diff --git a/solana/computer_test.go b/solana/computer_test.go
index 7de6c74..279ebeb 100644
--- a/solana/computer_test.go
+++ b/solana/computer_test.go
@@ -666,8 +666,23 @@ func testUserRequestSystemCall(ctx context.Context, require *require.Assertions,
 	id = uuid.Must(uuid.NewV4()).String()
 	extra = []byte{ConfirmFlagNonceAvailable}
 	extra = append(extra, uuid.Must(uuid.FromString(c.RequestId)).Bytes()...)
+	mainNonce, err := node.store.ReadNonceAccount(ctx, c.NonceAccount)
+	require.Nil(err)
+	nonceHash := solana.MustHashFromBase58(mainNonce.Hash)
+	extra = append(extra, nonceHash[:]...)
 	extra = attachSystemCall(extra, cid, raw)
 
+	for _, invalid := range [][]byte{extra[:1+uuid.Size], extra[:1+uuid.Size+31]} {
+		out := testBuildObserverRequest(node, uuid.Must(uuid.NewV4()).String(), OperationTypeConfirmNonce, invalid)
+		for _, node := range nodes {
+			testStep(ctx, require, node, out)
+			call, err := node.store.ReadSystemCallByRequestId(ctx, c.RequestId, common.RequestStateInitial)
+			require.Nil(err)
+			require.NotNil(call)
+			require.False(call.WithdrawalTraces.Valid)
+		}
+	}
+
 	out = testBuildObserverRequest(node, id, OperationTypeConfirmNonce, extra)
 	for _, node := range nodes {
 		testStep(ctx, require, node, out)
diff --git a/solana/mvm.go b/solana/mvm.go
index aae88ec..6c907e7 100644
--- a/solana/mvm.go
+++ b/solana/mvm.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"math/big"
 	"strings"
@@ -317,6 +318,9 @@ func (node *Node) processConfirmNonce(ctx context.Context, req *store.Request) (
 	switch call.State {
 	case common.RequestStateInitial:
 	case common.RequestStateFailed:
+		if !req.Restored {
+			return node.failRequest(ctx, req, "")
+		}
 		outputState = common.RequestStateDone
 	default:
 		return node.failRequest(ctx, req, "")
@@ -326,16 +330,47 @@ func (node *Node) processConfirmNonce(ctx context.Context, req *store.Request) (
 	if err != nil || user == nil {
 		panic(fmt.Errorf("store.ReadUser(%s) => %v %v", call.UserIdFromPublicPath(), user, err))
 	}
+	mix, err := bot.NewMixAddressFromString(user.MixAddress)
+	if err != nil {
+		panic(err)
+	}
 	os, _, err := node.GetSystemCallReferenceOutputs(ctx, call.UserIdFromPublicPath(), call.RequestHash, byte(outputState))
 	logger.Printf("node.GetSystemCallReferenceTxs(%s) => %v %v", req.MixinHash.String(), os, err)
 	if err != nil {
 		panic(err)
 	}
+	// Insufficient refund funds trigger compaction after the call is marked Failed.
+	// On replay, only rebuild the refund; do not revalidate or execute the main call.
+	if call.State == common.RequestStateFailed {
+		return node.refundAndFailRequest(ctx, req, mix.Members(), int(mix.Threshold), call, os)
+	}
+
 	switch flag {
 	case ConfirmFlagNonceAvailable:
+		// Available: call UUID, nonce hash, then the optional prepare call.
+		if len(extra) < uuid.Size+32 {
+			return node.failRequest(ctx, req, "")
+		}
+		nonceHash := solana.HashFromBytes(extra[uuid.Size : uuid.Size+32])
+		mainTx, err := solana.TransactionFromBase64(call.Raw)
+		if err != nil {
+			panic(err)
+		}
+		err = node.processTransactionWithAddressLookups(ctx, mainTx)
+		if err != nil {
+			if errors.Is(err, errInvalidAddressLookup) {
+				return node.refundAndFailRequest(ctx, req, mix.Members(), int(mix.Threshold), call, os)
+			}
+			panic(err)
+		}
+		err = verifySystemCallNonce(mainTx, call.NonceAccount, nonceHash, node.SolanaPayer())
+		logger.Printf("verifySystemCallNonce(%s) => %v", call.RequestId, err)
+		if err != nil {
+			return node.refundAndFailRequest(ctx, req, mix.Members(), int(mix.Threshold), call, os)
+		}
 		as := node.GetSystemCallRelatedAsset(ctx, os)
 		var sessions []*store.Session
-		prepare, tx, err := node.getSubSystemCallFromExtra(ctx, req, extra[16:])
+		prepare, tx, err := node.getSubSystemCallFromExtra(ctx, req, extra[uuid.Size+32:])
 		if err != nil {
 			return node.failRequest(ctx, req, "")
 		}
@@ -423,10 +458,6 @@ func (node *Node) processConfirmNonce(ctx context.Context, req *store.Request) (
 		}
 		return txs, ""
 	case ConfirmFlagNonceExpired:
-		mix, err := bot.NewMixAddressFromString(user.MixAddress)
-		if err != nil {
-			panic(err)
-		}
 		return node.refundAndFailRequest(ctx, req, mix.Members(), int(mix.Threshold), call, os)
 	default:
 		logger.Printf("invalid nonce confirm flag: %d", flag)
diff --git a/solana/observer.go b/solana/observer.go
index 38fc7bc..ba58ecf 100644
--- a/solana/observer.go
+++ b/solana/observer.go
@@ -644,6 +644,8 @@ func (node *Node) handleUnconfirmedCalls(ctx context.Context) error {
 		}
 
 		if failureReason == "" {
+			nonceHash := solana.MustHashFromBase58(nonce.Hash)
+			extra = append(extra, nonceHash[:]...)
 			err = node.OccupyNonceAccountByCall(ctx, nonce, call.RequestId)
 			if err != nil {
 				return err
diff --git a/solana/system_call.go b/solana/system_call.go
index e8d0933..6f533f7 100644
--- a/solana/system_call.go
+++ b/solana/system_call.go
@@ -19,6 +19,7 @@ import (
 	"github.com/MixinNetwork/safe/common"
 	"github.com/gagliardetto/solana-go"
 	computebudget "github.com/gagliardetto/solana-go/programs/compute-budget"
+	"github.com/gagliardetto/solana-go/programs/system"
 	"github.com/gofrs/uuid/v5"
 	"github.com/shopspring/decimal"
 )
@@ -554,6 +555,44 @@ func (node *Node) buildSystemCallFromBytes(ctx context.Context, req *store.Reque
 	return call, tx, nil
 }
 
+func verifySystemCallNonce(tx *solana.Transaction, nonceAccount string, nonceHash solana.Hash, authority solana.PublicKey) error {
+	if tx.Message.RecentBlockhash != nonceHash {
+		return fmt.Errorf("invalid system call nonce hash")
+	}
+	if len(tx.Message.Instructions) == 0 {
+		return fmt.Errorf("system call has no nonce advance")
+	}
+	ix := tx.Message.Instructions[0]
+	program, err := tx.Message.Program(ix.ProgramIDIndex)
+	if err != nil {
+		return err
+	}
+	if program != system.ProgramID {
+		return fmt.Errorf("invalid nonce advance program: %s", program)
+	}
+	accounts, err := ix.ResolveInstructionAccounts(&tx.Message)
+	if err != nil {
+		return err
+	}
+	if len(accounts) != 3 {
+		return fmt.Errorf("invalid nonce advance accounts: %d", len(accounts))
+	}
+	advance, err := solanaApp.DecodeNonceAdvance(accounts, ix.Data)
+	if err != nil {
+		return err
+	}
+	if advance.GetNonceAccount().PublicKey.String() != nonceAccount || !advance.GetNonceAccount().IsWritable {
+		return fmt.Errorf("invalid nonce account")
+	}
+	if advance.GetNonceAuthorityAccount().PublicKey != authority || !advance.GetNonceAuthorityAccount().IsSigner {
+		return fmt.Errorf("invalid nonce authority")
+	}
+	if advance.GetSysVarRecentBlockHashesPubkeyAccount().PublicKey != solana.SysVarRecentBlockHashesPubkey {
+		return fmt.Errorf("invalid nonce recent blockhashes sysvar")
+	}
+	return nil
+}
+
 func (node *Node) checkUserSystemCall(ctx context.Context, tx *solana.Transaction) error {
 	if common.CheckTestEnvironment(ctx) {
 		return nil