payments/migration1: add the payments mig code

diff --git a/payments/db/migration1/migration_validation.go b/payments/db/migration1/migration_validation.go
new file mode 100644
index 0000000..e97c3db
--- /dev/null
+++ b/payments/db/migration1/migration_validation.go
@@ -0,0 +1,555 @@
+package migration1
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"fmt"
+	"reflect"
+	"sort"
+	"time"
+
+	"github.com/davecgh/go-spew/spew"
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/payments/db/migration1/sqlc"
+	"github.com/lightningnetwork/lnd/record"
+	"github.com/pmezard/go-difflib/difflib"
+)
+
+// migratedPaymentRef is a reference to a migrated payment.
+type migratedPaymentRef struct {
+	Hash      lntypes.Hash
+	PaymentID int64
+}
+
+// validateMigratedPaymentBatch performs a structural validation pass by
+// comparing key fields (hash, amount, fail reason, HTLC count) of KV payments
+// with their SQL counterparts. If a structural mismatch is detected, a full
+// deep comparison is performed to produce a detailed diff for debugging.
+func validateMigratedPaymentBatch(ctx context.Context,
+	kvBackend kvdb.Backend, sqlDB SQLQueries,
+	cfg *SQLStoreConfig, batch []migratedPaymentRef) error {
+
+	if len(batch) == 0 {
+		return nil
+	}
+
+	if cfg == nil || cfg.QueryCfg == nil {
+		return fmt.Errorf("missing SQL store config for validation")
+	}
+
+	paymentIDs := make([]int64, 0, len(batch))
+	for _, item := range batch {
+		paymentIDs = append(paymentIDs, item.PaymentID)
+	}
+
+	rows, err := sqlDB.FetchPaymentsByIDsMig(ctx, paymentIDs)
+	if err != nil {
+		return fmt.Errorf("fetch SQL payments: %w", err)
+	}
+	if len(rows) != len(paymentIDs) {
+		return fmt.Errorf("SQL payment batch mismatch: got=%d want=%d",
+			len(rows), len(paymentIDs))
+	}
+
+	// Perform the structural check by comparing key fields from the KV
+	// store with the SQL store.
+	err = kvBackend.View(func(kvTx kvdb.RTx) error {
+		paymentsBucket := kvTx.ReadBucket(paymentsRootBucket)
+		if paymentsBucket == nil {
+			return fmt.Errorf("no payments bucket")
+		}
+
+		for _, row := range rows {
+			hash := row.PaymentIdentifier
+			var paymentHash lntypes.Hash
+			copy(paymentHash[:], hash)
+
+			paymentBucket := paymentsBucket.NestedReadBucket(hash)
+			if paymentBucket == nil {
+				return fmt.Errorf("missing payment bucket %x",
+					hash[:8])
+			}
+
+			kvPayment, err := fetchPayment(paymentBucket)
+			if err != nil {
+				return fmt.Errorf("fetch KV payment %x: %w",
+					hash[:8], err)
+			}
+
+			err = structuralCompare(kvPayment, row)
+			if err != nil {
+				// On structural mismatch, perform a deep
+				// comparison to produce a detailed diff.
+				deepErr := deepComparePayment(
+					ctx, cfg, sqlDB, row.ID,
+					paymentHash, kvPayment,
+				)
+				if deepErr != nil {
+					return deepErr
+				}
+
+				// If deep comparison passes but structural
+				// failed, report the structural error as it
+				// indicates an unexpected inconsistency.
+				return err
+			}
+
+			err = compareDuplicatePayments(
+				ctx, paymentBucket, sqlDB, row.ID,
+				paymentHash,
+			)
+			if err != nil {
+				return err
+			}
+		}
+
+		return nil
+	}, func() {})
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// structuralCompare performs a fast structural comparison between a KV payment
+// and a SQL payment row, checking key fields: payment identifier, amount,
+// failure reason, and HTLC attempt count.
+func structuralCompare(kvPayment *MPPayment,
+	sqlRow sqlc.FetchPaymentsByIDsMigRow) error {
+
+	// Compare payment identifier.
+	kvHash := kvPayment.Info.PaymentIdentifier[:]
+	if !bytes.Equal(kvHash, sqlRow.PaymentIdentifier) {
+		return fmt.Errorf("payment identifier mismatch: kv=%x sql=%x",
+			kvHash[:8], sqlRow.PaymentIdentifier[:8])
+	}
+
+	// Compare amount.
+	kvAmount := int64(kvPayment.Info.Value)
+	if kvAmount != sqlRow.AmountMsat {
+		return fmt.Errorf("amount mismatch for %x: kv=%d sql=%d",
+			sqlRow.PaymentIdentifier[:8], kvAmount,
+			sqlRow.AmountMsat)
+	}
+
+	// Compare failure reason.
+	var kvFailReason sql.NullInt32
+	if kvPayment.FailureReason != nil {
+		kvFailReason = sql.NullInt32{
+			Int32: int32(*kvPayment.FailureReason),
+			Valid: true,
+		}
+	}
+	if kvFailReason != sqlRow.FailReason {
+		return fmt.Errorf("fail reason mismatch for %x: kv=%v sql=%v",
+			sqlRow.PaymentIdentifier[:8], kvFailReason,
+			sqlRow.FailReason)
+	}
+
+	// Compare HTLC attempt count.
+	kvHTLCCount := int64(len(kvPayment.HTLCs))
+	if kvHTLCCount != sqlRow.HtlcAttemptCount {
+		return fmt.Errorf("HTLC count mismatch for %x: kv=%d sql=%d",
+			sqlRow.PaymentIdentifier[:8], kvHTLCCount,
+			sqlRow.HtlcAttemptCount)
+	}
+
+	return nil
+}
+
+// deepComparePayment performs a full deep comparison between a KV payment and
+// its SQL counterpart, producing a detailed diff on mismatch.
+func deepComparePayment(ctx context.Context, cfg *SQLStoreConfig,
+	sqlDB SQLQueries, paymentID int64, paymentHash lntypes.Hash,
+	kvPayment *MPPayment) error {
+
+	batchData, err := batchLoadPaymentDetailsData(
+		ctx, cfg.QueryCfg, sqlDB, []int64{paymentID},
+	)
+	if err != nil {
+		return fmt.Errorf("load payment data for deep compare %x: %w",
+			paymentHash[:8], err)
+	}
+
+	byIDRows, err := sqlDB.FetchPaymentsByIDs(ctx, []int64{paymentID})
+	if err != nil {
+		return fmt.Errorf("fetch payment by ID for deep compare "+
+			"%x: %w", paymentHash[:8], err)
+	}
+	if len(byIDRows) != 1 {
+		return fmt.Errorf("expected 1 payment for deep compare, "+
+			"got %d", len(byIDRows))
+	}
+
+	sqlPayment, err := buildPaymentFromBatchData(byIDRows[0], batchData)
+	if err != nil {
+		return fmt.Errorf("build SQL payment %x: %w",
+			paymentHash[:8], err)
+	}
+
+	normalizePaymentForCompare(kvPayment)
+	normalizePaymentForCompare(sqlPayment)
+
+	if !reflect.DeepEqual(kvPayment, sqlPayment) {
+		dumpCfg := spew.ConfigState{
+			DisablePointerAddresses: true,
+			DisableCapacities:       true,
+			DisableMethods:          true,
+			SortKeys:                true,
+		}
+		diff := difflib.UnifiedDiff{
+			A: difflib.SplitLines(
+				dumpCfg.Sdump(kvPayment),
+			),
+			B: difflib.SplitLines(
+				dumpCfg.Sdump(sqlPayment),
+			),
+			FromFile: "kv",
+			ToFile:   "sql",
+			Context:  3,
+		}
+		diffText, _ := difflib.GetUnifiedDiffString(diff)
+
+		return fmt.Errorf("payment mismatch %x\n%s",
+			paymentHash[:8], diffText)
+	}
+
+	return nil
+}
+
+// normalizePaymentForCompare normalizes fields that are expected to differ
+// between KV and SQL representations before deep comparison.
+func normalizePaymentForCompare(payment *MPPayment) {
+	if payment == nil {
+		return
+	}
+
+	// SequenceNum will not be equal because the kv db can have already
+	// payments deleted during its lifetime.
+	payment.SequenceNum = 0
+
+	// We normalize timestamps before deep-comparing KV vs SQL objects.
+	//
+	// - **Microseconds**: SQL backends typically persist timestamps at
+	//   microsecond precision (e.g. Postgres), while KV (Go `time.Time`)
+	//   can contain nanoseconds. Truncating avoids false mismatches caused
+	//   solely by differing storage precision.
+	//
+	// - **Local timezone**: when reading from SQL, timestamps are typically
+	//   materialized in the local timezone by the SQL layer (and/or
+	//   converters). Converting both sides to `time.Local` ensures the
+	//   comparison is consistent across KV and SQL representations.
+	trunc := func(t time.Time) time.Time {
+		if t.IsZero() {
+			return t
+		}
+
+		return time.Unix(0, t.UnixNano()).
+			In(time.Local).
+			Truncate(time.Microsecond)
+	}
+
+	// Normalize PaymentCreationInfo fields.
+	if payment.Info != nil {
+		payment.Info.CreationTime = trunc(
+			payment.Info.CreationTime,
+		)
+		if len(payment.Info.PaymentRequest) == 0 {
+			payment.Info.PaymentRequest = []byte{}
+		}
+		if len(payment.Info.FirstHopCustomRecords) == 0 {
+			payment.Info.FirstHopCustomRecords = lnwire.
+				CustomRecords{}
+		}
+	}
+
+	// Normalize HTLCAttemptInfo so nil is converted to an empty slice.
+	if len(payment.HTLCs) == 0 {
+		payment.HTLCs = []HTLCAttempt{}
+	}
+
+	// Normalize HTLC attempt ordering; SQL/KV may return attempts
+	// in different orders.
+	sort.SliceStable(payment.HTLCs, func(i, j int) bool {
+		return payment.HTLCs[i].AttemptID < payment.HTLCs[j].AttemptID
+	})
+
+	// Normalize HTLCAttemptInfo fields.
+	for i := range payment.HTLCs {
+		htlc := &payment.HTLCs[i]
+
+		htlc.AttemptTime = trunc(htlc.AttemptTime)
+		if htlc.Settle != nil {
+			htlc.Settle.SettleTime = trunc(
+				htlc.Settle.SettleTime,
+			)
+		}
+		if htlc.Failure != nil {
+			htlc.Failure.FailTime = trunc(
+				htlc.Failure.FailTime,
+			)
+		}
+
+		// Clear cached fields not persisted in storage.
+		htlc.onionBlob = [1366]byte{}
+		htlc.circuit = nil
+		htlc.cachedSessionKey = nil
+
+		if len(htlc.Route.FirstHopWireCustomRecords) == 0 {
+			htlc.Route.FirstHopWireCustomRecords =
+				lnwire.CustomRecords{}
+		}
+
+		for j := range htlc.Route.Hops {
+			if len(htlc.Route.Hops[j].CustomRecords) == 0 {
+				htlc.Route.Hops[j].CustomRecords =
+					record.CustomSet{}
+			}
+		}
+	}
+}
+
+// duplicateRecord is a record that represents a duplicate payment.
+type duplicateRecord struct {
+	AmountMsat     int64
+	CreatedAt      time.Time
+	FailReason     sql.NullInt32
+	SettlePreimage []byte
+	SettleTime     sql.NullTime
+}
+
+// compareDuplicatePayments validates migrated duplicate rows against KV data.
+func compareDuplicatePayments(ctx context.Context, paymentBucket kvdb.RBucket,
+	sqlDB SQLQueries, paymentID int64, hash lntypes.Hash) error {
+
+	// Fetch the duplicate payments from the KV store.
+	kvDuplicates, err := fetchDuplicateRecords(paymentBucket)
+	if err != nil {
+		return fmt.Errorf("fetch KV duplicates %x: %w",
+			hash[:8], err)
+	}
+
+	// Fetch the duplicate payments from the SQL store.
+	sqlDuplicates, err := sqlDB.FetchPaymentDuplicates(ctx, paymentID)
+	if err != nil {
+		return fmt.Errorf("fetch SQL duplicates %x: %w",
+			hash[:8], err)
+	}
+
+	if len(kvDuplicates) != len(sqlDuplicates) {
+		return fmt.Errorf("duplicate count mismatch %x: kv=%d "+
+			"sql=%d", hash[:8], len(kvDuplicates),
+			len(sqlDuplicates))
+	}
+
+	kvNormalized := normalizeDuplicateRecords(kvDuplicates)
+	sqlNormalized := normalizeDuplicateRecords(
+		dbDuplicatesToDuplicateRecords(sqlDuplicates),
+	)
+
+	sortDuplicates(kvNormalized)
+	sortDuplicates(sqlNormalized)
+
+	if !reflect.DeepEqual(kvNormalized, sqlNormalized) {
+		dumpCfg := spew.ConfigState{
+			DisablePointerAddresses: true,
+			DisableCapacities:       true,
+			DisableMethods:          true,
+			SortKeys:                true,
+		}
+		diff := difflib.UnifiedDiff{
+			A: difflib.SplitLines(
+				dumpCfg.Sdump(kvNormalized),
+			),
+			B: difflib.SplitLines(
+				dumpCfg.Sdump(sqlNormalized),
+			),
+			FromFile: "kv",
+			ToFile:   "sql",
+			Context:  3,
+		}
+		diffText, _ := difflib.GetUnifiedDiffString(diff)
+
+		return fmt.Errorf("duplicate mismatch %x\n%s",
+			hash[:8], diffText)
+	}
+
+	return nil
+}
+
+// fetchDuplicateRecords reads duplicate payment records from the KV bucket.
+func fetchDuplicateRecords(paymentBucket kvdb.RBucket) ([]duplicateRecord,
+	error) {
+
+	dupBucket := paymentBucket.NestedReadBucket(duplicatePaymentsBucket)
+	if dupBucket == nil {
+		return nil, nil
+	}
+
+	var duplicates []duplicateRecord
+	err := dupBucket.ForEach(func(seqBytes, _ []byte) error {
+		if len(seqBytes) != 8 {
+			return nil
+		}
+
+		subBucket := dupBucket.NestedReadBucket(seqBytes)
+		if subBucket == nil {
+			return nil
+		}
+
+		creationData := subBucket.Get(duplicatePaymentCreationInfoKey)
+		if creationData == nil {
+			return fmt.Errorf("missing duplicate creation info")
+		}
+
+		creationInfo, err := deserializeDuplicatePaymentCreationInfo(
+			bytes.NewReader(creationData),
+		)
+		if err != nil {
+			return fmt.Errorf("deserialize duplicate creation "+
+				"info: %w", err)
+		}
+
+		settleData := subBucket.Get(duplicatePaymentSettleInfoKey)
+		failReasonData := subBucket.Get(duplicatePaymentFailInfoKey)
+
+		if settleData != nil && len(failReasonData) > 0 {
+			return fmt.Errorf("duplicate has both settle and " +
+				"fail info")
+		}
+
+		var (
+			failReason     sql.NullInt32
+			settlePreimage []byte
+			settleTime     sql.NullTime
+		)
+
+		switch {
+		case settleData != nil:
+			settlePreimage, settleTime, err =
+				parseDuplicateSettleData(settleData)
+			if err != nil {
+				return err
+			}
+		case len(failReasonData) > 0:
+			failReason = sql.NullInt32{
+				Int32: int32(failReasonData[0]),
+				Valid: true,
+			}
+		default:
+			// If the duplicate has no settle or fail info, it is
+			// considered failed. Every duplicate payment must have
+			// either a settle or fail info in the sql database. So
+			// we set the fail reason to error to mimic the behavior
+			// for the kv store.
+			failReason = sql.NullInt32{
+				Int32: int32(FailureReasonError),
+				Valid: true,
+			}
+		}
+
+		duplicates = append(duplicates, duplicateRecord{
+			AmountMsat: int64(creationInfo.Value),
+			CreatedAt: normalizeTimeForSQL(
+				creationInfo.CreationTime,
+			),
+			FailReason:     failReason,
+			SettlePreimage: settlePreimage,
+			SettleTime:     settleTime,
+		})
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return duplicates, nil
+}
+
+// dbDuplicatesToDuplicateRecords maps SQL duplicate rows into comparable
+// duplicate records.
+func dbDuplicatesToDuplicateRecords(
+	rows []sqlc.PaymentDuplicate) []duplicateRecord {
+
+	duplicates := make([]duplicateRecord, 0, len(rows))
+	for _, row := range rows {
+		duplicates = append(duplicates, duplicateRecord{
+			AmountMsat:     row.AmountMsat,
+			CreatedAt:      row.CreatedAt,
+			FailReason:     row.FailReason,
+			SettlePreimage: row.SettlePreimage,
+			SettleTime:     row.SettleTime,
+		})
+	}
+
+	return duplicates
+}
+
+// normalizeDuplicateRecords normalizes time precision and empty fields.
+func normalizeDuplicateRecords(records []duplicateRecord) []duplicateRecord {
+	if len(records) == 0 {
+		return []duplicateRecord{}
+	}
+
+	trunc := func(t time.Time) time.Time {
+		if t.IsZero() {
+			return t
+		}
+
+		return t.In(time.Local).Truncate(time.Microsecond)
+	}
+
+	for i := range records {
+		records[i].CreatedAt = trunc(records[i].CreatedAt)
+		if records[i].SettleTime.Valid {
+			records[i].SettleTime.Time = trunc(
+				records[i].SettleTime.Time,
+			)
+		}
+
+		if len(records[i].SettlePreimage) == 0 {
+			records[i].SettlePreimage = []byte{}
+		}
+	}
+
+	return records
+}
+
+// sortDuplicates orders records deterministically for deep comparison.
+func sortDuplicates(records []duplicateRecord) {
+	sort.SliceStable(records, func(i, j int) bool {
+		ai := records[i]
+		aj := records[j]
+
+		// Duplicates are "duplicates" because they share the same
+		// payment identifier. So ordering can be stable using
+		// timestamp + amount.
+		if !ai.CreatedAt.Equal(aj.CreatedAt) {
+			return ai.CreatedAt.Before(aj.CreatedAt)
+		}
+
+		return ai.AmountMsat < aj.AmountMsat
+	})
+}
+
+// validatePaymentCounts compares the number of migrated payments with the SQL
+// payment count to catch missing rows.
+func validatePaymentCounts(ctx context.Context, sqlDB SQLQueries,
+	expectedCount int64) error {
+
+	sqlCount, err := sqlDB.CountPayments(ctx)
+	if err != nil {
+		return fmt.Errorf("count SQL payments: %w", err)
+	}
+	if expectedCount != sqlCount {
+		return fmt.Errorf("payment count mismatch: kv=%d sql=%d",
+			expectedCount, sqlCount)
+	}
+
+	return nil
+}
diff --git a/payments/db/migration1/sql_migration.go b/payments/db/migration1/sql_migration.go
new file mode 100644
index 0000000..a7a02af
--- /dev/null
+++ b/payments/db/migration1/sql_migration.go
@@ -0,0 +1,817 @@
+package migration1
+
+import (
+	"bytes"
+	"context"
+	"database/sql"
+	"fmt"
+	"strconv"
+	"time"
+
+	"github.com/lightningnetwork/lnd/kvdb"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/payments/db/migration1/sqlc"
+	"golang.org/x/time/rate"
+)
+
+// MigrationStats tracks migration progress.
+type MigrationStats struct {
+	TotalPayments      int64
+	SuccessfulPayments int64
+	FailedPayments     int64
+	InFlightPayments   int64
+	InitiatedPayments  int64
+	TotalAttempts      int64
+	SettledAttempts    int64
+	FailedAttempts     int64
+	InFlightAttempts   int64
+	TotalHops          int64
+	DuplicatePayments  int64
+	DuplicateEntries   int64
+	SkippedPayments    int64
+	MigrationDuration  time.Duration
+}
+
+// MigratePaymentsKVToSQL migrates payments from KV to SQL and validates
+// migrated data in batches. Callers are responsible for executing this within
+// a single SQL transaction if atomicity is required.
+func MigratePaymentsKVToSQL(ctx context.Context, kvBackend kvdb.Backend,
+	sqlDB SQLQueries, cfg *SQLStoreConfig) error {
+
+	if cfg == nil {
+		return fmt.Errorf("missing SQL store config for migration")
+	}
+
+	if cfg.QueryCfg == nil {
+		return fmt.Errorf("missing SQL store config for " +
+			"validation")
+	}
+
+	if cfg.QueryCfg.MaxBatchSize == 0 {
+		return fmt.Errorf("invalid max batch size for " +
+			"validation")
+	}
+
+	stats := &MigrationStats{}
+	startTime := time.Now()
+
+	log.Infof("Starting payment migration from KV to SQL...")
+
+	var (
+		validationBatch   []migratedPaymentRef
+		validatedPayments int64
+
+		reportInterval     = rate.Sometimes{Interval: 5 * time.Second}
+		validationInterval = rate.Sometimes{Interval: 5 * time.Second}
+	)
+
+	// Open the KV backend in read-only mode.
+	err := kvBackend.View(func(kvTx kvdb.RTx) error {
+		// In case we start with an empty database, there are no
+		// payments to migrate.
+		paymentsBucket := kvTx.ReadBucket(paymentsRootBucket)
+		if paymentsBucket == nil {
+			log.Infof("No payments bucket found - database is " +
+				"empty")
+
+			return nil
+		}
+
+		// The index bucket maps sequence number -> payment hash.
+		indexes := kvTx.ReadBucket(paymentsIndexBucket)
+		if indexes == nil {
+			return fmt.Errorf("index bucket does not exist")
+		}
+
+		// We iterate over all sequence numbers in the index bucket to
+		// make sure we have the correct order of payments. Otherwise,
+		// if we just loop over the payments bucket, we might get the
+		// payments not in the chronological order but rather the
+		// lexicographical order of the payment hashes.
+		return indexes.ForEach(func(seqKey, indexVal []byte) error {
+			// Progress reporting based on time + actual work done.
+			reportProgress := func() {
+				elapsed := time.Since(startTime)
+				if elapsed <= 0 {
+					return
+				}
+
+				if stats.TotalPayments == 0 {
+					return
+				}
+
+				paymentRate := float64(stats.TotalPayments) /
+					elapsed.Seconds()
+				attemptRate := float64(stats.TotalAttempts) /
+					elapsed.Seconds()
+
+				log.Infof("Progress: %d payments, %d "+
+					"attempts, %d hops | Rate: %.1f "+
+					"pmt/s, %.1f att/s | Elapsed: %v",
+					stats.TotalPayments,
+					stats.TotalAttempts, stats.TotalHops,
+					paymentRate, attemptRate,
+					elapsed.Round(time.Second),
+				)
+			}
+
+			reportInterval.Do(reportProgress)
+
+			r := bytes.NewReader(indexVal)
+			paymentHash, err := deserializePaymentIndex(r)
+			if err != nil {
+				return err
+			}
+
+			paymentBucket := paymentsBucket.NestedReadBucket(
+				paymentHash[:],
+			)
+			if paymentBucket == nil {
+				// We skip the entry in case this sequence
+				// number does not have a corresponding
+				// payment bucket. But aborting would not help
+				// either because it is just a db inconsistency.
+				log.Warnf("Missing bucket for payment %x",
+					paymentHash[:8])
+
+				stats.SkippedPayments++
+
+				return nil
+			}
+
+			// Every payment bucket should have a sequence number
+			// which is also important to check for duplicates.
+			seqBytes := paymentBucket.Get(paymentSequenceKey)
+			if seqBytes == nil {
+				return ErrNoSequenceNumber
+			}
+
+			// Skip duplicates. They are migrated into the
+			// payment_duplicates table when the primary payment is
+			// processed.
+			if !bytes.Equal(seqBytes, seqKey) {
+				return nil
+			}
+
+			// Fetch the payment from the kv store.
+			payment, err := fetchPayment(paymentBucket)
+			if err != nil {
+				return fmt.Errorf("fetch payment %x: %w",
+					paymentHash[:8], err)
+			}
+
+			// Migrate the payment to the SQL database.
+			paymentID, err := migratePayment(
+				ctx, payment, paymentHash, sqlDB, stats,
+			)
+			if err != nil {
+				return fmt.Errorf("migrate payment %x: %w",
+					paymentHash[:8], err)
+			}
+
+			// Check for duplicates.
+			dupBucket := paymentBucket.NestedReadBucket(
+				duplicatePaymentsBucket,
+			)
+			if dupBucket != nil {
+				err = migrateDuplicatePayments(
+					ctx, dupBucket, paymentHash,
+					paymentID, sqlDB, stats,
+				)
+				if err != nil {
+					return fmt.Errorf("migrate duplicates "+
+						"%x: %w", paymentHash[:8],
+						err)
+				}
+			}
+
+			// Add the payment to the validation batch.
+			validationBatch = append(
+				validationBatch, migratedPaymentRef{
+					Hash:      paymentHash,
+					PaymentID: paymentID,
+				},
+			)
+			if uint32(len(validationBatch)) >=
+				cfg.QueryCfg.MaxBatchSize {
+
+				err := validateMigratedPaymentBatch(
+					ctx, kvBackend, sqlDB,
+					cfg,
+					validationBatch,
+				)
+				if err != nil {
+					return err
+				}
+
+				validatedPayments += int64(
+					len(validationBatch),
+				)
+
+				// Log validation progress periodically.
+				validationInterval.Do(func() {
+					log.Infof("Validated %d/%d "+
+						"payments",
+						validatedPayments,
+						stats.TotalPayments,
+					)
+				})
+
+				validationBatch = validationBatch[:0]
+			}
+
+			return nil
+		})
+	}, func() {})
+
+	if err != nil {
+		return fmt.Errorf("migrate payments: %w", err)
+	}
+
+	// Validate any remaining payments in the batch.
+	if len(validationBatch) > 0 {
+		if err := validateMigratedPaymentBatch(
+			ctx, kvBackend, sqlDB, cfg, validationBatch,
+		); err != nil {
+			return err
+		}
+
+		validatedPayments += int64(len(validationBatch))
+		log.Infof("Validated %d/%d payments", validatedPayments,
+			stats.TotalPayments)
+	}
+
+	// Validate the total number of payments as an additional sanity check.
+	if err := validatePaymentCounts(
+		ctx, sqlDB, stats.TotalPayments,
+	); err != nil {
+		return err
+	}
+
+	stats.MigrationDuration = time.Since(startTime)
+
+	printMigrationSummary(stats)
+
+	return nil
+}
+
+// normalizeTimeForSQL converts a timestamp into the representation we persist
+// and compare against in SQL:
+// - drops any monotonic clock reading (SQL can't store it),
+// - forces UTC for deterministic comparisons across environments.
+//
+// A zero time is returned unchanged.
+func normalizeTimeForSQL(t time.Time) time.Time {
+	if t.IsZero() {
+		return t
+	}
+
+	return time.Unix(0, t.UnixNano()).UTC()
+}
+
+// migratePayment migrates a single payment from KV to SQL.
+func migratePayment(ctx context.Context, payment *MPPayment, hash lntypes.Hash,
+	sqlDB SQLQueries, stats *MigrationStats) (int64, error) {
+
+	// Update migration stats based on payment status.
+	switch payment.Status {
+	case StatusSucceeded:
+		stats.SuccessfulPayments++
+
+	case StatusFailed:
+		stats.FailedPayments++
+
+	case StatusInFlight:
+		stats.InFlightPayments++
+
+	case StatusInitiated:
+		stats.InitiatedPayments++
+	}
+
+	// Prepare fail reason for SQL insert.
+	var failReason sql.NullInt32
+	if payment.FailureReason != nil {
+		failReason = sql.NullInt32{
+			Int32: int32(*payment.FailureReason),
+			Valid: true,
+		}
+	}
+
+	// Insert payment using migration query.
+	paymentID, err := sqlDB.InsertPaymentMig(
+		ctx, sqlc.InsertPaymentMigParams{
+			AmountMsat: int64(payment.Info.Value),
+			CreatedAt: normalizeTimeForSQL(
+				payment.Info.CreationTime,
+			),
+			PaymentIdentifier: hash[:],
+			FailReason:        failReason,
+		})
+	if err != nil {
+		return 0, fmt.Errorf("insert payment: %w", err)
+	}
+
+	// Insert payment intent.
+	//
+	// Only insert a row if we have an actual intent payload. For legacy
+	// hash-only/keysend-style payments, the intent may be absent.
+	if len(payment.Info.PaymentRequest) > 0 {
+		_, err = sqlDB.InsertPaymentIntent(
+			ctx, sqlc.InsertPaymentIntentParams{
+				PaymentID:     paymentID,
+				IntentType:    int16(PaymentIntentTypeBolt11),
+				IntentPayload: payment.Info.PaymentRequest,
+			},
+		)
+		if err != nil {
+			return 0, fmt.Errorf("insert intent: %w", err)
+		}
+	}
+
+	// Insert first hop custom records (payment level).
+	for key, value := range payment.Info.FirstHopCustomRecords {
+		err = sqlDB.InsertPaymentFirstHopCustomRecord(ctx,
+			sqlc.InsertPaymentFirstHopCustomRecordParams{
+				PaymentID: paymentID,
+				Key:       int64(key),
+				Value:     value,
+			},
+		)
+		if err != nil {
+			return 0, fmt.Errorf("insert custom record: %w", err)
+		}
+	}
+
+	// Migrate HTLC attempts.
+	for _, htlc := range payment.HTLCs {
+		err = migrateHTLCAttempt(
+			ctx, paymentID, hash, &htlc, sqlDB, stats,
+		)
+		if err != nil {
+			return 0, fmt.Errorf("migrate attempt %d: %w",
+				htlc.AttemptID, err)
+		}
+	}
+
+	stats.TotalPayments++
+
+	return paymentID, nil
+}
+
+// migrateHTLCAttempt migrates a single HTLC attempt.
+func migrateHTLCAttempt(ctx context.Context, paymentID int64,
+	parentPaymentHash lntypes.Hash, htlc *HTLCAttempt, sqlDB SQLQueries,
+	stats *MigrationStats) error {
+
+	// Validate that we have a payment hash for the attempt.
+	//
+	// NOTE: We always require an attempt payment hash. A missing hash is an
+	// unrecoverable inconsistency. All payments should have a payment hash
+	// (AMP,MPP,Legacy)
+	var paymentHash []byte
+	switch {
+	case htlc.Hash != nil:
+		paymentHash = (*htlc.Hash)[:]
+
+	default:
+		return fmt.Errorf("HTLC attempt %d missing payment hash "+
+			"(parent payment hash=%x)", htlc.AttemptID,
+			parentPaymentHash[:])
+	}
+
+	firstHopAmountMsat := int64(htlc.Route.FirstHopAmount.Val.Int())
+
+	// Get the session key bytes.
+	sessionKeyBytes := htlc.SessionKey().Serialize()
+
+	// Insert HTLC attempt.
+	_, err := sqlDB.InsertHtlcAttempt(ctx, sqlc.InsertHtlcAttemptParams{
+		PaymentID:          paymentID,
+		AttemptIndex:       int64(htlc.AttemptID),
+		SessionKey:         sessionKeyBytes,
+		AttemptTime:        normalizeTimeForSQL(htlc.AttemptTime),
+		PaymentHash:        paymentHash,
+		FirstHopAmountMsat: firstHopAmountMsat,
+		RouteTotalTimeLock: int32(htlc.Route.TotalTimeLock),
+		RouteTotalAmount:   int64(htlc.Route.TotalAmount),
+		RouteSourceKey:     htlc.Route.SourcePubKey[:],
+	})
+	if err != nil {
+		return fmt.Errorf("insert HTLC attempt: %w", err)
+	}
+
+	// Insert the route-level first hop custom records.
+	for key, value := range htlc.Route.FirstHopWireCustomRecords {
+		err = sqlDB.InsertPaymentAttemptFirstHopCustomRecord(
+			ctx,
+			sqlc.InsertPaymentAttemptFirstHopCustomRecordParams{
+				HtlcAttemptIndex: int64(htlc.AttemptID),
+				Key:              int64(key),
+				Value:            value,
+			},
+		)
+		if err != nil {
+			return fmt.Errorf("insert attempt first hop custom "+
+				"record: %w", err)
+		}
+	}
+
+	// Insert route hops.
+	for hopIndex := range htlc.Route.Hops {
+		hop := htlc.Route.Hops[hopIndex]
+		err = migrateRouteHop(
+			ctx, int64(htlc.AttemptID), hopIndex, hop,
+			sqlDB, stats,
+		)
+		if err != nil {
+			return fmt.Errorf("migrate hop %d: %w", hopIndex, err)
+		}
+	}
+
+	// Handle attempt resolution (settle or fail).
+	switch {
+	case htlc.Settle != nil:
+		// Settled
+		err = sqlDB.SettleAttempt(ctx, sqlc.SettleAttemptParams{
+			AttemptIndex: int64(htlc.AttemptID),
+			ResolutionTime: normalizeTimeForSQL(
+				htlc.Settle.SettleTime,
+			),
+			ResolutionType: int32(HTLCAttemptResolutionSettled),
+			SettlePreimage: htlc.Settle.Preimage[:],
+		})
+		if err != nil {
+			return fmt.Errorf("settle attempt: %w", err)
+		}
+
+		stats.SettledAttempts++
+
+	case htlc.Failure != nil:
+		var failureMsg bytes.Buffer
+		if htlc.Failure.Message != nil {
+			err := lnwire.EncodeFailureMessage(
+				&failureMsg, htlc.Failure.Message, 0,
+			)
+			if err != nil {
+				return fmt.Errorf("failed to encode "+
+					"failure message: %w", err)
+			}
+		}
+
+		err = sqlDB.FailAttempt(ctx, sqlc.FailAttemptParams{
+			AttemptIndex: int64(htlc.AttemptID),
+			ResolutionTime: normalizeTimeForSQL(
+				htlc.Failure.FailTime,
+			),
+			ResolutionType: int32(HTLCAttemptResolutionFailed),
+			FailureSourceIndex: sql.NullInt32{
+				Int32: int32(htlc.Failure.FailureSourceIndex),
+				Valid: true,
+			},
+			HtlcFailReason: sql.NullInt32{
+				Int32: int32(htlc.Failure.Reason),
+				Valid: true,
+			},
+			FailureMsg: failureMsg.Bytes(),
+		})
+		if err != nil {
+			return fmt.Errorf("fail attempt: %w", err)
+		}
+
+		stats.FailedAttempts++
+
+	default:
+		// If the attempt is not settled or failed, it is in flight.
+		stats.InFlightAttempts++
+	}
+
+	stats.TotalAttempts++
+
+	return nil
+}
+
+// migrateRouteHop migrates a single route hop.
+func migrateRouteHop(ctx context.Context,
+	attemptID int64, hopIndex int, hop *Hop, sqlDB SQLQueries,
+	stats *MigrationStats) error {
+
+	// Convert channel ID to string representation of uint64.
+	// The SCID is stored as a decimal string to match the converter
+	// expectations (sql_converters.go:173).
+	scidStr := strconv.FormatUint(hop.ChannelID, 10)
+
+	// Insert route hop.
+	hopID, err := sqlDB.InsertRouteHop(ctx, sqlc.InsertRouteHopParams{
+		HtlcAttemptIndex: attemptID,
+		HopIndex:         int32(hopIndex),
+		PubKey:           hop.PubKeyBytes[:],
+		Scid:             scidStr,
+		OutgoingTimeLock: int32(hop.OutgoingTimeLock),
+		AmtToForward:     int64(hop.AmtToForward),
+		MetaData:         hop.Metadata,
+	})
+	if err != nil {
+		return fmt.Errorf("insert hop: %w", err)
+	}
+
+	// Check for blinded route data (route blinding).
+	if len(hop.EncryptedData) > 0 || hop.BlindingPoint != nil ||
+		hop.TotalAmtMsat != 0 {
+
+		var blindingPoint []byte
+		if hop.BlindingPoint != nil {
+			blindingPoint = hop.BlindingPoint.SerializeCompressed()
+		}
+
+		var totalAmt sql.NullInt64
+		if hop.TotalAmtMsat != 0 {
+			totalAmt = sql.NullInt64{
+				Int64: int64(hop.TotalAmtMsat),
+				Valid: true,
+			}
+		}
+
+		err := sqlDB.InsertRouteHopBlinded(
+			ctx, sqlc.InsertRouteHopBlindedParams{
+				HopID:               hopID,
+				EncryptedData:       hop.EncryptedData,
+				BlindingPoint:       blindingPoint,
+				BlindedPathTotalAmt: totalAmt,
+			},
+		)
+		if err != nil {
+			return fmt.Errorf("insert blinded hop: %w", err)
+		}
+	}
+
+	// Check for MPP record.
+	if hop.MPP != nil {
+		paymentAddr := hop.MPP.PaymentAddr()
+		err = sqlDB.InsertRouteHopMpp(ctx, sqlc.InsertRouteHopMppParams{
+			HopID:       hopID,
+			PaymentAddr: paymentAddr[:],
+			TotalMsat:   int64(hop.MPP.TotalMsat()),
+		})
+		if err != nil {
+			return fmt.Errorf("insert MPP: %w", err)
+		}
+	}
+
+	// Check for AMP record.
+	if hop.AMP != nil {
+		rootShare := hop.AMP.RootShare()
+		setID := hop.AMP.SetID()
+		err = sqlDB.InsertRouteHopAmp(ctx, sqlc.InsertRouteHopAmpParams{
+			HopID:      hopID,
+			RootShare:  rootShare[:],
+			SetID:      setID[:],
+			ChildIndex: int32(hop.AMP.ChildIndex()),
+		})
+		if err != nil {
+			return fmt.Errorf("insert AMP: %w", err)
+		}
+	}
+
+	// Check for custom records.
+	if hop.CustomRecords != nil {
+		for tlvType, value := range hop.CustomRecords {
+			err = sqlDB.InsertPaymentHopCustomRecord(
+				ctx,
+				sqlc.InsertPaymentHopCustomRecordParams{
+					HopID: hopID,
+					Key:   int64(tlvType),
+					Value: value,
+				},
+			)
+			if err != nil {
+				return fmt.Errorf("insert hop custom "+
+					"record: %w", err)
+			}
+		}
+	}
+
+	stats.TotalHops++
+
+	return nil
+}
+
+// migrateDuplicatePayments migrates duplicate payments into the dedicated
+// payment_duplicates table.
+func migrateDuplicatePayments(ctx context.Context, dupBucket kvdb.RBucket,
+	hash [32]byte, primaryPaymentID int64, sqlDB SQLQueries,
+	stats *MigrationStats) error {
+
+	duplicateCount := 0
+
+	err := dupBucket.ForEach(func(seqBytes, _ []byte) error {
+		// The duplicates bucket should only contain nested buckets
+		// keyed by 8-byte sequence numbers. Skip any unexpected keys
+		// (defensive check for corrupted or malformed data).
+		if len(seqBytes) != 8 {
+			log.Warnf("Skipping unexpected key in duplicates "+
+				"bucket for payment %x: key length %d, "+
+				"expected 8",
+				hash[:8], len(seqBytes),
+			)
+
+			return nil
+		}
+
+		seqNum := byteOrder.Uint64(seqBytes)
+		subBucket := dupBucket.NestedReadBucket(seqBytes)
+		if subBucket == nil {
+			return nil
+		}
+
+		duplicateCount++
+		log.Infof("Migrating duplicate payment seq=%d for "+
+			"payment %x", seqNum, hash[:8])
+
+		err := migrateSingleDuplicatePayment(
+			ctx, subBucket, hash, primaryPaymentID, seqNum,
+			sqlDB,
+		)
+		if err != nil {
+			return fmt.Errorf(
+				"migrate duplicate payment seq=%d: %w",
+				seqNum, err,
+			)
+		}
+
+		return nil
+	})
+
+	if duplicateCount > 0 {
+		stats.DuplicatePayments++
+		stats.DuplicateEntries += int64(duplicateCount)
+
+		log.Infof("Payment %x had %d duplicate(s) migrated", hash[:8],
+			duplicateCount)
+	}
+
+	return err
+}
+
+// migrateSingleDuplicatePayment inserts a duplicate payment record for the
+// given payment hash into payment_duplicates.
+func migrateSingleDuplicatePayment(ctx context.Context, dupBucket kvdb.RBucket,
+	hash [32]byte, primaryPaymentID int64, duplicateSeq uint64,
+	sqlDB SQLQueries) error {
+
+	creationData := dupBucket.Get(duplicatePaymentCreationInfoKey)
+	if creationData == nil {
+		return fmt.Errorf("duplicate payment seq=%d missing "+
+			"creation info (payment=%x)", duplicateSeq, hash[:8])
+	}
+
+	creationInfo, err := deserializeDuplicatePaymentCreationInfo(
+		bytes.NewReader(creationData),
+	)
+	if err != nil {
+		return fmt.Errorf("deserialize duplicate creation "+
+			"info: %w", err)
+	}
+
+	settleData := dupBucket.Get(duplicatePaymentSettleInfoKey)
+	failReasonData := dupBucket.Get(duplicatePaymentFailInfoKey)
+	attemptData := dupBucket.Get(duplicatePaymentAttemptInfoKey)
+
+	if settleData != nil && len(failReasonData) > 0 {
+		return fmt.Errorf("duplicate payment seq=%d has both "+
+			"settle and fail info (payment=%x)", duplicateSeq,
+			hash[:8])
+	}
+
+	var (
+		failReason     sql.NullInt32
+		settlePreimage []byte
+		settleTime     sql.NullTime
+	)
+
+	switch {
+	case settleData != nil:
+		settlePreimage, settleTime, err = parseDuplicateSettleData(
+			settleData,
+		)
+		if err != nil {
+			return err
+		}
+
+	case len(failReasonData) > 0:
+		failReason = sql.NullInt32{
+			Int32: int32(failReasonData[0]),
+			Valid: true,
+		}
+
+	default:
+		// If the duplicate payment has no settle or fail info,
+		// we mark it as failed during the migration. Duplicate
+		// payments were a bug in older versions of LND, so we can be
+		// sure if a duplicate payment has no failure reason or
+		// settlement data, the corresponding HTLC for this payment
+		// has been failed (resolved).
+		if attemptData == nil {
+			log.Warnf("Duplicate payment seq=%d has no "+
+				"attempt info and no resolution (payment=%x); "+
+				"marking failed", duplicateSeq, hash[:8])
+		} else {
+			log.Warnf("Duplicate payment seq=%d has attempt "+
+				"info but no resolution (payment=%x); "+
+				"marking failed", duplicateSeq, hash[:8])
+		}
+
+		failReason = sql.NullInt32{
+			Int32: int32(FailureReasonError),
+			Valid: true,
+		}
+	}
+
+	_, err = sqlDB.InsertPaymentDuplicateMig(
+		ctx, sqlc.InsertPaymentDuplicateMigParams{
+			PaymentID:  primaryPaymentID,
+			AmountMsat: int64(creationInfo.Value),
+			CreatedAt: normalizeTimeForSQL(
+				creationInfo.CreationTime,
+			),
+			FailReason:     failReason,
+			SettlePreimage: settlePreimage,
+			SettleTime:     settleTime,
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("insert duplicate payment: %w", err)
+	}
+
+	return nil
+}
+
+// parseDuplicateSettleData extracts settle data from either legacy or modern
+// duplicate formats.
+func parseDuplicateSettleData(settleData []byte) ([]byte, sql.NullTime, error) {
+	if len(settleData) == lntypes.PreimageSize {
+		return append([]byte(nil), settleData...), sql.NullTime{}, nil
+	}
+
+	settleInfo, err := deserializeHTLCSettleInfo(
+		bytes.NewReader(settleData),
+	)
+	if err != nil {
+		return nil, sql.NullTime{},
+			fmt.Errorf("deserialize duplicate settle: %w", err)
+	}
+
+	settleTime := normalizeTimeForSQL(settleInfo.SettleTime)
+
+	return settleInfo.Preimage[:], sql.NullTime{
+		Time:  settleTime,
+		Valid: !settleTime.IsZero(),
+	}, nil
+}
+
+// printMigrationSummary prints a summary of the migration.
+func printMigrationSummary(stats *MigrationStats) {
+	if stats.TotalPayments == 0 {
+		log.Infof("No payments migrated - database is empty")
+
+		return
+	}
+
+	log.Infof("========================================")
+	log.Infof("   Payment Migration Summary")
+	log.Infof("========================================")
+	log.Infof("Total Payments:        %d", stats.TotalPayments)
+	log.Infof("  Successful:       %d", stats.SuccessfulPayments)
+	log.Infof("  Failed:           %d", stats.FailedPayments)
+	log.Infof("  In-Flight:        %d", stats.InFlightPayments)
+	log.Infof("  Initiated:        %d", stats.InitiatedPayments)
+	log.Infof("")
+	log.Infof("Total HTLC Attempts:   %d", stats.TotalAttempts)
+	log.Infof("  Settled:          %d", stats.SettledAttempts)
+	log.Infof("  Failed:           %d", stats.FailedAttempts)
+	log.Infof("  In-Flight:        %d", stats.InFlightAttempts)
+	log.Infof("")
+	log.Infof("Total Route Hops:      %d", stats.TotalHops)
+
+	if stats.SkippedPayments > 0 {
+		log.Infof("")
+		log.Warnf("SKIPPED PAYMENTS:")
+		log.Warnf("  Indexed payments with missing buckets: %d",
+			stats.SkippedPayments)
+		log.Warnf("  These indicate minor DB inconsistencies.")
+	}
+
+	if stats.DuplicatePayments > 0 {
+		log.Infof("")
+		log.Warnf("DUPLICATE PAYMENTS DETECTED:")
+		log.Warnf("  Unique payment hashes with duplicates: %d",
+			stats.DuplicatePayments)
+		log.Warnf("  Total duplicate entries migrated:      %d",
+			stats.DuplicateEntries)
+		log.Warnf("  These were caused by an old LND bug.")
+	}
+
+	log.Infof("")
+	log.Infof("Migration Duration:    %v", stats.MigrationDuration)
+	log.Infof("========================================")
+}