YarnAssetPostProcessor.cs

using UnityEngine;
using UnityEditor;
using Yarn.Unity;
using System.Collections.Generic;
using System.IO;

class YarnAssetPostProcessor : AssetPostprocessor
{
    private const string ScriptFolder = "Assets/Yarn/";
    private static readonly string _filePath = ScriptFolder + "YarnNodesRef.cs";
    
    static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths, bool didDomainReload)
    {
        foreach (string str in importedAssets)
        {
            if (str.ToLowerInvariant().EndsWith(".yarnproject"))
            {
                OnYarnProjectChanged();
            }
        }
    }

    private static YarnProject GetYarnProject()
    {
        var assetGUIDs = AssetDatabase.FindAssets("t: YarnProject");
        if (assetGUIDs.Length <= 0)
        {
            Debug.LogError("Yarn Project not found");
            return null;
        }
        var assetPath = AssetDatabase.GUIDToAssetPath(assetGUIDs[0]);
        return AssetDatabase.LoadAssetAtPath<YarnProject>(assetPath);
    }

    private static void OnYarnProjectChanged()
    {
        var project = GetYarnProject();
        if( NodesChanged( project.NodeNames ) )
        {
            GenerateNodeReferenceClass();   
        }
    }

    private static bool NodesChanged(string[] projectNodeNames)
    {
        var infile = YarnNodesRef.All;
        if (infile.Length != projectNodeNames.Length) return true;
        foreach (var projectNodeName in projectNodeNames)
        {
            var nodeFound = false;
            foreach (var classNodeName in infile)
            {
                if (classNodeName == projectNodeName)
                {
                    nodeFound = true;
                    break;
                }
            }
            if (!nodeFound) return true;
        }
        return false;
    }
    
    public static void GenerateNodeReferenceClass()
    {
        var nodeNames = GetYarnProject().NodeNames;
        var sceneList = new List<string>();
        var nodesMap = new Dictionary<string, List<string>>();
        foreach (var nodeName in nodeNames)
        {
            var underscoreIndex = nodeName.IndexOf('_');
            if (underscoreIndex == -1)
            {
                Debug.LogWarning("node name has no prefix! "+nodeName);
                continue;
            }
            var prefix = nodeName[..underscoreIndex];
            if (prefix.Length > 4)
            {
                Debug.LogWarning("node name prefix too long! "+nodeName);
            }
            if (!sceneList.Contains(prefix))
            {
                sceneList.Add(prefix);
                nodesMap.Add(prefix, new List<string>());
            }
            nodesMap[prefix].Add(nodeName);
        }
        
        using StreamWriter outfile = new StreamWriter(_filePath, false);
        var listofall = new List<string>(); //keep track of all added constants
        // Class contents generation
        outfile.WriteLine("/// <summary>");
        outfile.WriteLine("/// Auto-generated class");
        outfile.WriteLine("/// </summary>");
        outfile.WriteLine("");
        outfile.WriteLine("public static class YarnNodesRef");
        outfile.WriteLine("{");
        foreach (var prefix in sceneList)
        {
            var nodes = nodesMap[prefix];
            outfile.WriteLine("public static class "+prefix); //nested class for each prefix
            outfile.WriteLine("{");
            if (nodes != null)
            {
                for (var i = 0; i < nodes.Count; i++)
                {
                    var node = nodes[i];
                    if (node == null)
                    {
                        Debug.LogWarning("node name is NULL");
                        continue;
                    }
                    var nameWithoutPrefix = node.Replace(prefix+"_", "");
                    outfile.WriteLine("\tpublic static string " + nameWithoutPrefix + " = \"" + node + "\";");
                    listofall.Add(prefix+"."+nameWithoutPrefix);
                }
            }
            outfile.WriteLine("}");
        }
        outfile.WriteLine("public static string[] All = {");
        foreach (var item in listofall)
        {
            outfile.WriteLine(item+",");
        }
        outfile.WriteLine("};");
        outfile.WriteLine("}");
    }
}

YarnNodesRef.cs

/// <summary>
/// Auto-generated class
/// </summary>

public static class YarnNodesRef
{
    public static string[] All = {
};
}

This utility for YarnSpinner in Unity generates a static class for easy references to nodes. You can start dialogs by writing stuff like StartDialog(YarnNodesRef.Scene1.Introduction). It assumes you use prefixes with your node names like node name is Scene1_Introduction.