diff --git a/SVSim.BattleEngine.Tests/SessionEngine/SessionEngineSpellboostTests.cs b/SVSim.BattleEngine.Tests/SessionEngine/SessionEngineSpellboostTests.cs
index 4233c67..bad88f1 100644
--- a/SVSim.BattleEngine.Tests/SessionEngine/SessionEngineSpellboostTests.cs
+++ b/SVSim.BattleEngine.Tests/SessionEngine/SessionEngineSpellboostTests.cs
@@ -1,6 +1,7 @@
 using NUnit.Framework;
 using SVSim.BattleNode.Sessions.Engine;
 using System.Linq;
+using SVSim.BattleEngine.Tests;
 
 namespace SVSim.BattleEngine.Tests.SessionEngine;
 
@@ -15,6 +16,10 @@ public class SessionEngineSpellboostTests
         var cl2 = CaptureReplay.Load("battle_test_cl2.ndjson");
         var deckA = CaptureReplay.SelfDeckFrom(cl1);
         var deckB = CaptureReplay.SelfDeckFrom(cl2);
+        // Belt-and-suspenders (matches the sibling tests): load the decks into the harness master so
+        // this test never depends on global card-master contents. EnsureInitialized() above still
+        // proves EngineGlobalInit's own path works.
+        foreach (var id in deckA.Concat(deckB).Distinct()) HeadlessCardMaster.Load((int)id);
         var engine = new SessionBattleEngine();
         Assert.DoesNotThrow(() => engine.Setup(masterSeed: 12345, seatADeck: deckA, seatBDeck: deckB));
         Assert.That(engine.IsReady, Is.True, "engine must be ready after EngineGlobalInit (carried-risk fix)");
diff --git a/SVSim.BattleNode/Sessions/Engine/EngineGlobalInit.cs b/SVSim.BattleNode/Sessions/Engine/EngineGlobalInit.cs
index 6f386c8..b9b08ec 100644
--- a/SVSim.BattleNode/Sessions/Engine/EngineGlobalInit.cs
+++ b/SVSim.BattleNode/Sessions/Engine/EngineGlobalInit.cs
@@ -34,8 +34,11 @@ namespace SVSim.BattleNode.Sessions.Engine;
 /// <c>HeadlessCardMaster</c> + <c>HeadlessMasterData</c>; the reflection seams are transcribed verbatim.
 /// It differs in exactly three ways: (1) it loads the FULL cards.json (every row, no id filter) since
 /// the live host serves arbitrary decks; (2) it installs ALL 8 classes in ClassCharacterList; and
-/// (3) every set is guarded so the call is idempotent AND does not fight the test
-/// <c>HeadlessEngineEnv</c> if both run in one NUnit process.</summary>
+/// (3) the call is idempotent (process-once via <c>_done</c>). Coexistence: it does not OVERWRITE
+/// harmless globals another initializer set (<c>Data.Load</c>, <c>Crossover</c>, leader chara ids,
+/// netUser, udid are all set-only-if-absent), but it ALWAYS guarantees the postcondition — the FULL
+/// card master and the all-8-class Master — by rebuilding/re-injecting both unconditionally rather
+/// than deferring to a possibly-thinner existing global (e.g. a test harness's single-card master).</summary>
 internal static class EngineGlobalInit
 {
     private static readonly object _gate = new();
@@ -74,16 +77,19 @@ internal static class EngineGlobalInit
             BattleManagerBase.IsForecast = true;
 
             // --- static CardMaster (full cards.json) ----------------------------------------------
-            // Skip the (expensive) full load if a CardMaster is already registered as Default — a
-            // prior EngineGlobalInit call OR a HeadlessEngineEnv/HeadlessCardMaster load in the same
-            // NUnit process already populated it.
-            if (!IsCardMasterPopulated())
-                LoadFullCardMaster();
+            // ALWAYS rebuild + re-inject the FULL master. We must not defer to a possibly-thin
+            // existing Default (e.g. a HeadlessCardMaster.Load(singleCard) from an earlier test in
+            // the same NUnit process): the postcondition is the COMPLETE card master, and a thin
+            // master makes Setup→SeedDeck NRE in SkillCreator.CreateBuildInfo. EnsureInitialized is
+            // process-once via _done, so an unconditional load runs at most once — the skip-
+            // optimization bought nothing and traded correctness for a coexistence hazard.
+            // LoadFullCardMaster rebuilds + re-injects Default, so it's idempotent.
+            LoadFullCardMaster();
 
             // --- Master reference data (all 8 classes' chara list) ---------------------------------
-            // Skip if Data.Master is already non-null with a non-empty ClassCharacterList.
-            if (!IsMasterPopulated())
-                InstallMaster();
+            // ALWAYS install all 8 classes. Don't defer to a prior (e.g. 2-class) harness master:
+            // the postcondition is all-8-class ClassCharacterList. Idempotent (replaces Data.Master).
+            InstallMaster();
 
             // --- GameMgr DataMgr leader chara ids --------------------------------------------------
             // Set the backing fields directly: the public SetPlayerCharaId() also pulls MyRotation/
@@ -111,11 +117,12 @@ internal static class EngineGlobalInit
             // --- Cute.Certification.udid -----------------------------------------------------------
             // The emit-path payload builder reads Certification.Udid, whose getter lazily decodes from
             // Toolbox.SavedataManager (null headless). Seed the private static backing field with a
-            // non-empty placeholder so the getter short-circuits. Only set when empty (coexistence).
+            // non-empty placeholder (opaque — only echoed, never matched) so the getter short-
+            // circuits. Matches the harness value. Only set when empty (coexistence).
             var udidField = typeof(Certification).GetField("udid",
                 BindingFlags.Static | BindingFlags.NonPublic)!;
             if (string.IsNullOrEmpty(udidField.GetValue(null) as string))
-                udidField.SetValue(null, "host-udid");
+                udidField.SetValue(null, "headless-udid");
 
             _done = true;
         }
@@ -123,16 +130,6 @@ internal static class EngineGlobalInit
 
     // --- CardMaster (full load) ----------------------------------------------------------------------
 
-    private static bool IsCardMasterPopulated()
-    {
-        var idType = typeof(CardMaster).GetNestedType("CardMasterId")!;
-        var defaultId = Enum.Parse(idType, "Default");
-        var fld = typeof(CardMaster).GetField("_dictCardMaster",
-            BindingFlags.Static | BindingFlags.NonPublic)!;
-        if (fld.GetValue(null) is not IDictionary dict) return false;
-        return dict.Contains(defaultId) && dict[defaultId] != null;
-    }
-
     // Production difference (1): enumerate EVERY card row — no want.Contains(id) filter.
     private static void LoadFullCardMaster()
     {
@@ -201,14 +198,6 @@ internal static class EngineGlobalInit
 
     // --- Master reference data (all 8 classes) -------------------------------------------------------
 
-    private static bool IsMasterPopulated()
-    {
-        if (Data.Master is not Master m) return false;
-        var p = typeof(Master).GetProperty("ClassCharacterList",
-            BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
-        return p?.GetValue(m) is ICollection { Count: > 0 };
-    }
-
     // Transcribed from HeadlessMasterData.Install. Production difference (2): install ALL 8 classes.
     private static void InstallMaster()
     {