fix: dispenser pallet derivation path and output schema

pallets/dispenser/src/lib.rs

@@ -290,9 +290,8 @@ pub mod pallet {
 			)?;
 
 			// Construct signing path used by SigNet.
-			let mut path = Vec::with_capacity(2 + requester.encoded_size() * 2);
-			path.extend_from_slice(b"0x");
-			path.extend_from_slice(hex::encode(requester.encode()).as_bytes());
+			// Fixed path so all requests derive the same MPC key (single funded address).
+			let path = b"dispenser".to_vec();
 
 			// CAIP-2 chain ID (e.g., "eip155:1" for Ethereum mainnet)
 			let caip2_id = alloc::format!("eip155:{}", tx.chain_id);
@@ -331,7 +330,8 @@ pub mod pallet {
 				Preservation::Expendable,
 			)?;
 
-			let output_deserialization_schema = Vec::<u8>::new();
+			let output_deserialization_schema =
+				serde_json::to_vec(&serde_json::json!([])).map_err(|_| Error::<T>::Serialization)?;
 			let respond_serialization_schema =
 				serde_json::to_vec(&serde_json::json!("bool")).map_err(|_| Error::<T>::Serialization)?;
 

scripts/dispenser-tests/dispenser.test.ts

@@ -31,6 +31,7 @@ describe('ERC20 Vault Integration', () => {
   let derivedPubKey: string
   let aliceHexPath: string
   let palletSS58: string
+  let onChainFaucetAddress: string
 
   beforeAll(async () => {
     await waitReady()
@@ -40,10 +41,12 @@ describe('ERC20 Vault Integration', () => {
     const feeAsset = (api.consts.ethDispenser.feeAsset as any).toNumber()
     const faucetAsset = (api.consts.ethDispenser.faucetAsset as any).toNumber()
 
+    onChainFaucetAddress = (api.consts.ethDispenser.faucetAddress as any).toHex()
+
     console.log(
       `feeAsset = ${feeAsset}`,
       `faucetAsset = ${faucetAsset}`,
-      `faucetAddress = ${api.consts.ethDispenser.faucetAddress.toString()}`,
+      `faucetAddress = ${onChainFaucetAddress}`,
     )
 
     const { keyring, alice: aliceAcc, bob } = createKeyringAndAccounts()
@@ -53,7 +56,7 @@ describe('ERC20 Vault Integration', () => {
     aliceHexPath = '0x' + u8aToHex(aliceAccountId).slice(2)
 
     await logAliceTokenBalances(api, alice, faucetAsset, feeAsset)
-    await ensureBobHasAssets(api, bob, faucetAsset)
+    await ensureBobHasAssets(api, alice, bob, faucetAsset)
 
     const palletFunding = await fundPalletAccounts(api, alice, faucetAsset)
     palletSS58 = palletFunding.palletSS58
@@ -67,7 +70,7 @@ describe('ERC20 Vault Integration', () => {
       ENV.SUBSTRATE_CHAIN_ID,
     )
 
-    const derived = deriveEthAddress()
+    const derived = deriveEthAddress(palletSS58)
     derivedEthAddress = derived.derivedEthAddress
     derivedPubKey = derived.derivedPubKey
 
@@ -118,7 +121,7 @@ describe('ERC20 Vault Integration', () => {
       maxPriorityFeePerGas: txParams.maxPriorityFeePerGas,
       maxFeePerGas: txParams.maxFeePerGas,
       gasLimit: txParams.gasLimit,
-      to: ENV.FAUCET_ADDRESS,
+      to: onChainFaucetAddress,
       value: 0,
       data,
     })
@@ -129,7 +132,7 @@ describe('ERC20 Vault Integration', () => {
       {
         caip2_id: `eip155:${ENV.EVM_CHAIN_ID}`,
         keyVersion: 0,
-        path: aliceHexPath,
+        path: 'dispenser',
         algo: 'ecdsa',
         dest: 'ethereum',
         params: '',

scripts/dispenser-tests/key-derivation.ts

@@ -6,13 +6,15 @@ export class KeyDerivation {
 
   static derivePublicKey(
     rootPublicKey: string,
+    predecessorId: string,
+    path: string,
     chainId: string
   ): string {
     const ec = new EC("secp256k1");
 
     const uncompressedRoot = rootPublicKey.slice(4);
 
-    const derivationPath = `${this.EPSILON_PREFIX},${chainId}`;
+    const derivationPath = `${this.EPSILON_PREFIX},${chainId},${predecessorId},${path}`;
     const hash = ethers.keccak256(ethers.toUtf8Bytes(derivationPath));
     const scalarHex = hash.slice(2);
 

scripts/dispenser-tests/utils.ts

@@ -231,6 +231,7 @@ export function createKeyringAndAccounts() {
 
 export async function ensureBobHasAssets(
   api: ApiPromise,
+  alice: any,
   bob: any,
   faucetAsset: number,
 ) {
@@ -240,21 +241,23 @@ export async function ensureBobHasAssets(
     bob.address,
   )) as any
 
-  const bobFaucetBalance = await getTokenFree(api, bob.address, faucetAsset)
-
-  if (bobBalance.free.toBigInt() < MIN_BOB_NATIVE_BALANCE) {
-    throw new Error(
-      `Bob has insufficient native balance: ${bobBalance.free.toBigInt()}. ` +
-        `Expected at least ${MIN_BOB_NATIVE_BALANCE}. Fund Bob via chopsticks config.`,
-    )
+  if (bobBalance.free.toBigInt() < 1000000000000n) {
+    console.log('Funding Bob from Alice...')
+    await new Promise<void>((resolve, reject) => {
+      api.tx.balances
+        .transferKeepAlive(bob.address, 100000000000000n)
+        .signAndSend(alice, (result: ISubmittableResult) => {
+          if (result.dispatchError) {
+            reject(result.dispatchError)
+          } else if (result.status.isInBlock) {
+            console.log("Bob's account funded!")
+            resolve()
+          }
+        })
+    })
   }
 
-  if (bobFaucetBalance < ethers.parseEther('1')) {
-    throw new Error(
-      `Bob has insufficient faucet asset (${faucetAsset}) balance: ${bobFaucetBalance}. ` +
-        `Fund Bob via chopsticks config.`,
-    )
-  }
+  const bobFaucetBalance = await getTokenFree(api, bob.address, faucetAsset)
 
   console.log(
     `Bob balances: native=${bobBalance.free.toBigInt()}, faucetAsset(${faucetAsset})=${bobFaucetBalance}`,
@@ -318,12 +321,14 @@ export async function fundPalletAccounts(
   return { palletSS58 }
 }
 
-export function deriveEthAddress(): {
+export function deriveEthAddress(palletSS58: string): {
   derivedPubKey: string
   derivedEthAddress: string
 } {
   const derivedPubKey = KeyDerivation.derivePublicKey(
     ENV.ROOT_PUBLIC_KEY,
+    palletSS58,
+    'dispenser',
     ENV.SUBSTRATE_CHAIN_ID,
   )