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/StoryFlagTests.cs

@@ -0,0 +1,42 @@
+namespace Cthangover.Mods.Dialog.Tests
+{
+    using System.Threading.Tasks;
+    using Cthangover.Core.Mods.Testing;
+    using Cthangover.Core.Scenes;
+    using Cthangover.Core.Settings;
+    using Cthangover.Mods.Dialog.Scenarios;
+
+    /// <summary>
+    /// The scenario <c>flag</c> command sets a story flag of the game: once the
+    /// dialog reaches it, scenario conditions see the value, the game state
+    /// holds it (so saves carry it), and conditions are rescanned.
+    /// </summary>
+    public class StoryFlagTests
+    {
+        private const string Flag = "__test_story_flag";
+
+        [ModTest("flags/flag_command_sets_game_flag", TimeoutSeconds = 10)]
+        static async Task FlagCommandSetsGameFlag(ModTestContext ctx)
+        {
+            var stage = await DialogStage.Create();
+            var flags = GameData.Instance.Runtime.Flags;
+            try
+            {
+                var dlg = new ScenarioConverter().Convert($"flag {Flag} open\nend\n");
+                var versionBefore = ConditionStateMonitor.Version;
+
+                ModAssert.False(ScenarioCondition.Evaluate($"{Flag} == \"open\""), "condition false before the dialog");
+                ModAssert.True(stage.Box.SetDialogQueueAndRun(dlg, null, 0, null), "dialog starts");
+
+                ModAssert.True(ScenarioCondition.Evaluate($"{Flag} == \"open\""), "condition sees the flag");
+                ModAssert.Equal("open", flags.TryGetValue(Flag, out var value) ? value : null, "game state holds the flag");
+                ModAssert.True(ConditionStateMonitor.Version > versionBefore, "conditions are rescanned");
+            }
+            finally
+            {
+                flags.Remove(Flag);
+                stage.Free();
+            }
+        }
+    }
+}