Blocks.sol Config, limits, validate()
• contracts/src/HookarcHook.sol _beforeSwap (HaltGuard, AntiSnipe, pot), _autoBurn, claimPot
• contracts/test/Blocks.t.sol validation and each block in isolation
• contracts/test/invariant/BlocksInvariant.t.sol burn only shrinks supply; pot counter monotone
• web/lib/blocks.ts the browser mirror of validate() and normalize()