NEO-146: fix in-memory create/complete lock ordering

Nest player and instance locks in TryCreateActive, TryMarkComplete, and
TryClearInstance so concurrent create and complete cannot leave a stale
active index or mismatched snapshot.

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 (`871` tests green).
+- **Tests:** `InMemoryContractInstanceStoreTests`, `InMemoryContractOutcomeStoreTests`, Postgres persistence integration tests; host DI smoke (`872` 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

@@ -227,6 +227,44 @@ public sealed class InMemoryContractInstanceStoreTests
         Assert.False(created);
     }
 
+    [Fact]
+    public async Task TryCreateActiveAndTryMarkComplete_ShouldKeepActiveIndexConsistent_WhenRacingOnSameInstanceId()
+    {
+        // Arrange
+        var store = CreateStore();
+        // Act
+        await Task.WhenAll(
+            Enumerable.Range(0, 32).Select(i => Task.Run(() =>
+            {
+                if (i % 2 == 0)
+                {
+                    _ = store.TryCreateActive(
+                        PlayerId,
+                        InstanceId,
+                        TemplateId,
+                        SeedBucket,
+                        IssuedAt,
+                        out _);
+                    return;
+                }
+
+                _ = store.TryMarkComplete(PlayerId, InstanceId, CompletedAt, 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);
+        }
+
+        if (store.TryGet(PlayerId, InstanceId, out var final) &&
+            final.Status == ContractInstanceStatus.Completed)
+        {
+            Assert.False(store.TryGetActiveForPlayer(PlayerId, out _));
+        }
+    }
+
     [Fact]
     public async Task Host_ShouldResolveContractInstanceStoresFromDi()
     {

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

@@ -152,6 +152,8 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
         }
 
         lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
+        {
+            lock (instanceLocks.GetOrAdd(ContractInstanceIds.MakeInstanceKey(player, instanceId), _ => new object()))
             {
                 if (activeInstanceByPlayer.TryGetValue(player, out var existingActiveId))
                 {
@@ -185,6 +187,7 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
                 return true;
             }
         }
+    }
 
     /// <inheritdoc />
     public bool TryMarkComplete(
@@ -207,6 +210,8 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
             return false;
         }
 
+        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
+        {
             lock (instanceLocks.GetOrAdd(lockKey, _ => new object()))
             {
                 if (!byInstanceId.TryGetValue(instanceId, out var row) ||
@@ -233,6 +238,7 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
                 return true;
             }
         }
+    }
 
     /// <inheritdoc />
     public bool TryClearInstance(string playerId, string contractInstanceId)
@@ -250,6 +256,8 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
             return false;
         }
 
+        lock (instanceLocks.GetOrAdd(PlayerLockKey(player), _ => new object()))
+        {
             lock (instanceLocks.GetOrAdd(lockKey, _ => new object()))
             {
                 if (!byInstanceId.TryGetValue(instanceId, out var row) ||
@@ -268,3 +276,4 @@ public sealed class InMemoryContractInstanceStore(IOptions<GamePositionOptions>
             }
         }
     }
+}