diff --git a/SVSim.BattleNode/Bridge/MatchingBridge.cs b/SVSim.BattleNode/Bridge/MatchingBridge.cs
index 337441d..2436dbf 100644
--- a/SVSim.BattleNode/Bridge/MatchingBridge.cs
+++ b/SVSim.BattleNode/Bridge/MatchingBridge.cs
@@ -24,20 +24,35 @@ public sealed class MatchingBridge : IMatchingBridge
         _options = options;
     }
 
+    private const int MaxIdRetries = 5;
+
     public PendingMatch RegisterBattle(BattlePlayer p1, BattlePlayer? p2, BattleType type)
     {
         ValidateContract(p1, p2, type);
+        EvictStaleForViewer(p1.ViewerId);
+        if (p2 is not null) EvictStaleForViewer(p2.ViewerId);
 
-        // Decimal battle id mirrors the captures (e.g. "975695075012"): two unbiased
-        // BattleIdHalfDigits-wide draws concatenated. RandomNumberGenerator.GetInt32 uses
-        // rejection sampling so each half is uniform on [0, BattleIdHalfExclusiveMax).
-        var hi = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
-        var lo = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
         var halfFormat = "D" + BattleIdHalfDigits;
-        var battleId = hi.ToString(halfFormat) + lo.ToString(halfFormat);
 
-        _store.RegisterPending(new PendingBattle(battleId, type, p1, p2));
-        return new PendingMatch(battleId, _options.NodeServerUrl);
+        for (var attempt = 0; attempt < MaxIdRetries; attempt++)
+        {
+            var hi = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
+            var lo = RandomNumberGenerator.GetInt32(0, BattleIdHalfExclusiveMax);
+            var battleId = hi.ToString(halfFormat) + lo.ToString(halfFormat);
+
+            if (_store.TryRegisterPending(new PendingBattle(battleId, type, p1, p2)))
+                return new PendingMatch(battleId, _options.NodeServerUrl);
+        }
+
+        throw new InvalidOperationException(
+            $"Failed to mint a unique battle id after {MaxIdRetries} attempts.");
+    }
+
+    private void EvictStaleForViewer(long viewerId)
+    {
+        var stale = _store.TryFindPendingForViewer(viewerId);
+        if (stale is not null)
+            _store.RemovePending(stale.BattleId);
     }
 
     private static void ValidateContract(BattlePlayer p1, BattlePlayer? p2, BattleType type)
diff --git a/SVSim.BattleNode/Sessions/IBattleSessionStore.cs b/SVSim.BattleNode/Sessions/IBattleSessionStore.cs
index 1221b79..718c68c 100644
--- a/SVSim.BattleNode/Sessions/IBattleSessionStore.cs
+++ b/SVSim.BattleNode/Sessions/IBattleSessionStore.cs
@@ -2,8 +2,10 @@ namespace SVSim.BattleNode.Sessions;
 
 public interface IBattleSessionStore
 {
-    /// <summary>Register a battle minted by the matching bridge, awaiting a WS connect.</summary>
-    void RegisterPending(PendingBattle battle);
+    /// <summary>Register a battle minted by the matching bridge, awaiting a WS connect.
+    /// Returns false if a battle with the same id is already pending (caller should retry
+    /// with a fresh id).</summary>
+    bool TryRegisterPending(PendingBattle battle);
 
     /// <summary>Look up the pending battle. Returns null if not present.</summary>
     PendingBattle? TryGetPending(string battleId);
diff --git a/SVSim.BattleNode/Sessions/InMemoryBattleSessionStore.cs b/SVSim.BattleNode/Sessions/InMemoryBattleSessionStore.cs
index 360fa35..dad18d5 100644
--- a/SVSim.BattleNode/Sessions/InMemoryBattleSessionStore.cs
+++ b/SVSim.BattleNode/Sessions/InMemoryBattleSessionStore.cs
@@ -6,8 +6,8 @@ public sealed class InMemoryBattleSessionStore : IBattleSessionStore
 {
     private readonly ConcurrentDictionary<string, PendingBattle> _pending = new();
 
-    public void RegisterPending(PendingBattle battle) =>
-        _pending[battle.BattleId] = battle;
+    public bool TryRegisterPending(PendingBattle battle) =>
+        _pending.TryAdd(battle.BattleId, battle);
 
     public PendingBattle? TryGetPending(string battleId) =>
         _pending.TryGetValue(battleId, out var b) ? b : null;
diff --git a/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs b/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
index a0f030d..84ac36a 100644
--- a/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
+++ b/SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs
@@ -76,6 +76,21 @@ public class MatchingBridgeTests
                 new BattlePlayer(1, FixtureCtx()), new BattlePlayer(2, FixtureCtx()), BattleType.Bot));
     }
 
+    [Test]
+    public void RegisterBattle_evicts_stale_pending_for_same_viewer()
+    {
+        var store = new InMemoryBattleSessionStore();
+        var bridge = new MatchingBridge(store, new BattleNodeOptions());
+        var p1 = new BattlePlayer(42, FixtureCtx());
+
+        var first = bridge.RegisterBattle(p1, p2: null, BattleType.Bot);
+        Assert.That(store.TryGetPending(first.BattleId), Is.Not.Null);
+
+        var second = bridge.RegisterBattle(p1, p2: null, BattleType.Bot);
+        Assert.That(store.TryGetPending(first.BattleId), Is.Null, "stale entry must be evicted");
+        Assert.That(store.TryGetPending(second.BattleId), Is.Not.Null);
+    }
+
     private static MatchContext FixtureCtx() => new(
         SelfDeckCardIds: Enumerable.Range(1, 30).Select(i => 100_011_010L).ToList(),
         ClassId: "1", CharaId: "1", CardMasterName: "card_master_node_10015",
diff --git a/SVSim.UnitTests/BattleNode/Sessions/InMemoryBattleSessionStoreTests.cs b/SVSim.UnitTests/BattleNode/Sessions/InMemoryBattleSessionStoreTests.cs
index e24e31c..1460006 100644
--- a/SVSim.UnitTests/BattleNode/Sessions/InMemoryBattleSessionStoreTests.cs
+++ b/SVSim.UnitTests/BattleNode/Sessions/InMemoryBattleSessionStoreTests.cs
@@ -7,39 +7,40 @@ namespace SVSim.UnitTests.BattleNode.Sessions;
 [TestFixture]
 public class InMemoryBattleSessionStoreTests
 {
-    private InMemoryBattleSessionStore _store = null!;
-
-    [SetUp] public void Setup() => _store = new InMemoryBattleSessionStore();
-
     [Test]
-    public void RegisterThenGet_ReturnsRegisteredBattle()
+    public void TryRegisterThenGet_ReturnsRegisteredBattle()
     {
+        var store = new InMemoryBattleSessionStore();
         var battle = new PendingBattle("bid-1", BattleType.Bot, new BattlePlayer(906243102, FixtureCtx()), null);
-        _store.RegisterPending(battle);
+        Assert.That(store.TryRegisterPending(battle), Is.True);
 
-        Assert.That(_store.TryGetPending("bid-1"), Is.EqualTo(battle));
+        Assert.That(store.TryGetPending("bid-1"), Is.EqualTo(battle));
     }
 
     [Test]
     public void Get_UnknownBattleId_ReturnsNull()
     {
-        Assert.That(_store.TryGetPending("nope"), Is.Null);
+        var store = new InMemoryBattleSessionStore();
+        Assert.That(store.TryGetPending("nope"), Is.Null);
     }
 
     [Test]
     public void Remove_ReturnsTrueWhenPresent_FalseWhenAbsent()
     {
-        _store.RegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(1, FixtureCtx()), null));
-        Assert.That(_store.RemovePending("bid"), Is.True);
-        Assert.That(_store.RemovePending("bid"), Is.False);
+        var store = new InMemoryBattleSessionStore();
+        store.TryRegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(1, FixtureCtx()), null));
+        Assert.That(store.RemovePending("bid"), Is.True);
+        Assert.That(store.RemovePending("bid"), Is.False);
     }
 
     [Test]
-    public void Register_DuplicateBattleId_OverwritesPrior()
+    public void TryRegister_DuplicateBattleId_ReturnsFalseAndPreservesOriginal()
     {
-        _store.RegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(1, FixtureCtx()), null));
-        _store.RegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(2, FixtureCtx()), null));
-        Assert.That(_store.TryGetPending("bid")!.P1.ViewerId, Is.EqualTo(2));
+        var store = new InMemoryBattleSessionStore();
+        store.TryRegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(1, FixtureCtx()), null));
+        var second = store.TryRegisterPending(new PendingBattle("bid", BattleType.Bot, new BattlePlayer(2, FixtureCtx()), null));
+        Assert.That(second, Is.False);
+        Assert.That(store.TryGetPending("bid")!.P1.ViewerId, Is.EqualTo(1));
     }
 
     private static MatchContext FixtureCtx() => new(