docs: add Arc contract deployment notes

README.md

@@ -29,6 +29,7 @@ Arc is an open EVM-compatible layer 1 built on [Malachite](https://github.com/ci
 
 - 🚀 **[Execution](crates/node/README.md)** - Execution binary and configuration
 - 🗳️ **[Consensus](crates/malachite-app/README.md)** - Consensus binary and configuration
+- 🧱 **[Contract deployment](docs/deploying-contracts.md)** - Arc Testnet network, compiler, and verification settings
 - More: see Arc [developer docs](https://docs.arc.network/arc/concepts/welcome-to-arc) for guides, APIs, and specs
 
 ## Install and Run a Node

docs/deploying-contracts.md

@@ -0,0 +1,189 @@
+# Deploying Solidity contracts on Arc
+
+Arc is EVM-compatible, but developer tooling should be configured with the Arc
+network parameters explicitly. This page covers the settings that are most often
+needed when deploying contracts to Arc Testnet.
+
+## Arc Testnet network parameters
+
+```ts
+const arcTestnet = {
+  chainId: 5042002,
+  chainName: "Arc Testnet",
+  nativeCurrency: {
+    name: "USDC",
+    symbol: "USDC",
+    decimals: 18,
+  },
+  rpcUrls: ["https://rpc.testnet.arc.network"],
+  blockExplorerUrls: ["https://testnet.arcscan.app"],
+};
+```
+
+## Solidity compiler target
+
+When compiling contracts for Arc Testnet, target the Paris EVM unless your
+contract stack has confirmed support for newer EVM opcodes on the target Arc
+network.
+
+Solidity 0.8.20 and later can emit the Shanghai `PUSH0` opcode by default.
+Using `evmVersion: "paris"` avoids emitting `PUSH0` and keeps bytecode
+compatible with pre-Shanghai EVM targets.
+
+Hardhat example:
+
+```ts
+import type { HardhatUserConfig } from "hardhat/config";
+
+const config: HardhatUserConfig = {
+  solidity: {
+    version: "0.8.24",
+    settings: {
+      optimizer: { enabled: true, runs: 200 },
+      evmVersion: "paris",
+    },
+  },
+  networks: {
+    arcTestnet: {
+      url: "https://rpc.testnet.arc.network",
+      chainId: 5042002,
+      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : [],
+    },
+  },
+};
+
+export default config;
+```
+
+Foundry example:
+
+```toml
+# foundry.toml
+[profile.default]
+solc = "0.8.20"
+evm_version = "paris"
+optimizer = true
+optimizer_runs = 200
+# Uncomment only if your contract hits Solidity's stack-depth limit.
+# This can significantly increase compile time.
+# via_ir = true
+
+[rpc_endpoints]
+arc_testnet = "https://rpc.testnet.arc.network"
+```
+
+Deploy with:
+
+```bash
+forge script script/Deploy.s.sol:Deploy \
+  --rpc-url https://rpc.testnet.arc.network \
+  --private-key "$DEPLOYER_PRIVATE_KEY" \
+  --broadcast \
+  --config-path foundry.toml
+```
+
+The deployer wallet needs Arc Testnet USDC for gas. Testnet USDC is available
+from the [Circle faucet](https://faucet.circle.com).
+
+## Hardhat contract verification on Arcscan
+
+Arcscan is Blockscout-based. With `@nomicfoundation/hardhat-verify`, configure a
+custom chain that points to the Arcscan API endpoint.
+
+```ts
+import "@nomicfoundation/hardhat-verify";
+import type { HardhatUserConfig } from "hardhat/config";
+
+const config: HardhatUserConfig = {
+  networks: {
+    arcTestnet: {
+      url: "https://rpc.testnet.arc.network",
+      chainId: 5042002,
+      accounts: process.env.PRIVATE_KEY ? [process.env.PRIVATE_KEY] : [],
+    },
+  },
+  etherscan: {
+    apiKey: {
+      arcTestnet: "empty",
+    },
+    customChains: [
+      {
+        network: "arcTestnet",
+        chainId: 5042002,
+        urls: {
+          apiURL: "https://testnet.arcscan.app/api",
+          browserURL: "https://testnet.arcscan.app",
+        },
+      },
+    ],
+  },
+  sourcify: {
+    enabled: false,
+  },
+};
+
+export default config;
+```
+
+Then verify with constructor arguments as usual:
+
+```bash
+npx hardhat verify --network arcTestnet <contract-address> <constructor-args>
+```
+
+## Foundry contract verification on Arcscan
+
+Foundry can verify directly against Arcscan's Blockscout API:
+
+```bash
+forge verify-contract \
+  --verifier blockscout \
+  --verifier-url "https://testnet.arcscan.app/api/" \
+  --compiler-version 0.8.20 \
+  --evm-version paris \
+  --chain 5042002 \
+  <contract-address> src/<Contract>.sol:<Contract>
+```
+
+For constructor arguments, pass ABI-encoded args:
+
+```bash
+forge verify-contract \
+  --verifier blockscout \
+  --verifier-url "https://testnet.arcscan.app/api/" \
+  --compiler-version 0.8.20 \
+  --evm-version paris \
+  --chain 5042002 \
+  --constructor-args "$(cast abi-encode 'constructor(address,address)' <arg1> <arg2>)" \
+  <contract-address> src/<Contract>.sol:<Contract>
+```
+
+Notes:
+
+- Blockscout does not require a real Etherscan API key, but
+  `@nomicfoundation/hardhat-verify` still expects a non-empty string.
+- Replace `0.8.20` with the Solidity compiler version used for the deployment.
+  The verification compiler version must match the build exactly.
+- Keep the explorer URL as `https://testnet.arcscan.app` for wallet and dApp
+  transaction links.
+
+## Common Arc Testnet references
+
+| Item                 | Value                                        |
+| -------------------- | -------------------------------------------- |
+| Chain ID             | `5042002` (`0x4cef52`)                       |
+| RPC                  | `https://rpc.testnet.arc.network`            |
+| Explorer             | `https://testnet.arcscan.app`                |
+| Native USDC / gas    | `0x3600000000000000000000000000000000000000` |
+| EURC                 | `0x89B50855Aa3bE2F677cD6303Cec089B5F319D72a` |
+| CCTP domain          | `26`                                         |
+| TokenMessengerV2     | `0x8FE6B999Dc680CcFDD5Bf7EB0974218be2542DAA` |
+| MessageTransmitterV2 | `0xE737e5cEBEEBa77EFE34D4aa090756590b1CE275` |
+
+Native USDC uses 6 decimals through its ERC-20 interface for transfers,
+allowances, and balances, but native gas accounting such as `eth_getBalance`
+uses 18 decimals.
+
+For explorer readability, contracts can expose an `owner` view such as
+`address public owner`. Arcscan displays public variables in the contract view,
+which can help operators identify deployed instances.