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/ExecutableMainEventChainTests.cs

@@ -0,0 +1,50 @@
+namespace Cthangover.Mods.Dialog.Tests
+{
+    using System.Threading.Tasks;
+    using Cthangover.Core.Mods.Testing;
+    using Cthangover.Core.Scenes;
+    using Cthangover.Mods.Dialog.Executable;
+
+    /// <summary>
+    /// <see cref="ExecutableMainEventChain"/> is event-driven and loop-safe: the next
+    /// event starts within a couple of frames after a dialog ends (no polling delay),
+    /// two repeatable events do not ping-pong while the state stays the same, and a
+    /// state change makes them eligible again.
+    /// </summary>
+    public class ExecutableMainEventChainTests
+    {
+        [ModTest("chain/push_start_and_no_ping_pong", TimeoutSeconds = 15)]
+        static async Task PushStartAndNoPingPong(ModTestContext ctx)
+        {
+            var stage = await DialogStage.Create();
+            try
+            {
+                var chain = new ExecutableMainEventChain { Name = "TestChain" };
+                stage.Host.AddChild(chain);
+                var a = new ScenarioEvent { ScenarioText = "text \"A\"", ScenarioId = "dialog_base_test_chain_a" };
+                var b = new ScenarioEvent { ScenarioText = "text \"B\"", ScenarioId = "dialog_base_test_chain_b" };
+                chain.AddEvent(a);
+                chain.AddEvent(b);
+
+                await DialogStage.Frames(2);
+                ModAssert.True(stage.Box.Locker == a, "first event starts right after it was added");
+
+                stage.Box.NextAction();
+                await DialogStage.Frames(2);
+                ModAssert.True(stage.Box.Locker == b, "second event starts within two frames after the first ended");
+
+                stage.Box.NextAction();
+                await DialogStage.Frames(4);
+                ModAssert.False(stage.Box.IsRunning, "no event re-runs while the state did not change");
+
+                ConditionStateMonitor.MarkStateChanged();
+                await DialogStage.Frames(2);
+                ModAssert.True(stage.Box.Locker == a, "a state change makes the first event eligible again");
+            }
+            finally
+            {
+                stage.Free();
+            }
+        }
+    }
+}