add scene toolbar tool

My project/Assets/Prefabs/Managers.meta

+fileFormatVersion: 2
+guid: aa7b3186c161cb146a4d7e1ef3adf89c
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

My project/Assets/Prefabs/TF/Phone Art/Envrionment(Clone).prefab.meta

-fileFormatVersion: 2
-guid: e7ce1812f530d4b4ebb33e3f2bc608b4
-PrefabImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

My project/Assets/Resources/Scene Collections.meta

+fileFormatVersion: 2
+guid: f221bf2bdc917c146a8049f4dbdfc2ba
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

My project/Assets/Resources/Scene Collections/NewSceneCollection.asset

+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!114 &11400000
+MonoBehaviour:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 0}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: 9d12c215cf29fa446abc76913d213425, type: 3}
+  m_Name: NewSceneCollection
+  m_EditorClassIdentifier: Assembly-CSharp::EditorSceneCollection
+  collectionName: MainScenes
+  description: 
+  showInMainMenu: 1
+  sceneAssets:
+  - {fileID: 102900000, guid: 70e093a0ef85a3e418cc77c732bc9e48, type: 3}
+  - {fileID: 102900000, guid: c2f60049cef0f6b44b9445afcf550aff, type: 3}
+  - {fileID: 102900000, guid: 89a5ca01ddc649a498cda8dc02cf28e3, type: 3}

My project/Assets/Resources/Scene Collections/NewSceneCollection.asset.meta

+fileFormatVersion: 2
+guid: c3433eacd2c659e41b5f17a3d10876ef
+NativeFormatImporter:
+  externalObjects: {}
+  mainObjectFileID: 11400000
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

My project/Assets/_Scripts/Editor.meta

+fileFormatVersion: 2
+guid: 852beafb6193f3b428c62d435119ed37
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

My project/Assets/_Scripts/Editor/EditorToolbarSceneButton.cs

+using UnityEditor;
+using UnityEditor.Toolbars;
+using UnityEditor.SceneManagement;
+using UnityEngine;
+
+/// <summary>
+/// Adds a "Scenes" button to the Unity main toolbar.
+/// Clicking it opens a flat "Main Scenes" menu populated from whichever
+/// EditorSceneCollection has "Show In Main Menu" enabled.
+/// </summary>
+public static class EditorToolbarSceneButton
+{
+    // ─── Toolbar Registration ────────────────────────────────────────────────
+
+    [MainToolbarElement("Scenes Button", defaultDockPosition = MainToolbarDockPosition.Right)]
+    public static MainToolbarElement GetScenesButton()
+    {
+        Texture2D icon = EditorGUIUtility.IconContent("SceneAsset Icon").image as Texture2D;
+
+        return new MainToolbarButton(
+            new MainToolbarContent("Scenes", icon, "Open a scene from Main Scenes."),
+            OnOpenScenesMenu
+        );
+    }
+
+    // ─── Menu Construction ───────────────────────────────────────────────────
+
+    private static void OnOpenScenesMenu()
+    {
+        GenericMenu menu = new GenericMenu();
+
+        EditorSceneCollection mainCollection = FindMainCollection();
+
+        if (mainCollection == null)
+        {
+            menu.AddDisabledItem(new GUIContent("No collection has 'Show In Main Menu' enabled."));
+            menu.ShowAsContext();
+            return;
+        }
+
+        // ── Header ──────────────────────────────────────────────────────────
+        menu.AddDisabledItem(new GUIContent("Main Scenes"));
+        menu.AddSeparator("");
+
+        // ── Optional description ─────────────────────────────────────────────
+        if (!string.IsNullOrWhiteSpace(mainCollection.Description))
+        {
+            menu.AddDisabledItem(new GUIContent(mainCollection.Description));
+            menu.AddSeparator("");
+        }
+
+        // ── Individual scenes ────────────────────────────────────────────────
+        bool anyScenesAdded = false;
+
+        if (mainCollection.SceneAssets != null)
+        {
+            foreach (SceneAsset scene in mainCollection.SceneAssets)
+            {
+                if (scene == null) continue;
+
+                string scenePath = AssetDatabase.GetAssetPath(scene);
+                string sceneName = scene.name;
+
+                menu.AddItem(new GUIContent(sceneName), false, () => OpenScene(scenePath));
+                anyScenesAdded = true;
+            }
+        }
+
+        if (!anyScenesAdded)
+            menu.AddDisabledItem(new GUIContent("No scenes assigned to this collection."));
+
+        // ── Open All shortcut ────────────────────────────────────────────────
+        menu.AddSeparator("");
+        menu.AddItem(new GUIContent("Open All"), false, mainCollection.OpenAll);
+
+        menu.ShowAsContext();
+    }
+
+    // ─── Helpers ─────────────────────────────────────────────────────────────
+
+    /// <summary>
+    /// Finds the first EditorSceneCollection with ShowInMainMenu enabled.
+    /// Logs a warning if more than one is found.
+    /// </summary>
+    private static EditorSceneCollection FindMainCollection()
+    {
+        string[] guids = AssetDatabase.FindAssets("t:EditorSceneCollection");
+
+        EditorSceneCollection result = null;
+        int mainCount = 0;
+
+        foreach (string guid in guids)
+        {
+            string path = AssetDatabase.GUIDToAssetPath(guid);
+            var collection = AssetDatabase.LoadAssetAtPath<EditorSceneCollection>(path);
+
+            if (collection == null || !collection.ShowInMainMenu) continue;
+
+            result ??= collection;
+            mainCount++;
+        }
+
+        if (mainCount > 1)
+            Debug.LogWarning("[EditorToolbarSceneButton] More than one EditorSceneCollection has 'Show In Main Menu' enabled. Only the first one found will be used.");
+
+        return result;
+    }
+
+    /// <summary>
+    /// Opens a single scene. Prompts the user to save unsaved changes first.
+    /// </summary>
+    private static void OpenScene(string path)
+    {
+        if (EditorSceneManager.SaveCurrentModifiedScenesIfUserWantsTo())
+            EditorSceneManager.OpenScene(path, OpenSceneMode.Single);
+    }
+}
\ No newline at end of file

My project/Assets/_Scripts/Editor/EditorToolbarSceneButton.cs.meta

+fileFormatVersion: 2
+guid: d4dab859724741b4dae4a37ec651b647
\ No newline at end of file

My project/Assets/_Scripts/ScriptableObject.meta

+fileFormatVersion: 2
+guid: 7d3de6a23d22fe64e815ebd43b20b2b7
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

My project/Assets/_Scripts/ScriptableObject/EditorSceneCollection.cs

+using UnityEditor;
+using UnityEditor.SceneManagement;
+using UnityEngine;
+
+/// <summary>
+/// A ScriptableObject that groups scenes you frequently open together.
+/// Create via: Assets > Create > Editor Tools > Scene Collection
+/// </summary>
+[CreateAssetMenu(fileName = "NewSceneCollection", menuName = "Editor Tools/Scene Collection")]
+public class EditorSceneCollection : ScriptableObject
+{
+    // ─── Inspector Fields ────────────────────────────────────────────────────
+
+    [Tooltip("Label shown in the toolbar menu. Falls back to the asset name if left empty.")]
+    [SerializeField] private string collectionName;
+
+    [Tooltip("Optional note shown as a disabled hint at the top of the menu.")]
+    [SerializeField] private string description;
+
+    [Tooltip("If enabled, this collection's scenes appear in the Main Scenes toolbar menu.\nOnly one collection should have this checked at a time.")]
+    [SerializeField] private bool showInMainMenu;
+
+    [Tooltip("Scenes in this collection. The first scene opens Single; the rest open Additive.")]
+    [SerializeField] private SceneAsset[] sceneAssets;
+
+    // ─── Public API ──────────────────────────────────────────────────────────
+
+    /// <summary>Display name used in the toolbar menu.</summary>
+    public string CollectionName =>
+        string.IsNullOrWhiteSpace(collectionName) ? name : collectionName;
+
+    /// <summary>Optional description shown as a disabled hint in the menu.</summary>
+    public string Description => description;
+
+    /// <summary>Whether this collection feeds the Main Scenes toolbar menu.</summary>
+    public bool ShowInMainMenu => showInMainMenu;
+
+    /// <summary>Read-only access to the scene assets in this collection.</summary>
+    public SceneAsset[] SceneAssets => sceneAssets;
+
+    /// <summary>
+    /// Opens all scenes in the collection.
+    /// The first scene replaces the current setup; the rest load additively.
+    /// Prompts the user to save any unsaved changes first.
+    /// </summary>
+    public void OpenAll()
+    {
+        if (sceneAssets == null || sceneAssets.Length == 0)
+        {
+            Debug.LogWarning($"[SceneCollection] '{CollectionName}' has no scenes assigned.");
+            return;
+        }
+
+        if (!EditorSceneManager.SaveCurrentModifiedScenesIfUserWantsTo())
+            return;
+
+        for (int i = 0; i < sceneAssets.Length; i++)
+        {
+            if (sceneAssets[i] == null) continue;
+
+            string path = AssetDatabase.GetAssetPath(sceneAssets[i]);
+            var mode = (i == 0) ? OpenSceneMode.Single : OpenSceneMode.Additive;
+            EditorSceneManager.OpenScene(path, mode);
+        }
+    }
+}
\ No newline at end of file

My project/Assets/_Scripts/ScriptableObject/EditorSceneCollection.cs.meta

+fileFormatVersion: 2
+guid: 9d12c215cf29fa446abc76913d213425
\ No newline at end of file

My project/ProjectSettings/ProjectVersion.txt

-m_EditorVersion: 6000.3.8f1
-m_EditorVersionWithRevision: 6000.3.8f1 (1c7db571dde0)
+m_EditorVersion: 6000.3.9f1
+m_EditorVersionWithRevision: 6000.3.9f1 (7a9955a4f2fa)