lnd: add clarifiying comment when introducing a new db

config_prod.go

@@ -9,6 +9,16 @@ import (
 	"github.com/lightningnetwork/lnd/sqldb/sqlc"
 )
 
+// NOTE: This file (together with config_test_native_sql.go) contains
+// build-tag-specific overrides that control which backend is used for certain
+// stores. If any function in either file switches a store between KV and native
+// SQL depending on the build tag, and the corresponding migration is later
+// promoted from sqldb/migrations_dev.go into the mainline sqldb/migrations.go,
+// you must also update the UseNativeSQL branch in BuildDatabase
+// (config_builder.go) to use the native SQL backend for that store. Promoting
+// the migration without updating the store means the production build will
+// continue writing to the KV backend instead of SQL.
+
 // RunTestSQLMigration is a build tag that indicates whether the test_native_sql
 // build tag is set.
 var RunTestSQLMigration = false