fix: gate Fast Transfer by source-chain support

src/app/page.tsx

@@ -36,6 +36,7 @@ import {
   SupportedChainId,
   SUPPORTED_CHAINS,
   CHAIN_CONFIGS,
+  supportsFastTransfer,
 } from "@/lib/chains";
 import { ProgressSteps } from "@/components/progress-step";
 import { TransferLog } from "@/components/transfer-log";
@@ -69,7 +70,9 @@ export default function Home() {
   const [elapsedSeconds, setElapsedSeconds] = useState(0);
   const [isTransferring, setIsTransferring] = useState(false);
   const [showFinalTime, setShowFinalTime] = useState(false);
-  const [transferType, setTransferType] = useState<"fast" | "standard">("fast");
+  const [transferType, setTransferType] = useState<"fast" | "standard">(
+    "standard",
+  );
   const [balance, setBalance] = useState("0");
   const [wallets, setWallets] = useState<WalletConnections>({
     evm: null,
@@ -90,6 +93,7 @@ export default function Home() {
 
   const sourceEcosystem = CHAIN_CONFIGS[sourceChain].ecosystem;
   const destinationEcosystem = CHAIN_CONFIGS[destinationChain].ecosystem;
+  const fastTransferSupported = supportsFastTransfer(sourceChain);
   const needsEvmWallet =
     sourceEcosystem === "evm" || destinationEcosystem === "evm";
   const needsSolanaWallet =
@@ -129,6 +133,14 @@ export default function Home() {
     setElapsedSeconds(0);
   };
 
+  const handleSourceChainChange = (value: string) => {
+    const chainId = Number(value) as SupportedChainId;
+    setSourceChain(chainId);
+    if (!supportsFastTransfer(chainId)) {
+      setTransferType("standard");
+    }
+  };
+
   const handleEvmWalletClick = async () => {
     if (wallets.evm) {
       setWallets((current) => ({ ...current, evm: null }));
@@ -367,9 +379,12 @@ export default function Home() {
             <TransferTypeSelector
               value={transferType}
               onChange={setTransferType}
+              fastDisabled={!fastTransferSupported}
             />
             <p className="text-sm text-muted-foreground">
-              {transferType === "fast"
+              {!fastTransferSupported
+                ? `Fast Transfer is not available from ${CHAIN_CONFIGS[sourceChain].name}.`
+                : transferType === "fast"
                 ? "Faster transfers with lower finality threshold (1000 blocks)"
                 : "Standard transfers with higher finality (2000 blocks)"}
             </p>
@@ -379,7 +394,7 @@ export default function Home() {
               <Label>Source Chain</Label>
               <Select
                 value={String(sourceChain)}
-                onValueChange={(value) => setSourceChain(Number(value))}
+                onValueChange={handleSourceChainChange}
               >
                 <SelectTrigger>
                   <SelectValue placeholder="Select source chain" />

src/components/transfer-type.tsx

@@ -23,16 +23,20 @@ import { Tabs, TabsList, TabsTrigger } from "@/components/ui/tabs";
 export function TransferTypeSelector({
   value,
   onChange,
+  fastDisabled = false,
 }: {
   value: "fast" | "standard";
   onChange: (value: "fast" | "standard") => void;
+  fastDisabled?: boolean;
 }) {
   return (
     <Tabs value={value} onValueChange={(v) => onChange(v as "fast" | "standard")}>
       <TabsList className="grid w-full grid-cols-2">
-        <TabsTrigger value="fast">Fast Transfer</TabsTrigger>
+        <TabsTrigger value="fast" disabled={fastDisabled}>
+          Fast Transfer
+        </TabsTrigger>
         <TabsTrigger value="standard">Standard Transfer</TabsTrigger>
       </TabsList>
     </Tabs>
   );
-}
+}

src/hooks/use-cross-chain-transfer.ts

@@ -46,6 +46,7 @@ import {
   CHAIN_CONFIGS,
   SOLANA_RPC_ENDPOINT,
   IRIS_API_URL,
+  supportsFastTransfer,
 } from "@/lib/chains";
 import {
   ensureEvmChain,
@@ -72,6 +73,7 @@ interface AttestationResponse {
 }
 
 interface FastTransferFeeResponse {
+  finalityThreshold: number;
   minimumFee: number | string;
 }
 
@@ -111,6 +113,15 @@ export function useCrossChainTransfer() {
       const destinationEcosystem =
         CHAIN_CONFIGS[destinationChainId as SupportedChainId].ecosystem;
 
+      if (
+        transferType === "fast" &&
+        !supportsFastTransfer(sourceChainId as SupportedChainId)
+      ) {
+        throw new Error(
+          `Fast Transfer is not available from ${CHAIN_CONFIGS[sourceChainId as SupportedChainId].name}.`,
+        );
+      }
+
       const sourceClient = getClients(sourceChainId, wallets);
       const destinationClient = getClients(destinationChainId, wallets);
       const defaultDestination = getDestinationAddress(
@@ -1024,9 +1035,12 @@ export function useCrossChainTransfer() {
     }
 
     const feePayload = (await response.json()) as FastTransferFeeResponse[];
-    const feeEntry = feePayload[0];
+    const feeEntry = feePayload.find(
+      ({ finalityThreshold }) =>
+        finalityThreshold === FAST_FINALITY_THRESHOLD,
+    );
     if (!feeEntry) {
-      throw new Error("No fee returned for this route");
+      throw new Error("No Fast Transfer fee returned for this route");
     }
 
     const minimumFeeBpsHundredths = parseFeeBps(feeEntry.minimumFee);

src/lib/chains.ts

@@ -385,6 +385,26 @@ export const CHAIN_CONFIGS: Record<SupportedChainId, ChainConfig> = {
 export const SUPPORTED_CHAINS = (Object.keys(CHAIN_CONFIGS).map(Number) as SupportedChainId[])
   .sort((a, b) => CHAIN_CONFIGS[a].name.localeCompare(CHAIN_CONFIGS[b].name));
 
+const FAST_TRANSFER_SOURCE_CHAINS = new Set<SupportedChainId>([
+  SupportedChainId.ARBITRUM_SEPOLIA,
+  SupportedChainId.BASE_SEPOLIA,
+  SupportedChainId.CODEX_TESTNET,
+  SupportedChainId.EDGE_TESTNET,
+  SupportedChainId.ETH_SEPOLIA,
+  SupportedChainId.INK_SEPOLIA,
+  SupportedChainId.LINEA_SEPOLIA,
+  SupportedChainId.MORPH_HOODI,
+  SupportedChainId.OPTIMISM_SEPOLIA,
+  SupportedChainId.PLUME_SEPOLIA,
+  SupportedChainId.SOLANA_DEVNET,
+  SupportedChainId.UNICHAIN_SEPOLIA,
+  SupportedChainId.WORLDCHAIN_SEPOLIA,
+]);
+
+export function supportsFastTransfer(chainId: SupportedChainId) {
+  return FAST_TRANSFER_SOURCE_CHAINS.has(chainId);
+}
+
 export const SOLANA_RPC_ENDPOINT = "https://api.devnet.solana.com";
 
 export const IRIS_API_URL = "https://iris-api-sandbox.circle.com";