feat(frontend-dapp): optional Chain 2138 testnet in Wagmi config

- VITE_ENABLE_CHAIN2138 toggles chain list, supportedChainIds, and RPC map
- Aligns with docs/testnet runbook and pr-workspace chainlist metadata

Made-with: Cursor

frontend-dapp/src/config/networks.ts

@@ -17,6 +17,38 @@ const rpcUrl138 = import.meta.env.VITE_RPC_URL_138 || 'https://rpc-http-pub.d-bi
 const rpcUrl651940 = import.meta.env.VITE_RPC_URL_651940 || 'https://mainnet-rpc.alltra.global'
 const rpcUrl42793 = import.meta.env.VITE_RPC_URL_42793 || 'https://node.mainnet.etherlink.com'
 
+/** When true, testnet 2138 is included in Wagmi chains, RPC map, and supportedChainIds. */
+export const chain2138TestnetEnabled =
+  import.meta.env.VITE_ENABLE_CHAIN2138 === 'true' ||
+  import.meta.env.VITE_ENABLE_CHAIN2138 === '1'
+
+const rpcUrl2138 =
+  import.meta.env.VITE_RPC_URL_2138 || 'https://rpc.public-2138.defi-oracle.io'
+const explorerUrl2138 =
+  import.meta.env.VITE_EXPLORER_URL_2138 || 'https://public-2138.defi-oracle.io'
+
+/** Chain 2138 - Defi Oracle Meta Testnet (optional; enable with VITE_ENABLE_CHAIN2138) */
+export const chain2138Testnet = defineChain({
+  id: 2138,
+  name: 'Defi Oracle Meta Testnet',
+  network: 'chain2138-testnet',
+  nativeCurrency: {
+    decimals: 18,
+    name: 'testEther',
+    symbol: 'tETH',
+  },
+  rpcUrls: {
+    default: { http: [rpcUrl2138] },
+    public: { http: [rpcUrl2138] },
+  },
+  blockExplorers: {
+    default: {
+      name: 'Defi Oracle Meta Testnet Explorer',
+      url: explorerUrl2138,
+    },
+  },
+})
+
 /** Chain 138 - DeFi Oracle Meta Mainnet */
 export const chain138 = defineChain({
   id: 138,
@@ -128,8 +160,31 @@ export const gnosis = defineChain({
   blockExplorers: { default: { name: 'GnosisScan', url: 'https://gnosisscan.io' } },
 })
 
+const customChainsWithout2138 = [
+  chain138,
+  allMainnet,
+  etherlink,
+  bsc,
+  avalanche,
+  cronos,
+  gnosis,
+] as const
+
+const customChainsWith2138 = [
+  chain138,
+  chain2138Testnet,
+  allMainnet,
+  etherlink,
+  bsc,
+  avalanche,
+  cronos,
+  gnosis,
+] as const
+
 /** All custom chains (Viem Chain type) - for use with Wagmi/Viem */
-export const customChains = [chain138, allMainnet, etherlink, bsc, avalanche, cronos, gnosis] as const
+export const customChains = chain2138TestnetEnabled
+  ? customChainsWith2138
+  : customChainsWithout2138
 
 /** Standard L2s from wagmi/chains (Ethereum, Base, Arbitrum, Polygon, Optimism) */
 export const standardChains = [mainnet, base, arbitrum, polygon, optimism] as const
@@ -140,6 +195,7 @@ export const allNetworks = [...customChains, ...standardChains] as const
 /** Chain IDs we support (for CowSwap, Jumper, UI filters) - all deployed contract networks */
 export const supportedChainIds = [
   chain138.id,
+  ...(chain2138TestnetEnabled ? [chain2138Testnet.id] : []),
   allMainnet.id,
   etherlink.id,
   mainnet.id,
@@ -156,6 +212,7 @@ export const supportedChainIds = [
 /** Map chainId -> RPC URL for transports */
 export const chainRpcUrls: Record<number, string> = {
   [chain138.id]: rpcUrl138,
+  ...(chain2138TestnetEnabled ? { [chain2138Testnet.id]: rpcUrl2138 } : {}),
   [allMainnet.id]: rpcUrl651940,
   [etherlink.id]: rpcUrl42793,
   [bsc.id]: rpcUrlBsc,