NEO-116: Make Postgres TryActivate safe under concurrent insert.

Use INSERT ON CONFLICT DO NOTHING so duplicate activations return false
with the existing snapshot instead of raising a primary-key violation.

server/NeonSprawl.Server.Tests/Game/Quests/PlayerQuestProgressPersistenceIntegrationTests.cs

@@ -16,6 +16,34 @@ public sealed class PlayerQuestProgressPersistenceIntegrationTests(PostgresInteg
     private const string PlayerId = "dev-local-1";
     private static readonly DateTimeOffset CompletedAt = new(2026, 6, 3, 14, 30, 0, TimeSpan.Zero);
 
+    [RequirePostgresFact]
+    public async Task TryActivate_ShouldReturnOneTrueAndRestFalse_WhenCalledConcurrently()
+    {
+        // Arrange
+        await ResetQuestProgressTableAsync();
+        const int concurrentCalls = 8;
+        var questId = PrototypeE7M1QuestCatalogRules.GatherIntroQuestId;
+
+        // Act
+        var results = await Task.WhenAll(
+            Enumerable.Range(0, concurrentCalls).Select(_ => Task.Run(() =>
+            {
+                using var scope = Factory.Services.CreateScope();
+                var store = scope.ServiceProvider.GetRequiredService<IPlayerQuestStateStore>();
+                return store.TryActivate(PlayerId, questId, out QuestStepState _);
+            })));
+
+        // Assert
+        Assert.Equal(1, results.Count(static r => r));
+        Assert.Equal(concurrentCalls - 1, results.Count(static r => !r));
+        Assert.True(
+            Factory.Services.CreateScope().ServiceProvider
+                .GetRequiredService<IPlayerQuestStateStore>()
+                .TryGetProgress(PlayerId, questId, out var snapshot));
+        Assert.Equal(QuestProgressStatus.Active, snapshot.Status);
+        Assert.Equal(0, snapshot.CurrentStepIndex);
+    }
+
     [RequirePostgresFact]
     public async Task ActivateCounterComplete_ShouldPersistAcrossNewFactory()
     {

server/NeonSprawl.Server/Game/Quests/PostgresPlayerQuestStateStore.cs

@@ -68,6 +68,29 @@ public sealed class PostgresPlayerQuestStateStore(Npgsql.NpgsqlDataSource dataSo
             return false;
         }
 
+        using var insert = new Npgsql.NpgsqlCommand(
+            """
+            INSERT INTO player_quest_progress (player_id, quest_id, status, current_step_index, objective_counters, updated_at)
+            VALUES (@pid, @qid, 'active', 0, '{}'::jsonb, now())
+            ON CONFLICT (player_id, quest_id) DO NOTHING;
+            """,
+            conn,
+            tx);
+        insert.Parameters.AddWithValue("pid", player);
+        insert.Parameters.AddWithValue("qid", quest);
+        if (insert.ExecuteNonQuery() > 0)
+        {
+            tx.Commit();
+            snapshot = new QuestStepState(
+                player,
+                quest,
+                QuestProgressStatus.Active,
+                0,
+                new Dictionary<string, int>(StringComparer.Ordinal),
+                null);
+            return true;
+        }
+
         using (var sel = new Npgsql.NpgsqlCommand(
                    """
                    SELECT status, current_step_index, objective_counters, completed_at
@@ -82,33 +105,17 @@ public sealed class PostgresPlayerQuestStateStore(Npgsql.NpgsqlDataSource dataSo
             sel.Parameters.AddWithValue("pid", player);
             sel.Parameters.AddWithValue("qid", quest);
             using var reader = sel.ExecuteReader();
-            if (reader.Read())
+            if (!reader.Read())
             {
-                snapshot = ReadSnapshot(reader, player, quest);
                 tx.Rollback();
                 return false;
             }
+
+            snapshot = ReadSnapshot(reader, player, quest);
         }
 
-        using var insert = new Npgsql.NpgsqlCommand(
+        tx.Rollback();
-            """
+        return false;
-            INSERT INTO player_quest_progress (player_id, quest_id, status, current_step_index, objective_counters, updated_at)
-            VALUES (@pid, @qid, 'active', 0, '{}'::jsonb, now());
-            """,
-            conn,
-            tx);
-        insert.Parameters.AddWithValue("pid", player);
-        insert.Parameters.AddWithValue("qid", quest);
-        insert.ExecuteNonQuery();
-        tx.Commit();
-        snapshot = new QuestStepState(
-            player,
-            quest,
-            QuestProgressStatus.Active,
-            0,
-            new Dictionary<string, int>(StringComparer.Ordinal),
-            null);
-        return true;
     }
 
     /// <inheritdoc />