feat(protocol): allow block proposers to mint tokens on L2 if the block time > 12s [do not merge]

packages/protocol/contracts/team/ProposerFairmintPass.sol

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.24;
+
+import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+
+interface ITaikoL2 {
+    function parentTimestamp() external view returns (uint64);
+}
+
+/// @title ProposerFairmintPass
+/// @dev A token that can be fair-minted by block proposers (block.coinbase) if this block is
+/// proposed no early than 12 seconds after its parent block.
+/// This token then can be used for rewarding block proposers for Taiko L2's liveness.
+/// @custom:security-contact [email protected]
+/// TODO (dnaiel): we probably want to mint NFTs rather than ERC20 tokens.
+contract ProposerFairmintPass is ERC20 {
+    address public constant TAIKO_L2 = 0x1670080000000000000000000000000000010001;
+    uint256 public constant LAST_MINT_BLOCK = 50_000_000;
+    uint256 public constant MIN_BLOCK_TIME = 12 seconds;
+
+    uint64 public lastMintBlock;
+
+    error MINT_DISALLOWED();
+
+    constructor() ERC20("Taiko Proposer Fairmint Pass", "TPFP") { }
+
+    function mint() public {
+        uint256 amount = nextMintAmount();
+
+        if (
+            amount == 0 || block.number <= lastMintBlock
+                || block.timestamp < ITaikoL2(TAIKO_L2).parentTimestamp() + MIN_BLOCK_TIME
+        ) {
+            revert MINT_DISALLOWED();
+        }
+
+        lastMintBlock = uint64(block.number);
+        _mint(block.coinbase, amount);
+    }
+
+    function nextMintAmount() public view returns (uint256) {
+        if (block.number >= LAST_MINT_BLOCK) return 0;
+        return (4 ether) * (LAST_MINT_BLOCK - block.number) / LAST_MINT_BLOCK;
+    }
+}