NEO-146: fix stale active index race in TryGetActiveForPlayer

Read the active index under the player lock and remove stale entries
only when the indexed instance id still matches, preventing concurrent
get/complete/reissue from dropping a newer active pointer.

docs/plans/NEO-146-implementation-plan.md

@@ -68,7 +68,7 @@ Durable per-player **`ContractInstance`** rows (active/completed) and append-onl
 - **Types:** `ContractInstanceStatus`, `ContractInstanceState`, `ContractInstanceIds`, `ContractInstanceReasonCodes`, `ContractOutcomeRow`, `ContractOutcomeIds`.
 - **Stores:** `IContractInstanceStore` / `IContractOutcomeStore`; in-memory + Postgres (`V011`, `V012`) when connection string set; partial unique index + app-level one-active enforcement.
 - **DI:** `AddContractInstanceStores` in `Program.cs`; in-memory override in `InMemoryWebApplicationFactory`.
-- **Tests:** `InMemoryContractInstanceStoreTests`, `InMemoryContractOutcomeStoreTests`, Postgres persistence integration tests; host DI smoke (`874` tests green).
+- **Tests:** `InMemoryContractInstanceStoreTests`, `InMemoryContractOutcomeStoreTests`, Postgres persistence integration tests; host DI smoke (`875` tests green).
 - **In-memory outcome guard:** `InMemoryContractOutcomeStore.TryAppend` denies when **`IContractInstanceStore.TryGet`** is false (Postgres FK + player/instance SQL guard parity).
 - **Docs:** `server/README.md` contract instance + outcome store sections.
 - **Bruno:** `bruno/neon-sprawl-server/contract-stores/` health smoke (startup-only; no contract HTTP in E7M4-03).

server/NeonSprawl.Server.Tests/Game/Contracts/InMemoryContractInstanceStoreTests.cs

@@ -265,6 +265,57 @@ public sealed class InMemoryContractInstanceStoreTests
         }
     }
 
+    [Fact]
+    public async Task TryGetActiveForPlayer_ShouldKeepActiveIndexConsistent_WhenRacingWithCompleteAndReissue()
+    {
+        // Arrange
+        var store = CreateStore();
+        Assert.True(store.TryCreateActive(
+            PlayerId,
+            InstanceId,
+            TemplateId,
+            SeedBucket,
+            IssuedAt,
+            out _));
+        // Act
+        await Task.WhenAll(
+            Enumerable.Range(0, 32).Select(i => Task.Run(() =>
+            {
+                if (i % 3 == 0)
+                {
+                    _ = store.TryGetActiveForPlayer(PlayerId, out _);
+                    return;
+                }
+
+                if (i % 3 == 1)
+                {
+                    _ = store.TryMarkComplete(PlayerId, InstanceId, CompletedAt, out _);
+                    return;
+                }
+
+                _ = store.TryCreateActive(
+                    PlayerId,
+                    SecondInstanceId,
+                    TemplateId,
+                    SeedBucket,
+                    IssuedAt.AddDays(1),
+                    out _);
+            })));
+
+        // Assert
+        if (store.TryGetActiveForPlayer(PlayerId, out var active))
+        {
+            Assert.True(store.TryGet(PlayerId, active.ContractInstanceId, out var row));
+            Assert.Equal(ContractInstanceStatus.Active, row.Status);
+        }
+
+        Assert.False(
+            store.TryGet(PlayerId, InstanceId, out var first) &&
+            store.TryGet(PlayerId, SecondInstanceId, out var second) &&
+            first.Status == ContractInstanceStatus.Active &&
+            second.Status == ContractInstanceStatus.Active);
+    }
+
     [Fact]
     public void TryClearInstance_ShouldReturnTrue_WhenRowMissing()
     {

server/NeonSprawl.Server/Game/Contracts/InMemoryContractInstanceStore.cs

@@ -108,18 +108,18 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
             return false;
         }
 
-        if (!activeInstanceByPlayer.TryGetValue(player, out var instanceId))
-        {
-            return false;
-        }
-
         lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
         {
+            if (!activeInstanceByPlayer.TryGetValue(player, out var instanceId))
+            {
+                return false;
+            }
+
             if (!byInstanceId.TryGetValue(instanceId, out var row) ||
                 row.Status != ContractInstanceStatus.Active ||
                 !string.Equals(row.PlayerId, player, StringComparison.Ordinal))
             {
-                activeInstanceByPlayer.TryRemove(player, out _);
+                activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                 return false;
             }
 
@@ -164,7 +164,7 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
                         return false;
                     }
 
-                    activeInstanceByPlayer.TryRemove(player, out _);
+                    activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, existingActiveId));
                 }
 
                 if (byInstanceId.TryGetValue(instanceId, out var existing))
@@ -233,7 +233,7 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
                 }
 
                 row.MarkCompleted(completedAt);
-                activeInstanceByPlayer.TryRemove(player, out _);
+                activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                 snapshot = row.ToSnapshot();
                 return true;
             }
@@ -269,7 +269,7 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
                 _ = byInstanceId.TryRemove(instanceId, out _);
                 if (row.Status == ContractInstanceStatus.Active)
                 {
-                    activeInstanceByPlayer.TryRemove(player, out _);
+                    activeInstanceByPlayer.TryRemove(new KeyValuePair<string, string>(player, instanceId));
                 }
 
                 return true;