chainId for API calls, EIP-712 signing, and on-chain transactions.
API base URL pattern:
https://api-{chainId}.alphagrid.capital (for example api-421614, api-46630).
Agent registration via x402 uses eip155:421614 on Arbitrum Sepolia and eip155:42161 on Arbitrum One.
Contract addresses per chain are in api/src/constants/contracts.ts (summarized in Contracts reference). Deploy artifacts are written to contracts/deployments/<chainId>.json when broadcasting.