diff --git a/manifest.json b/manifest.json
index e6af884..ba8411e 100644
--- a/manifest.json
+++ b/manifest.json
@@ -13,6 +13,7 @@
     {"id": "menu_flow", "activate": ["--itest=menu_flow"]},
     {"id": "save_dormancy", "activate": ["--itest=save_dormancy"]},
     {"id": "new_game", "activate": ["--itest=new_game"]},
-    {"id": "hot_reload", "activate": ["--itest=hot_reload"]}
+    {"id": "hot_reload", "activate": ["--itest=hot_reload"]},
+    {"id": "collection_edit", "activate": ["--itest=collection_edit"]}
   ]
 }
diff --git a/src/GameFlow.cs b/src/GameFlow.cs
index 2c3719d..fa23d84 100644
--- a/src/GameFlow.cs
+++ b/src/GameFlow.cs
@@ -92,8 +92,13 @@ namespace Cthangover.BaseMenu
                 ReloadRequired = false;
         }
 
+        /// <summary>
+        /// The game is loaded and still matches its collection — only then can it
+        /// be entered without a mod-set switch (an edited collection must apply).
+        /// </summary>
         private static bool IsRunning(string gameId)
-            => ActiveGame.IsActive && string.Equals(ActiveGame.Id, gameId, StringComparison.OrdinalIgnoreCase);
+            => ActiveGame.IsActive && string.Equals(ActiveGame.Id, gameId, StringComparison.OrdinalIgnoreCase)
+               && !GameCatalog.IsActiveOutdated();
 
         /// <summary>Lists what a composition change does to the save, in player terms.</summary>
         public static string DescribeDiff(SaveCompositionDiff diff)
diff --git a/test_suites/collection_edit/manifest.json b/test_suites/collection_edit/manifest.json
new file mode 100644
index 0000000..d0bef49
--- /dev/null
+++ b/test_suites/collection_edit/manifest.json
@@ -0,0 +1,7 @@
+{
+  "name": "Collection Edit Test",
+  "description": "Integration test of editing the running game's collection: the novel template is entered, its collection gets the editors mechanic, back to the menu and New game of the same game must switch the mod set in-process so the editors are loaded. Activated only by --itest=collection_edit (with --game=novel_template).",
+  "sources": [
+    "src/*.cs"
+  ]
+}
diff --git a/test_suites/collection_edit/src/CollectionEditTestDriverNode.cs b/test_suites/collection_edit/src/CollectionEditTestDriverNode.cs
new file mode 100644
index 0000000..592658d
--- /dev/null
+++ b/test_suites/collection_edit/src/CollectionEditTestDriverNode.cs
@@ -0,0 +1,259 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.Json;
+using Cthangover.Core.Bootstrap;
+using Cthangover.Core.Events;
+using Cthangover.Core.Games;
+using Cthangover.Core.Mods;
+using Cthangover.Core.Mods.HotReload;
+using Cthangover.Core.Scenes;
+using Cthangover.Core.Utils;
+using Godot;
+
+namespace Mods.CollectionEditTest
+{
+    /// <summary>
+    /// The player edits the collection of the game that is running, in ONE process:
+    /// <list type="number">
+    /// <item>The novel template is entered; it matches its collection and the
+    /// editors are not loaded.</item>
+    /// <item>The collection gets the editors mechanic (<c>editor_tools</c>), saved
+    /// the way the collection editor saves it (a user package with the same id):
+    /// the running game is now outdated.</item>
+    /// <item>Menu → Play → New game of the same game switches the mod set in
+    /// place: the editors are loaded and the game matches its collection again.</item>
+    /// </list>
+    /// A player's own package of the game is moved aside for the run and put
+    /// back afterwards. Prints <c>[TEST_RESULT] name=collection_edit</c>.
+    /// </summary>
+    public partial class CollectionEditTestDriverNode : Node
+    {
+        public const string Flag = "--itest=collection_edit";
+
+        private const string GameId = "novel_template";
+        private const string AddedMod = "editor_tools";
+        private const float TimeoutSeconds = 240f;
+
+        private readonly List<string> failures = new();
+        private readonly List<string> enteredScenes = new();
+        private readonly List<(string From, string To)> movedAside = new();
+        private int passed;
+        private int step;
+        private double elapsed;
+        private double stepAt;
+        private bool done;
+
+        public override void _Ready()
+        {
+            // The driver must keep ticking across the mod-set switch.
+            ProcessMode = ProcessModeEnum.Always;
+            ModEventBus.Subscribe<SceneEnteredEvent>(OnSceneEntered);
+        }
+
+        public override void _ExitTree()
+        {
+            ModEventBus.Unsubscribe<SceneEnteredEvent>(OnSceneEntered);
+        }
+
+        public override void _Process(double delta)
+        {
+            if (done)
+                return;
+
+            elapsed += delta;
+            if (elapsed > TimeoutSeconds)
+            {
+                failures.Add($"timeout at step {step} (scene='{SceneManager.GetCurrentSceneName()}', game='{ActiveGame.Id}')");
+                Finish();
+                return;
+            }
+
+            if (elapsed - stepAt < 0.25)
+                return;
+            stepAt = elapsed;
+
+            try
+            {
+                RunStep();
+            }
+            catch (Exception ex)
+            {
+                failures.Add($"step {step}: {ex.GetType().Name}: {ex.Message}");
+                Finish();
+            }
+        }
+
+        private Control Menu => GetTree().CurrentScene as Control;
+
+        private static bool Busy => GameSession.IsSwitching || ModManager.Instance.IsReloading || ModHotReloadService.IsReloadRunning;
+
+        private static bool EditorsLoaded => ModRegistry.Instance.Mods.ContainsKey(AddedMod);
+
+        /// <summary>Scenes of the game entered since the last clear; the main menu does not count.</summary>
+        private void OnSceneEntered(SceneEnteredEvent e)
+        {
+            if (!string.Equals(e.SceneName, "mainmenu", StringComparison.OrdinalIgnoreCase))
+                enteredScenes.Add(e.SceneName);
+        }
+
+        private void RunStep()
+        {
+            switch (step)
+            {
+                case 0:
+                    if (!Boot.IsReady || Busy || ActiveGame.Id != GameId || enteredScenes.Count == 0)
+                        return;
+                    Check($"game '{GameId}' entered ('{enteredScenes[0]}')", true);
+                    Check("a freshly entered game matches its collection", !GameCatalog.IsActiveOutdated());
+                    Check($"'{AddedMod}' is not loaded before the edit", !EditorsLoaded);
+
+                    AddEditorsToCollection();
+                    Check("the edited collection makes the running game outdated", GameCatalog.IsActiveOutdated());
+                    GetTree().Root.GetNode<GodotSceneService>("GodotSceneService").SwitchToMenu();
+                    break;
+
+                case 1:
+                    if (Busy || !PressMenuPlay())
+                        return;
+                    enteredScenes.Clear();
+                    break;
+
+                case 2:
+                    if (!StartFromPicker())
+                        return;
+                    break;
+
+                case 3:
+                {
+                    if (Busy || ActiveGame.Id != GameId || enteredScenes.Count == 0)
+                        return;
+                    var reload = ModManager.Instance.LastReload;
+                    Check("New game after the edit switched the mod set", reload?.Applied == true && reload.Plan?.Load.Contains(AddedMod) == true);
+                    Check($"'{AddedMod}' is loaded after the edit", EditorsLoaded);
+                    Check("the game matches its edited collection", !GameCatalog.IsActiveOutdated());
+                    Check($"entered a scene of '{GameId}' ('{enteredScenes[0]}')", true);
+                    Finish();
+                    return;
+                }
+            }
+
+            step++;
+        }
+
+        /// <summary>
+        /// Saves the game's collection with an extra editors mechanic as a user
+        /// package — what the collection editor does when the player adds one.
+        /// </summary>
+        private void AddEditorsToCollection()
+        {
+            MoveUserPackageAside();
+            var source = GameCatalog.LoadCollections()[GameId];
+            var edited = JsonSerializer.Deserialize<ModCollection>(JsonSerializer.Serialize(source));
+            edited.Package = source.Package;
+            edited.Mechanics ??= new List<ModCollectionMechanic>();
+            edited.Mechanics.Add(new ModCollectionMechanic { Id = "editors", Name = "Editors", Mods = new List<string> { AddedMod + ">=1" } });
+
+            var user = ModCollectionStore.LoadUser().Where(c => !string.Equals(c.Id, GameId, StringComparison.OrdinalIgnoreCase)).ToList();
+            user.Add(edited);
+            ModCollectionStore.SaveUser(user);
+        }
+
+        private void MoveUserPackageAside()
+        {
+            var root = ModCollectionStore.UserPath;
+            foreach (var path in new[] { Path.Combine(root, GameId), Path.Combine(root, GameId + ".zip") })
+            {
+                var aside = Path.Combine(Path.GetDirectoryName(root) ?? root, $"collection_edit_backup_{Path.GetFileName(path)}");
+                if (Directory.Exists(path))
+                    Directory.Move(path, aside);
+                else if (File.Exists(path))
+                    File.Move(path, aside);
+                else
+                    continue;
+                movedAside.Add((path, aside));
+            }
+        }
+
+        private void Cleanup()
+        {
+            ModCollectionStore.RemoveUser(GameId);
+            foreach (var (from, aside) in movedAside)
+            {
+                if (Directory.Exists(aside))
+                    Directory.Move(aside, from);
+                else if (File.Exists(aside))
+                    File.Move(aside, from);
+            }
+        }
+
+        /// <summary>The main menu's Play button, pressed; false while it is not on screen.</summary>
+        private bool PressMenuPlay()
+        {
+            if (Menu?.FindChild("play", true, false) is not Button play)
+                return false;
+            play.EmitSignal(BaseButton.SignalName.Pressed);
+            return true;
+        }
+
+        /// <summary>Presses New game on the game's card in the picker; false until the picker is open.</summary>
+        private bool StartFromPicker()
+        {
+            var picker = Menu?.FindChild("GamePickerPanel", true, false) as Control;
+            if (picker?.Visible != true)
+                return false;
+            var game = GameCatalog.Games().FirstOrDefault(g => g.Collection.Id == GameId);
+            var start = StartButton(picker, game?.Name ?? GameId);
+            Check($"'{GameId}' card has an enabled New game button", start is { Disabled: false });
+            if (start == null || start.Disabled)
+            {
+                Finish();
+                return false;
+            }
+
+            start.EmitSignal(BaseButton.SignalName.Pressed);
+            return true;
+        }
+
+        /// <summary>The New game button on the card titled <paramref name="title"/>.</summary>
+        private static Button StartButton(Node picker, string title)
+        {
+            var newGameText = TranslationServer.Translate("menu/play/new_game").ToString();
+            // A card is the innermost panel holding exactly one New game button (the picker frame holds them all).
+            foreach (var card in picker.FindChildren("*", "PanelContainer", true, false))
+            {
+                var starts = card.FindChildren("*", "Button", true, false).OfType<Button>().Where(b => b.Text == newGameText).ToList();
+                if (starts.Count == 1 && card.FindChildren("*", "Label", true, false).OfType<Label>().Any(l => l.Text == title))
+                    return starts[0];
+            }
+            return null;
+        }
+
+        private void Check(string name, bool ok)
+        {
+            if (ok)
+            {
+                passed++;
+                GameLogger.Log("TEST", $"CollectionEditTest: [OK] {name}");
+            }
+            else
+            {
+                failures.Add(name);
+                GameLogger.Log("TEST", $"CollectionEditTest: [FAIL] {name}", LogLevel.Error);
+            }
+        }
+
+        private void Finish()
+        {
+            if (done)
+                return;
+            done = true;
+            Cleanup();
+            foreach (var failure in failures)
+                GameLogger.Log("TEST", $"CollectionEditTest: failed: {failure}");
+            GameLogger.Log("TEST", $"[TEST_RESULT] name=collection_edit passed={passed} failed={failures.Count}");
+            GetTree().Quit(failures.Count == 0 ? 0 : 1);
+        }
+    }
+}
diff --git a/test_suites/collection_edit/src/CollectionEditTestInitializer.cs b/test_suites/collection_edit/src/CollectionEditTestInitializer.cs
new file mode 100644
index 0000000..7bb2bac
--- /dev/null
+++ b/test_suites/collection_edit/src/CollectionEditTestInitializer.cs
@@ -0,0 +1,25 @@
+using System.Linq;
+using Cthangover.Core.Mods;
+using Cthangover.Core.Utils;
+using Godot;
+
+namespace Mods.CollectionEditTest
+{
+    /// <summary>Queues <see cref="CollectionEditTestDriverNode"/> only for <c>--itest=collection_edit</c>.</summary>
+    public class CollectionEditTestInitializer : IModInitializer
+    {
+        private static bool queued;
+
+        public void OnModLoaded(string modId) { }
+
+        public void OnModResourcesReady()
+        {
+            if (queued || !OS.GetCmdlineUserArgs().Contains(CollectionEditTestDriverNode.Flag))
+                return;
+
+            queued = true;
+            GameLogger.Log("TEST", "CollectionEditTest: activating");
+            (Godot.Engine.GetMainLoop() as SceneTree)?.Root?.CallDeferred("add_child", new CollectionEditTestDriverNode());
+        }
+    }
+}