Event-driven dialog queue, story flag command, mod unit tests

Push-based event chains, runtime fixes (single end, goto lifecycle, if,
busy box, held delay, empty options, timed/animated/effect actions), the
'flag name value' DSL command, autoplay --dialogs=N, 19 mod unit tests.

tests/DialogEndRecorder.cs

@@ -0,0 +1,33 @@
+namespace Cthangover.Mods.Dialog.Tests
+{
+    using System.Collections.Generic;
+    using Cthangover.Core.Events;
+
+    /// <summary>
+    /// Records every <see cref="DialogEndedEvent"/> published on the mod event bus
+    /// between <see cref="Start"/> and <see cref="Stop"/> — the locker id of each, in
+    /// publication order. Tests count how often a queue reported its end.
+    /// </summary>
+    public class DialogEndRecorder
+    {
+        /// <summary>Locker ids of the recorded events (null for a locker-less dialog).</summary>
+        public List<string> LockerIds { get; } = new();
+
+        /// <summary>Subscribes to the event bus.</summary>
+        public void Start()
+        {
+            ModEventBus.Subscribe<DialogEndedEvent>(OnDialogEnded);
+        }
+
+        /// <summary>Unsubscribes; call it in <c>finally</c> so a failed test leaves no handler behind.</summary>
+        public void Stop()
+        {
+            ModEventBus.Unsubscribe<DialogEndedEvent>(OnDialogEnded);
+        }
+
+        private void OnDialogEnded(DialogEndedEvent evt)
+        {
+            LockerIds.Add(evt.LockerId);
+        }
+    }
+}