itest: estimate on-chain fee with selected inputs

diff --git a/itest/list_on_test.go b/itest/list_on_test.go
index 02457d7..18732b1 100644
--- a/itest/list_on_test.go
+++ b/itest/list_on_test.go
@@ -759,6 +759,14 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "estimate fee",
 		TestFunc: testEstimateFee,
 	},
+	{
+		Name:     "estimate on chain fee with selected inputs",
+		TestFunc: testEstimateOnChainFeeWithSelectedInputs,
+	},
+	{
+		Name:     "estimate on chain fee auto selected inputs",
+		TestFunc: testEstimateOnChainFeeAutoSelectedInputs,
+	},
 }
 
 // appendPrefixed is used to add a prefix to each test name in the subtests
diff --git a/itest/lnd_estimate_on_chain_fee_test.go b/itest/lnd_estimate_on_chain_fee_test.go
new file mode 100644
index 0000000..7fd5d47
--- /dev/null
+++ b/itest/lnd_estimate_on_chain_fee_test.go
@@ -0,0 +1,232 @@
+package itest
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
+	"github.com/lightningnetwork/lnd/lntest"
+	"github.com/stretchr/testify/require"
+)
+
+// testEstimateOnChainFeeWithSelectedInputs tests that the EstimateFee RPC
+// with specific input selection produces an accurate fee estimate that matches
+// the actual fee when sending coins with the same inputs.
+func testEstimateOnChainFeeWithSelectedInputs(ht *lntest.HarnessTest) {
+	// Create a new node for this test.
+	alice := ht.NewNode("Alice", nil)
+
+	// Fund Alice with multiple UTXOs of different amounts to give us
+	// several inputs to choose from.
+	const (
+		utxo1Amount = btcutil.Amount(500_000)
+		utxo2Amount = btcutil.Amount(300_000)
+		utxo3Amount = btcutil.Amount(200_000)
+		targetConf  = 2
+	)
+
+	ht.FundCoins(utxo1Amount, alice)
+	ht.FundCoins(utxo2Amount, alice)
+	ht.FundCoins(utxo3Amount, alice)
+
+	// List Alice's UTXOs to get their outpoints.
+	utxosResp := alice.RPC.ListUnspent(&walletrpc.ListUnspentRequest{
+		MinConfs: 1,
+		MaxConfs: 1000,
+	})
+	require.GreaterOrEqual(ht, len(utxosResp.Utxos), 3,
+		"expected at least 3 UTXOs")
+
+	// Create a lookup map to find outpoints by amount.
+	utxoLookup := make(map[int64]*lnrpc.OutPoint)
+	for _, utxo := range utxosResp.Utxos {
+		utxoLookup[utxo.AmountSat] = utxo.Outpoint
+	}
+
+	// Select the first two UTXOs for our test.
+	selectedInputs := []*lnrpc.OutPoint{
+		utxoLookup[int64(utxo1Amount)],
+		utxoLookup[int64(utxo2Amount)],
+	}
+	require.NotNil(ht, selectedInputs[0], "first UTXO not found")
+	require.NotNil(ht, selectedInputs[1], "second UTXO not found")
+
+	// Generate a destination address for the transaction.
+	destAddrResp := alice.RPC.NewAddress(&lnrpc.NewAddressRequest{
+		Type: lnrpc.AddressType_WITNESS_PUBKEY_HASH,
+	})
+
+	// Amount to send (less than the sum of selected UTXOs to allow for
+	// fees and change).
+	const sendAmount = int64(400_000)
+
+	// Create an address-to-amount map for the transaction.
+	addrToAmount := map[string]int64{
+		destAddrResp.Address: sendAmount,
+	}
+
+	// Call EstimateFee with the selected inputs.
+	estimateReq := &lnrpc.EstimateFeeRequest{
+		AddrToAmount: addrToAmount,
+		TargetConf:   targetConf,
+		Inputs:       selectedInputs,
+	}
+	estimateResp, err := alice.RPC.LN.EstimateFee(ht.Context(), estimateReq)
+	require.NoError(ht, err, "EstimateFee failed")
+
+	ht.Logf("Fee estimate: %d sats, fee rate: %d sat/vbyte",
+		estimateResp.FeeSat, estimateResp.SatPerVbyte)
+
+	// Verify that the estimate response includes the inputs we specified.
+	require.Len(ht, estimateResp.Inputs, 2,
+		"expected 2 inputs in estimate response")
+
+	// Create a map of input outpoints from the estimate for an easy lookup.
+	estimateInputs := make(map[string]bool)
+	for _, input := range estimateResp.Inputs {
+		key := fmt.Sprintf("%s:%d", input.TxidStr, input.OutputIndex)
+		estimateInputs[key] = true
+	}
+
+	// Verify each selected outpoint is in the estimate.
+	for _, outpoint := range selectedInputs {
+		key := fmt.Sprintf("%s:%d", outpoint.TxidStr,
+			outpoint.OutputIndex)
+
+		require.True(ht, estimateInputs[key],
+			"outpoint %s not found in estimate inputs", key)
+	}
+
+	// Now actually send coins using the same parameters.
+	sendReq := &lnrpc.SendCoinsRequest{
+		Addr:       destAddrResp.Address,
+		Amount:     sendAmount,
+		TargetConf: targetConf,
+		Outpoints:  selectedInputs,
+	}
+	sendResp := alice.RPC.SendCoins(sendReq)
+	txid := sendResp.Txid
+
+	ht.Logf("Transaction sent with txid: %s", txid)
+
+	// Get the transaction details to extract the actual fee paid.
+	txDetails := alice.RPC.GetTransactions(
+		&lnrpc.GetTransactionsRequest{
+			StartHeight: 0,
+			EndHeight:   -1,
+		},
+	)
+
+	// Find our transaction in the list.
+	var actualFee int64
+	var found bool
+	for _, tx := range txDetails.Transactions {
+		if tx.TxHash == txid {
+			actualFee = tx.TotalFees
+			found = true
+			ht.Logf("Actual fee paid: %d sats", actualFee)
+
+			break
+		}
+	}
+	require.True(ht, found, "sent transaction not found")
+
+	require.EqualValues(
+		ht, estimateResp.FeeSat, actualFee, "fee estimate does not "+
+			"match actual fee",
+	)
+
+	// Mine the SendCoinsRequest.
+	ht.MineBlocksAndAssertNumTxes(1, 1)
+}
+
+// testEstimateOnChainFeeAutoSelectedInputs tests that the EstimateFee RPC
+// without input selection allows the wallet to auto-select inputs, and that
+// using those selected inputs in SendCoins produces a matching fee.
+func testEstimateOnChainFeeAutoSelectedInputs(ht *lntest.HarnessTest) {
+	// Create a new node for this test.
+	alice := ht.NewNode("Alice", nil)
+
+	// Fund Alice with multiple UTXOs.
+	const (
+		utxo1Amount = btcutil.Amount(500_000)
+		utxo2Amount = btcutil.Amount(300_000)
+		utxo3Amount = btcutil.Amount(200_000)
+		targetConf  = 2
+	)
+
+	ht.FundCoins(utxo1Amount, alice)
+	ht.FundCoins(utxo2Amount, alice)
+	ht.FundCoins(utxo3Amount, alice)
+
+	// Generate a destination address.
+	destAddrResp := alice.RPC.NewAddress(
+		&lnrpc.NewAddressRequest{
+			Type: lnrpc.AddressType_WITNESS_PUBKEY_HASH,
+		},
+	)
+
+	const sendAmount = int64(100_000)
+	addrToAmount := map[string]int64{
+		destAddrResp.Address: sendAmount,
+	}
+
+	// Estimate fee without specifying inputs (wallet auto-selects).
+	estimateReq := &lnrpc.EstimateFeeRequest{
+		AddrToAmount: addrToAmount,
+		TargetConf:   targetConf,
+	}
+	estimateResp, err := alice.RPC.LN.EstimateFee(ht.Context(), estimateReq)
+	require.NoError(ht, err, "EstimateFee failed")
+
+	ht.Logf("Fee estimate (auto-select): %d sats, "+
+		"fee rate: %d sat/vbyte, inputs selected: %d",
+		estimateResp.FeeSat, estimateResp.SatPerVbyte,
+		len(estimateResp.Inputs))
+
+	// The estimate should have selected some inputs.
+	require.NotEmpty(ht, estimateResp.Inputs,
+		"estimate should have selected inputs")
+
+	// Send using the inputs that were selected by the estimate.
+	sendReq := &lnrpc.SendCoinsRequest{
+		Addr:       destAddrResp.Address,
+		Amount:     sendAmount,
+		TargetConf: targetConf,
+		Outpoints:  estimateResp.Inputs,
+	}
+	sendResp := alice.RPC.SendCoins(sendReq)
+	txid := sendResp.Txid
+
+	ht.Logf("Transaction sent with txid: %s", txid)
+
+	// Get the actual fee.
+	txDetails := alice.RPC.GetTransactions(
+		&lnrpc.GetTransactionsRequest{
+			StartHeight: 0,
+			EndHeight:   -1,
+		},
+	)
+
+	var actualFee int64
+	var found bool
+	for _, tx := range txDetails.Transactions {
+		if tx.TxHash == txid {
+			actualFee = tx.TotalFees
+			found = true
+			ht.Logf("Actual fee paid: %d sats", actualFee)
+
+			break
+		}
+	}
+	require.True(ht, found, "sent transaction not found")
+
+	require.EqualValues(
+		ht, estimateResp.FeeSat, actualFee, "fee estimate does not "+
+			"match actual fee",
+	)
+
+	// Mine the SendCoinsRequest.
+	ht.MineBlocksAndAssertNumTxes(1, 1)
+}