Add support for fast fill hyperliquid demo

Author: pedromcunha

demo/pages/sdk/actions/fastFill.tsx

@@ -103,7 +103,8 @@ const FastFillPage: NextPage = () => {
             tronWeb
           )
         }
-        // Note: Hyperliquid support can be added here following a similar pattern
+        // Note: Hyperliquid wallets are EVM-compatible and handled by the isEthereumWallet path above.
+        // The SDK automatically converts Hyperliquid transaction steps to signature steps (chain ID 1337).
 
         setAdaptedWallet(wallet)
       } catch (e: any) {

demo/utils/createFastFillWallet.ts

@@ -1,4 +1,4 @@
-import type { AdaptedWallet, Execute, TransactionStepItem } from '@relayprotocol/relay-sdk'
+import type { AdaptedWallet, Execute, SignatureStepItem, TransactionStepItem } from '@relayprotocol/relay-sdk'
 
 /**
  * Creates a fast-fill wallet adapter that wraps any AdaptedWallet
@@ -48,6 +48,19 @@ export const createFastFillWallet = (
 
   return {
     ...originalWallet,
+    handleSignMessageStep: async (
+      item: SignatureStepItem,
+      step: Execute['steps'][0]
+    ) => {
+      const signature = await originalWallet.handleSignMessageStep(item, step)
+
+      // Call fastFill proxy API after Hyperliquid signature deposit
+      if (step.requestId && step.id === ('hyperliquid-signature' as any)) {
+        await callFastFillAPI(step.requestId)
+      }
+
+      return signature
+    },
     handleSendTransactionStep: async (
       chainId: number,
       stepItem: TransactionStepItem,