diff --git a/SVSim.BattleNode/Bridge/MatchingBridge.cs b/SVSim.BattleNode/Bridge/MatchingBridge.cs
index b1940b8..2d4e419 100644
--- a/SVSim.BattleNode/Bridge/MatchingBridge.cs
+++ b/SVSim.BattleNode/Bridge/MatchingBridge.cs
@@ -1,3 +1,4 @@
+using System.Security.Cryptography;
 using SVSim.BattleNode.Sessions;
 
 namespace SVSim.BattleNode.Bridge;
@@ -23,8 +24,13 @@ public sealed class MatchingBridge : IMatchingBridge
     public PendingMatch RegisterPendingBattle(long viewerId)
     {
         // 12-digit decimal battle id mirrors the captures (e.g. "975695075012").
-        // Cast to long before Math.Abs to avoid OverflowException on int.MinValue.
-        var battleId = (Math.Abs((long)Guid.NewGuid().GetHashCode()) % 1_000_000_000_000L).ToString("D12");
+        // Two unbiased 6-digit draws concatenated — RandomNumberGenerator.GetInt32 uses
+        // rejection sampling so the result is uniform on [0, 10^6). The previous
+        // implementation (Guid.GetHashCode + mod) collapsed 128 bits into ~32 of entropy
+        // and tripped Math.Abs(int.MinValue) UB on the unlucky hash.
+        var hi = RandomNumberGenerator.GetInt32(0, 1_000_000);
+        var lo = RandomNumberGenerator.GetInt32(0, 1_000_000);
+        var battleId = $"{hi:D6}{lo:D6}";
         _store.RegisterPending(new PendingBattle(battleId, viewerId));
         return new PendingMatch(battleId, _options.NodeServerUrl);
     }
diff --git a/SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs b/SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs
index 71e287e..c88d7cf 100644
--- a/SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs
+++ b/SVSim.BattleNode/Lifecycle/ScriptedLifecycle.cs
@@ -117,7 +117,7 @@ public static class ScriptedLifecycle
     private static MsgEnvelope EnvelopeForPush(NetworkBattleUri uri, IMsgBody body, string? bid = null) =>
         new(uri,
             ViewerId: FakeOpponentViewerId,
-            Uuid: "node-stub",
+            Uuid: WireConstants.ServerUuid,
             Bid: bid,
             Try: 0,
             Cat: EmitCategory.Battle,
diff --git a/SVSim.BattleNode/Protocol/WireConstants.cs b/SVSim.BattleNode/Protocol/WireConstants.cs
new file mode 100644
index 0000000..78a0504
--- /dev/null
+++ b/SVSim.BattleNode/Protocol/WireConstants.cs
@@ -0,0 +1,27 @@
+namespace SVSim.BattleNode.Protocol;
+
+/// <summary>
+/// String constants that show up on the wire as opaque tags. Lifting them out of
+/// inline string literals gives each one a single source of truth and a name that
+/// reads at the use site.
+/// </summary>
+internal static class WireConstants
+{
+    /// <summary>SIO event name for ordered server-pushed frames (the lifecycle channel).</summary>
+    public const string SynchronizeEvent = "synchronize";
+
+    /// <summary>SIO event name for client-emitted msg frames + their ack-responses.</summary>
+    public const string MsgEvent = "msg";
+
+    /// <summary>SIO event name for Gungnir keepalive frames (both directions).</summary>
+    public const string AliveEvent = "alive";
+
+    /// <summary>
+    /// Placeholder UUID we stamp on every server-originated envelope. Prod servers stamp a
+    /// real per-request UUID; the client doesn't validate it.
+    /// </summary>
+    public const string ServerUuid = "node-stub";
+
+    /// <summary>Gungnir scs/ocs value the v1 server reports unconditionally.</summary>
+    public const string OnlineStatus = "ONLINE";
+}
diff --git a/SVSim.BattleNode/Sessions/BattleSession.cs b/SVSim.BattleNode/Sessions/BattleSession.cs
index a5afdd3..43b89c9 100644
--- a/SVSim.BattleNode/Sessions/BattleSession.cs
+++ b/SVSim.BattleNode/Sessions/BattleSession.cs
@@ -112,10 +112,10 @@ public sealed class BattleSession
         {
             switch (frame.EventName)
             {
-                case "msg" when frame.BinaryAttachments.Count == 1:
+                case WireConstants.MsgEvent when frame.BinaryAttachments.Count == 1:
                     await HandleMsgEventAsync(frame);
                     return;
-                case "alive" when frame.BinaryAttachments.Count == 1:
+                case WireConstants.AliveEvent when frame.BinaryAttachments.Count == 1:
                     await HandleAliveEventAsync(frame);
                     return;
             }
@@ -178,14 +178,14 @@ public sealed class BattleSession
             var aliveEnv = new MsgEnvelope(
                 Uri: NetworkBattleUri.Gungnir,
                 ViewerId: ScriptedLifecycle.FakeOpponentViewerId,
-                Uuid: "node-stub",
+                Uuid: WireConstants.ServerUuid,
                 Bid: null,
                 Try: 0,
                 Cat: EmitCategory.General,
                 PubSeq: null,
                 PlaySeq: null,
-                Body: new AlivePushBody(Scs: "ONLINE", Ocs: "ONLINE"));
-            await PushNoStockAsync(aliveEnv, eventName: "alive");
+                Body: new AlivePushBody(Scs: WireConstants.OnlineStatus, Ocs: WireConstants.OnlineStatus));
+            await PushNoStockAsync(aliveEnv, eventName: WireConstants.AliveEvent);
         }
         catch (Exception ex)
         {
@@ -272,7 +272,7 @@ public sealed class BattleSession
     private MsgEnvelope BuildAckedEnvelope(NetworkBattleUri uri) => new(
         uri,
         ViewerId: ScriptedLifecycle.FakeOpponentViewerId,
-        Uuid: "node-stub",
+        Uuid: WireConstants.ServerUuid,
         Bid: null,
         Try: 0,
         Cat: EmitCategory.General,
@@ -283,7 +283,7 @@ public sealed class BattleSession
     private MsgEnvelope BuildBattleFinishNoContest() => new(
         NetworkBattleUri.BattleFinish,
         ViewerId: ScriptedLifecycle.FakeOpponentViewerId,
-        Uuid: "node-stub",
+        Uuid: WireConstants.ServerUuid,
         Bid: null,
         Try: 0,
         Cat: EmitCategory.Battle,
@@ -317,10 +317,10 @@ public sealed class BattleSession
         return Array.Empty<long>();
     }
 
-    private Task PushOrderedAsync(MsgEnvelope env, string eventName = "synchronize") =>
+    private Task PushOrderedAsync(MsgEnvelope env, string eventName = WireConstants.SynchronizeEvent) =>
         EncodeAndSendAsync(Outbound.AssignAndArchive(env), eventName);
 
-    private Task PushNoStockAsync(MsgEnvelope env, string eventName = "synchronize") =>
+    private Task PushNoStockAsync(MsgEnvelope env, string eventName = WireConstants.SynchronizeEvent) =>
         EncodeAndSendAsync(Outbound.WrapNoStock(env), eventName);
 
     private async Task EncodeAndSendAsync(MsgEnvelope env, string eventName)