diff --git a/src/AutoCardSelector.cs b/src/AutoCardSelector.cs
new file mode 100644
index 0000000..6704590
--- /dev/null
+++ b/src/AutoCardSelector.cs
@@ -0,0 +1,31 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using MegaCrit.Sts2.Core.Entities.CardRewardAlternatives;
+using MegaCrit.Sts2.Core.Entities.Cards;
+using MegaCrit.Sts2.Core.Models;
+using MegaCrit.Sts2.Core.TestSupport;
+
+namespace StS2Sim;
+
+/// <summary>
+/// Card-select prompts (Armaments "pick a card to upgrade", Havoc "pick a card to play",
+/// etc.) need a selector or they NRE. The game's normal selector talks to a UI;
+/// for headless sims we just auto-pick the first <c>maxSelect</c> options
+/// (or skip if <c>minSelect == 0</c>).
+///
+/// This is a "good enough" heuristic — it doesn't try to make optimal choices.
+/// For decks with select-heavy cards we could swap in a smarter strategy later.
+/// </summary>
+internal sealed class AutoCardSelector : ICardSelector
+{
+    public Task<IEnumerable<CardModel>> GetSelectedCards(IEnumerable<CardModel> options, int minSelect, int maxSelect)
+    {
+        var list = options.ToList();
+        var picked = list.Take(System.Math.Max(minSelect, System.Math.Min(maxSelect, list.Count)));
+        return Task.FromResult<IEnumerable<CardModel>>(picked.ToList());
+    }
+
+    public CardModel? GetSelectedCardReward(IReadOnlyList<CardCreationResult> options, IReadOnlyList<CardRewardAlternative> alternatives)
+        => options.FirstOrDefault()?.Card;
+}
diff --git a/src/GodotShims.cs b/src/GodotShims.cs
index 436f86e..3b4fecd 100644
--- a/src/GodotShims.cs
+++ b/src/GodotShims.cs
@@ -46,6 +46,16 @@ internal static class GodotShims
             type: typeof(Godot.Time),
             methodName: "GetTicksMsec",
             prefix: typeof(GodotShims).GetMethod(nameof(Time_GetTicksMsec_Prefix), BindingFlags.Static | BindingFlags.NonPublic)!);
+
+        // CardPileCmd.Shuffle calls Engine.GetMainLoop() for animation pacing
+        // (sleeps between adding cards back to draw pile). We replace the whole
+        // method with a synchronous shuffle that does the same logical work
+        // without ever touching SceneTree.
+        PatchPrefix(
+            harmony,
+            type: typeof(MegaCrit.Sts2.Core.Commands.CardPileCmd),
+            methodName: "Shuffle",
+            prefix: typeof(GodotShims).GetMethod(nameof(CardPileCmd_Shuffle_Prefix), BindingFlags.Static | BindingFlags.NonPublic)!);
     }
 
     private static void PatchPrefix(Harmony harmony, Type? type, string methodName, MethodInfo prefix)
@@ -84,6 +94,57 @@ internal static class GodotShims
         return false;
     }
 
+    // Replacement for CardPileCmd.Shuffle that skips the per-card animation wait
+    // (which calls Engine.GetMainLoop() and crashes outside Godot). Logic mirrors
+    // the original: pull discards, shuffle by player's RNG, re-add to draw pile.
+    private static bool CardPileCmd_Shuffle_Prefix(
+        MegaCrit.Sts2.Core.GameActions.Multiplayer.PlayerChoiceContext choiceContext,
+        MegaCrit.Sts2.Core.Entities.Players.Player player,
+        ref System.Threading.Tasks.Task __result)
+    {
+        __result = ShuffleSync(player);
+        return false;
+    }
+
+    private static System.Threading.Tasks.Task ShuffleSync(MegaCrit.Sts2.Core.Entities.Players.Player player)
+    {
+        var pcs = player.PlayerCombatState;
+        if (pcs == null) return System.Threading.Tasks.Task.CompletedTask;
+
+        var draw = pcs.DrawPile;
+        var discard = pcs.DiscardPile;
+        var combined = new System.Collections.Generic.List<MegaCrit.Sts2.Core.Models.CardModel>(discard.Cards);
+
+        var inDraw = new System.Collections.Generic.HashSet<MegaCrit.Sts2.Core.Models.CardModel>(draw.Cards);
+        foreach (var c in inDraw)
+        {
+            draw.RemoveInternal(c, silent: true);
+            combined.Add(c);
+        }
+
+        // Fisher-Yates with the player's shuffle RNG. Sufficient for our purposes —
+        // the game's StableShuffle has tie-breaking semantics for IComparable<T>
+        // that CardModel doesn't satisfy, but card identity isn't tied here.
+        var rng = player.RunState.Rng.Shuffle;
+        for (int i = combined.Count - 1; i > 0; i--)
+        {
+            int j = rng.NextInt(0, i + 1);
+            (combined[i], combined[j]) = (combined[j], combined[i]);
+        }
+
+        // Re-add to draw pile (we drop the per-card wait because it's animation-only).
+        foreach (var c in combined)
+        {
+            if (inDraw.Contains(c)) draw.AddInternal(c, -1, silent: true);
+            else
+            {
+                discard.RemoveInternal(c, silent: true);
+                draw.AddInternal(c, -1, silent: true);
+            }
+        }
+        return System.Threading.Tasks.Task.CompletedTask;
+    }
+
     // Localization isn't initialized in headless mode, so Creature.ToString() (which
     // hits LocString.GetFormattedText()) throws. Patch it to return a safe identifier.
     public static void ApplyLocalizationShim()
diff --git a/src/Harness.cs b/src/Harness.cs
index 84c530f..0ff0431 100644
--- a/src/Harness.cs
+++ b/src/Harness.cs
@@ -42,6 +42,10 @@ internal static class Harness
         ModelDb.InitIds();
 
         GodotShims.ApplyLocalizationShim();
+
+        // Cards like Armaments ("pick a card to upgrade") wait for a CardSelectCmd
+        // selector. Without one, they NRE. Register a global auto-picker.
+        MegaCrit.Sts2.Core.Commands.CardSelectCmd.UseSelector(new AutoCardSelector());
     }
 
     public sealed class CombatHarness
diff --git a/src/SimServer.cs b/src/SimServer.cs
index fbcb367..a6894b3 100644
--- a/src/SimServer.cs
+++ b/src/SimServer.cs
@@ -253,7 +253,8 @@ internal sealed class SimServer
             }
             catch (Exception ex)
             {
-                await BroadcastEvent(new { type = "error", message = ex.Message });
+                Console.Error.WriteLine("[SimServer] sim run threw:\n" + ex);
+                await BroadcastEvent(new { type = "error", message = ex.Message, stack = ex.ToString() });
             }
         }, ct);
     }