diff --git a/src/api/ApplyPlayerActionRoute.cs b/src/api/ApplyPlayerActionRoute.cs
index 914fbd4d..7f8ae62b 100644
--- a/src/api/ApplyPlayerActionRoute.cs
+++ b/src/api/ApplyPlayerActionRoute.cs
@@ -3,6 +3,7 @@
 using Lib.OS;
 using Microsoft.AspNetCore.Http.HttpResults;
 using UfoGameLib.Controller;
+using UfoGameLib.Events;
 using UfoGameLib.Lib;
 using UfoGameLib.State;
 
@@ -46,7 +47,7 @@ private static JsonHttpResult<GameSessionTurn> ApplyPlayerActionInternal(
         var controller = new GameSessionController(config, log, gameSession);
 
         // kja2-assert: make this check stronger, for membership in valid action name. See https://chatgpt.com/c/fb0a4197-4397-4f3f-bc13-2e0468141b0b        
-        Contract.Assert(playerActionPayload.ActionName != "AdvanceTimePlayerAction");
+        Contract.Assert(playerActionPayload.ActionName != GameEventName.AdvanceTimePlayerAction);
 
         gameSession.CurrentPlayerActionEvents.Add(playerActionPayload.Apply(controller));
         // See analogous line in UfoGameLib.Controller.GameSessionController.PlayGameUntilOver
diff --git a/src/api/PlayerActionPayload.cs b/src/api/PlayerActionPayload.cs
index 631862e8..2d82df73 100644
--- a/src/api/PlayerActionPayload.cs
+++ b/src/api/PlayerActionPayload.cs
@@ -41,7 +41,7 @@ private Func<PlayerActionEvent> TranslatePlayerActionToControllerAction(GameSess
         // https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns#positional-pattern
         => ActionName switch
         {
-            "AdvanceTimePlayerAction" => controller.AdvanceTimeNoWorldEvents,
+            EventNames.AdvanceTimePlayerAction => controller.AdvanceTimeNoWorldEvents,
             nameof(BuyTransportCapacityPlayerAction) => () => controller.CurrentTurnController.BuyTransportCapacity(TargetId!.Value),
             nameof(HireAgentsPlayerAction) => () => controller.CurrentTurnController.HireAgents(TargetId!.Value),
             nameof(SackAgentsPlayerAction) => () => controller.CurrentTurnController.SackAgents(Ids!),
diff --git a/src/game-lib/Controller/TimeAdvancementController.cs b/src/game-lib/Controller/TimeAdvancementController.cs
index df289e55..ee49db3c 100644
--- a/src/game-lib/Controller/TimeAdvancementController.cs
+++ b/src/game-lib/Controller/TimeAdvancementController.cs
@@ -33,7 +33,7 @@ public TimeAdvancementController(ILog log, RandomGen randomGen, EventIdGen event
 
         PlayerActionEvent advanceTimeEvent = new PlayerActionEvent(
             _eventIdGen.Generate,
-            "AdvanceTimePlayerAction",
+            GameEventName.AdvanceTimePlayerAction,
             targetId: state.Timeline.CurrentTurn);
 
         // Agents cost upkeep. Note we compute upkeep before evaluating missions.
@@ -200,7 +200,8 @@ private int UpdateActiveMissionSites(GameState state)
                 if (expired)
                 {
                     expiredMissions++;
-                    _worldEvents.Add(new MissionSiteExpiredEvent(_eventIdGen.Generate, missionSite.Id));
+                    _worldEvents.Add(
+                        new WorldEvent(_eventIdGen.Generate, GameEventName.MissionSiteExpiredEvent, missionSite.Id));
                     _log.Info($"{missionSite.LogString} expired!");
                 }
             }
diff --git a/src/game-lib/Events/GameEventName.cs b/src/game-lib/Events/GameEventName.cs
new file mode 100644
index 00000000..26c48e7c
--- /dev/null
+++ b/src/game-lib/Events/GameEventName.cs
@@ -0,0 +1,7 @@
+namespace UfoGameLib.Events;
+
+public static class GameEventName
+{
+    public const string AdvanceTimePlayerAction = "AdvanceTimePlayerAction";
+    public const string WorldEvent = "WorldEvent";
+}
diff --git a/src/game-lib/Events/MissionSiteExpiredEvent.cs b/src/game-lib/Events/MissionSiteExpiredEvent.cs
deleted file mode 100644
index 227fc017..00000000
--- a/src/game-lib/Events/MissionSiteExpiredEvent.cs
+++ /dev/null
@@ -1,16 +0,0 @@
-// ReSharper disable MemberCanBePrivate.Global
-// Reason: public fields are being serialized to JSON.
-namespace UfoGameLib.Events;
-
-public class MissionSiteExpiredEvent : WorldEvent
-{
-    public readonly int TargetId;
-
-    public MissionSiteExpiredEvent(int id, int targetId) : base(id, nameof(MissionSiteExpiredEvent))
-    {
-        TargetId = targetId;
-    }
-
-    public override MissionSiteExpiredEvent Clone()
-        => new(Id, TargetId);
-}
\ No newline at end of file
diff --git a/src/game-lib/Events/WorldEvent.cs b/src/game-lib/Events/WorldEvent.cs
index 540c4e0e..c1cfc629 100644
--- a/src/game-lib/Events/WorldEvent.cs
+++ b/src/game-lib/Events/WorldEvent.cs
@@ -2,13 +2,15 @@
 
 namespace UfoGameLib.Events;
 
-[JsonDerivedType(typeof(MissionSiteExpiredEvent))]
 public class WorldEvent : GameEvent
 {
-    public WorldEvent(int id, string type) : base(id, type)
+    public readonly int TargetId;
+
+    public WorldEvent(int id, string type, int targetId) : base(id, type)
     {
+        TargetId = targetId;    
     }
 
     public override WorldEvent Clone()
-        => new(Id, Type);
+        => new(Id, Type, TargetId);
 }
diff --git a/web/src/lib/codesync/WorldEvent.ts b/web/src/lib/codesync/WorldEvent.ts
index cb0e01d4..7a529181 100644
--- a/web/src/lib/codesync/WorldEvent.ts
+++ b/web/src/lib/codesync/WorldEvent.ts
@@ -1,9 +1,8 @@
 // codesync: UfoGameLib.Events.WorldEvent
 import type { GameEventBase } from './GameEvent'
 
-export type WorldEvent = MissionSiteExpiredEvent
-
-export type MissionSiteExpiredEvent = GameEventBase & {
+export type WorldEvent = GameEventBase & {
   readonly TargetId: number
 }
+
 export type WorldEventName = 'MissionSiteExpiredEvent'
diff --git a/web/src/lib/rendering/renderGameEvent.ts b/web/src/lib/rendering/renderGameEvent.ts
index 539f8baf..a0397e76 100644
--- a/web/src/lib/rendering/renderGameEvent.ts
+++ b/web/src/lib/rendering/renderGameEvent.ts
@@ -68,7 +68,7 @@ export function getDisplayedDetails(event: GameEventWithTurn): string {
   return formatString(
     playerActionNameToDisplayMap[event.Type as PlayerActionName]
       .displayedDetails,
-    event.Ids,
+    'Ids' in event ? event.Ids : undefined,
     event.TargetId,
   )
 }