Improve example configuration with environment-based RPC setup

[0xmusa1]

Problem

The current example scripts use hardcoded RPC URLs directly in the source code.

This makes local development and testing less flexible, especially when switching between environments such as:

• Base mainnet
• Base Sepolia
• Solana devnet
• custom RPC providers

Proposed Improvement

Add environment-based configuration support for the example scripts.

Possible improvements:

• add .env.example
• load RPC URLs from environment variables
• document expected environment variables

Benefit

This would improve developer experience and make the examples easier to configure across different environments.

[osr21]

Sharing the setup we use in a CCTP V2 bridge dApp that runs on Base Sepolia — this might be a useful reference for the .env.example approach.

We keep all chain configs (including RPC URLs) in a single chains.ts file with a primary RPC and a fallbacks array per chain. For Base Sepolia specifically:

// chains.ts
export const BASE_SEPOLIA: ChainConfig = {
  id: 84532,
  rpcUrl: import.meta.env.VITE_BASE_SEPOLIA_RPC ?? "https://sepolia.base.org",
  rpcFallbacks: [
    "https://base-sepolia.drpc.org",
    "https://base-sepolia-rpc.publicnode.com",
  ],
  // ...rest of config
};

// createRpcProvider.ts — tries primary, then each fallback in order
export async function createRpcProvider(chain: ChainConfig) {
  const urls = [chain.rpcUrl, ...chain.rpcFallbacks];
  for (const url of urls) {
    try {
      const provider = new ethers.JsonRpcProvider(url);
      await provider.getBlockNumber(); // liveness check
      return provider;
    } catch {
      // try next
    }
  }
  throw new Error(`All RPCs failed for ${chain.name}`);
}

The env var (VITE_BASE_SEPOLIA_RPC) lets developers swap in Alchemy/Infura/Ankr in production without changing code. The hardcoded fallbacks ensure the dApp still works out of the box with no .env file at all — useful for demos and contributors running the project for the first time.

Suggested .env.example entries:

# Optional — defaults to public endpoints if not set
VITE_BASE_SEPOLIA_RPC=https://sepolia.base.org
VITE_ETH_SEPOLIA_RPC=https://ethereum-sepolia-rpc.publicnode.com
VITE_AVAX_FUJI_RPC=https://api.avax-test.network/ext/bc/C/rpc

The pattern keeps the examples runnable for anyone cloning the repo while still being fully configurable for CI/production environments.