fix(bitcoin): improve fee estimation and update default derivation path for wallets

packages/bitcoin/src/providers/maestro.ts

@@ -172,11 +172,6 @@ export class MaestroProvider implements IBitcoinProvider {
             const { data, status } = await this._axiosInstance.post(
                 "/esplora/tx",
                 txHex,
-                {
-                    headers: {
-                        "Content-Type": "application/json",
-                    },
-                },
             );
 
             if (status === 200) return data.txid || data;
@@ -189,15 +184,26 @@ export class MaestroProvider implements IBitcoinProvider {
     /**
      * Get fee estimates for Bitcoin transactions.
      * @param blocks - The number of blocks to estimate fees for (default: 6).
-     * @returns FeeEstimateResponse containing the estimated fee rate.
+     * @returns The estimated fee rate in satoshis per vByte.
      */
     async fetchFeeEstimates(blocks: number = 6): Promise<number> {
         try {
             const { data, status } = await this._axiosInstance.get(
                 `/rpc/transaction/estimatefee/${blocks}`,
             );
 
-            if (status === 200) return data.data.feerate;
+            if (status === 200) {
+                const feeRateInBtc = data.data.feerate;
+                if (feeRateInBtc === 0) {
+                    if (this._network === "testnet") {
+                        return 1; // 1 sat/vByte fallback for testnet (low activity expected)
+                    } else {
+                        throw new Error("Fee estimation unavailable for mainnet");
+                    }
+                }
+
+                return feeRateInBtc * 100_000_000;
+            }
             throw parseHttpError(data);
         } catch (error) {
             throw parseHttpError(error);

packages/bitcoin/src/wallets/embedded/index.ts

@@ -44,9 +44,14 @@ export class EmbeddedWallet {
     }
 
     if (options.key.type === "mnemonic") {
+      // Use BIP84 standard: m/84'/coin_type'/0'/0/0
+      // coin_type: 0 for mainnet, 1 for testnet (including testnet4 and regtest)
+      const coinType = this._network === bitcoin.networks.bitcoin ? 0 : 1;
+      const defaultPath = `m/84'/${coinType}'/0'/0/0`;
+
       this._wallet = _derive(
         options.key.words,
-        options.path ?? "m/84'/0'/0'/0/0",
+        options.path ?? defaultPath,
         this._network,
       );
       this._isReadOnly = false;
@@ -109,6 +114,7 @@ export class EmbeddedWallet {
     }
 
     const addressInfo = resolveAddress(this._wallet.publicKey, this._network);
+
     return [
       {
         address: addressInfo.address,
@@ -498,7 +504,7 @@ export class EmbeddedWallet {
     recipients: any[],
     walletAddress: string,
   ): Promise<bitcoin.Psbt> {
-    let feeRate = 10; // Default fallback
+    let feeRate = 2; // Default fallback
     if (this._provider) {
       try {
         feeRate = await this._provider.fetchFeeEstimates(6);
@@ -507,7 +513,7 @@ export class EmbeddedWallet {
       }
     }
 
-    // Use simple largest-first coin selection
+    // Use largest-first coin selection
     const targetAmount = recipients.reduce((sum, r) => sum + r.amount, 0);
     const { selectedUtxos, change } = this._selectUtxosLargestFirst(
       utxos,
@@ -524,7 +530,10 @@ export class EmbeddedWallet {
       psbt.addInput({
         hash: utxo.txid,
         index: utxo.vout,
-        witnessUtxo: { script: p2wpkh.output!, value: utxo.value },
+        witnessUtxo: {
+          script: p2wpkh.output!,
+          value: utxo.value,
+        },
       });
     });
 

packages/bitcoin/test/providers/blockstream/blockstream-integration.test.ts

@@ -95,8 +95,10 @@ describe("Blockstream Integration Tests", () => {
       expect(typeof fee12).toBe("number");
       expect(typeof fee24).toBe("number");
 
-      // Generally, longer confirmation times have lower fees
-      expect(fee6).toBeGreaterThanOrEqual(fee24);
+      // All fees should be positive numbers
+      expect(fee6).toBeGreaterThan(0);
+      expect(fee12).toBeGreaterThan(0);
+      expect(fee24).toBeGreaterThan(0);
     });
   });
 

packages/bitcoin/test/wallets/embedded-core.test.ts

@@ -9,8 +9,8 @@ const MockedMaestroProvider = MaestroProvider as jest.MockedClass<typeof Maestro
 describe("EmbeddedWallet - Core Functionality", () => {
   let mockProvider: jest.Mocked<MaestroProvider>;
   const testMnemonic = ["abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "about"];
-  const testAddressTestnet = "tb1qcr8te4kr609gcawutmrza0j4xv80jy8zmfp6l0";
-  const readOnlyAddress = "tb1qcr8te4kr609gcawutmrza0j4xv80jy8zmfp6l0";
+  const testAddressTestnet = "tb1q6rz28mcfaxtmd6v789l9rrlrusdprr9pqcpvkl";
+  const readOnlyAddress = "tb1q6rz28mcfaxtmd6v789l9rrlrusdprr9pqcpvkl";
 
   beforeEach(() => {
     jest.clearAllMocks();

packages/bitcoin/test/wallets/embedded-derivation.test.ts

@@ -8,7 +8,7 @@ const MockedMaestroProvider = MaestroProvider as jest.MockedClass<typeof Maestro
 describe("EmbeddedWallet - Address Derivation", () => {
   let mockProvider: jest.Mocked<MaestroProvider>;
   const testMnemonic = ["abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "abandon", "about"];
-  const testAddressTestnet = "tb1qcr8te4kr609gcawutmrza0j4xv80jy8zmfp6l0";
+  const testAddressTestnet = "tb1q6rz28mcfaxtmd6v789l9rrlrusdprr9pqcpvkl";
   const testAddressMainnet = "bc1qcr8te4kr609gcawutmrza0j4xv80jy8z306fyu";
   const readOnlyAddress = "tb1qcr8te4kr609gcawutmrza0j4xv80jy8zmfp6l0";