payments/migration1: wire KV→SQL migration in the main pkg

diff --git a/config_builder.go b/config_builder.go
index 74f8b3a..729cb60 100644
--- a/config_builder.go
+++ b/config_builder.go
@@ -51,6 +51,8 @@ import (
 	"github.com/lightningnetwork/lnd/macaroons"
 	"github.com/lightningnetwork/lnd/msgmux"
 	paymentsdb "github.com/lightningnetwork/lnd/payments/db"
+	paymentsmig1 "github.com/lightningnetwork/lnd/payments/db/migration1"
+	paymentsmig1sqlc "github.com/lightningnetwork/lnd/payments/db/migration1/sqlc"
 	"github.com/lightningnetwork/lnd/rpcperms"
 	"github.com/lightningnetwork/lnd/signal"
 	"github.com/lightningnetwork/lnd/sqldb"
@@ -76,6 +78,10 @@ const (
 	// graphMigration is the version number for the graph migration
 	// that migrates the KV graph to the native SQL schema.
 	graphMigration = 10
+
+	// paymentMigration is the version number for the payments migration
+	// that migrates KV payments to the native SQL schema.
+	paymentMigration = 14
 )
 
 // GrpcRegistrar is an interface that must be satisfied by an external subserver
@@ -1153,6 +1159,31 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 				return nil
 			}
 
+			paymentMig := func(tx *sqlc.Queries) error {
+				err := paymentsmig1.MigratePaymentsKVToSQL(
+					ctx,
+					dbs.ChanStateDB.Backend,
+					paymentsmig1sqlc.New(tx.GetTx()),
+					&paymentsmig1.SQLStoreConfig{
+						QueryCfg: queryCfg,
+					},
+				)
+				if err != nil {
+					return fmt.Errorf("failed to migrate "+
+						"payments to SQL: %w", err)
+				}
+
+				// Set the payments bucket tombstone to
+				// indicate that the migration has been
+				// completed.
+				d.logger.Debugf("Setting payments bucket " +
+					"tombstone")
+
+				return paymentsdb.SetPaymentsBucketTombstone(
+					dbs.ChanStateDB.Backend,
+				)
+			}
+
 			// Make sure we attach the custom migration function to
 			// the correct migration version.
 			for i := 0; i < len(migrations); i++ {
@@ -1162,11 +1193,17 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 					migrations[i].MigrationFn = invoiceMig
 
 					continue
+
 				case graphMigration:
 					migrations[i].MigrationFn = graphMig
 
 					continue
 
+				case paymentMigration:
+					migrations[i].MigrationFn = paymentMig
+
+					continue
+
 				default:
 				}
 
@@ -1265,6 +1302,27 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 			return nil, nil, err
 		}
 
+		// Check if the payments bucket tombstone is set. If it is, we
+		// need to return and ask the user switch back to using the
+		// native SQL store.
+		ripPayments, err := paymentsdb.GetPaymentsBucketTombstone(
+			dbs.ChanStateDB.Backend,
+		)
+		if err != nil {
+			err = fmt.Errorf("unable to check payments bucket "+
+				"tombstone: %w", err)
+			d.logger.Error(err)
+
+			return nil, nil, err
+		}
+		if ripPayments {
+			err = fmt.Errorf("payments bucket tombstoned, please " +
+				"switch back to native SQL")
+			d.logger.Error(err)
+
+			return nil, nil, err
+		}
+
 		dbs.InvoiceDB = dbs.ChanStateDB
 
 		graphStore, err = graphdb.NewKVStore(
diff --git a/payments/db/kv_tombstone.go b/payments/db/kv_tombstone.go
new file mode 100644
index 0000000..7dc13b9
--- /dev/null
+++ b/payments/db/kv_tombstone.go
@@ -0,0 +1,71 @@
+package paymentsdb
+
+import (
+	"fmt"
+
+	"github.com/lightningnetwork/lnd/kvdb"
+)
+
+var (
+	// paymentsBucketTombstone is the key used to mark the payments bucket
+	// as permanently closed after a successful migration.
+	paymentsBucketTombstone = []byte("payments-tombstone")
+)
+
+// SetPaymentsBucketTombstone sets the tombstone key in the payments bucket to
+// mark the bucket as permanently closed. This prevents it from being reopened
+// in the future.
+func SetPaymentsBucketTombstone(db kvdb.Backend) error {
+	return kvdb.Update(db, func(tx kvdb.RwTx) error {
+		// Access the top-level payments bucket.
+		payments := tx.ReadWriteBucket(paymentsRootBucket)
+
+		// In case the bucket doesn't exist, because we start
+		// immediately with the native SQL schema, we create it as well
+		// to make sure the user cannot switch back to the KV store.
+		if payments == nil {
+			var err error
+			payments, err = tx.CreateTopLevelBucket(
+				paymentsRootBucket,
+			)
+			if err != nil {
+				return fmt.Errorf("failed to create payments "+
+					"bucket: %w", err)
+			}
+		}
+
+		// Add the tombstone key to the payments bucket.
+		err := payments.Put(paymentsBucketTombstone, []byte("1"))
+		if err != nil {
+			return fmt.Errorf("failed to set tombstone: %w", err)
+		}
+
+		return nil
+	}, func() {})
+}
+
+// GetPaymentsBucketTombstone checks if the tombstone key exists in the payments
+// bucket. It returns true if the tombstone is present and false otherwise.
+func GetPaymentsBucketTombstone(db kvdb.Backend) (bool, error) {
+	var tombstoneExists bool
+
+	err := kvdb.View(db, func(tx kvdb.RTx) error {
+		// Access the top-level payments bucket.
+		payments := tx.ReadBucket(paymentsRootBucket)
+		if payments == nil {
+			tombstoneExists = false
+			return nil
+		}
+
+		// Check if the tombstone key exists.
+		tombstone := payments.Get(paymentsBucketTombstone)
+		tombstoneExists = tombstone != nil
+
+		return nil
+	}, func() {})
+	if err != nil {
+		return false, err
+	}
+
+	return tombstoneExists, nil
+}
diff --git a/payments/db/log.go b/payments/db/log.go
index 8a77dbc..c889234 100644
--- a/payments/db/log.go
+++ b/payments/db/log.go
@@ -3,6 +3,7 @@ package paymentsdb
 import (
 	"github.com/btcsuite/btclog/v2"
 	"github.com/lightningnetwork/lnd/build"
+	paymentsmig1 "github.com/lightningnetwork/lnd/payments/db/migration1"
 )
 
 // log is a logger that is initialized with no output filters.  This
@@ -29,4 +30,5 @@ func DisableLog() {
 // using btclog.
 func UseLogger(logger btclog.Logger) {
 	log = logger
+	paymentsmig1.UseLogger(logger)
 }
diff --git a/sqldb/migrations_dev.go b/sqldb/migrations_dev.go
index ca57cf0..7b02b15 100644
--- a/sqldb/migrations_dev.go
+++ b/sqldb/migrations_dev.go
@@ -8,4 +8,18 @@ var migrationAdditions = []MigrationConfig{
 		Version:       12,
 		SchemaVersion: 10,
 	},
+	{
+		Name:          "000011_payment_duplicates",
+		Version:       13,
+		SchemaVersion: 11,
+	},
+	{
+		Name:          "kv_payments_migration",
+		Version:       14,
+		SchemaVersion: 11,
+		// A migration function may be attached to this
+		// migration to migrate KV payments to the native SQL
+		// schema. This is optional and can be disabled by the
+		// user if necessary.
+	},
 }