diff --git a/SVSim.UnitTests/AssemblyInfo.cs b/SVSim.UnitTests/AssemblyInfo.cs
new file mode 100644
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+++ b/SVSim.UnitTests/AssemblyInfo.cs
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+using NUnit.Framework;
+
+// Parallelize at the fixture level: different test classes run on separate threads, but tests
+// inside one class still execute serially. Each fixture's SVSimTestFactory owns a private
+// SQLite :memory: connection, so DB state isn't shared. Process-static caches (e.g.
+// BattlePassRepository._curveCache) hold identical data across factories because every test
+// seeds from the same JSON, so cross-fixture races on them are data-equivalent.
+// Different test classes run on separate threads, but tests inside one class stay serial. Each
+// fixture's SVSimTestFactory owns a private SQLite :memory: connection, so DB state isn't shared.
+// ParallelScope.All is unsafe today: it exposes process-static caches (BattlePassRepository
+// ._curveCache and similar) to races inside heavy-globals fixtures (LoadController,
+// PackControllerFullCatalog, StoryService), so within-fixture parallelism is gated on cleaning
+// those up first.
+[assembly: Parallelizable(ParallelScope.Fixtures)]
+