- Introduced MEMORY_ENGINES_LOCK = threading.Lock() in src/cleveragents/infrastructure/database/engine_cache.py to synchronize access to the global MEMORY_ENGINES dict.
- Wrapped the MEMORY_ENGINES check-and-set in src/cleveragents/infrastructure/database/unit_of_work.py with the new lock to eliminate the TOCTOU race when multiple threads attempt to create engines for the same URL.
- Added BDD test coverage: features/tdd_engine_cache_toctou.feature with four scenarios to validate correct behavior under concurrent access.
- Added step definitions: features/steps/tdd_engine_cache_toctou_steps.py implementing the test steps.
- Updated CHANGELOG.md with the fix entry describing the TOCTOU race and lock-based fix.

ISSUES CLOSED: #7566

@@ -0,0 +28,4 @@
+
+def _get_memory_engines() -> dict[str, Any]:
+    """Return the live MEMORY_ENGINES cache dictionary."""
+    return _get_engine_cache_module().MEMORY_ENGINES  # type: ignore[no-any-return]

@@ -0,0 +57,4 @@
+def _restore_locks(ctx: Context) -> None:
+    """Restore original lock references if the tracking proxy was installed."""
+    if hasattr(ctx, "_engine_cache_module") and hasattr(ctx, "_original_lock"):
+        ctx._engine_cache_module.MEMORY_ENGINES_LOCK = ctx._original_lock  # type: ignore[assignment]

@@ -0,0 +123,4 @@
+
+    ctx._uow_module = _uow_module
+    ctx._original_uow_lock = _uow_module.MEMORY_ENGINES_LOCK
+    _uow_module.MEMORY_ENGINES_LOCK = counting_lock  # type: ignore[assignment]

@@ -0,0 +28,4 @@
+
+def _get_memory_engines() -> dict[str, Any]:
+    """Return the live MEMORY_ENGINES cache dictionary."""
+    return _get_engine_cache_module().MEMORY_ENGINES  # type: ignore[no-any-return]

@@ -0,0 +57,4 @@
+def _restore_locks(ctx: Context) -> None:
+    """Restore original lock references if the tracking proxy was installed."""
+    if hasattr(ctx, "_engine_cache_module") and hasattr(ctx, "_original_lock"):
+        ctx._engine_cache_module.MEMORY_ENGINES_LOCK = ctx._original_lock  # type: ignore[assignment]

@@ -0,0 +61,4 @@
+        if hasattr(ctx._engine_cache_module, "_original_lock_backup"):
+            del ctx._engine_cache_module._original_lock_backup
+    if hasattr(ctx, "_uow_module") and hasattr(ctx, "_original_uow_lock"):
+        ctx._uow_module.MEMORY_ENGINES_LOCK = ctx._original_uow_lock  # type: ignore[assignment]

@@ -0,0 +117,4 @@
+    counting_lock = _CountingLock()
+    ctx._engine_cache_module = engine_cache_module
+    ctx._original_lock = real_lock
+    engine_cache_module.MEMORY_ENGINES_LOCK = counting_lock  # type: ignore[assignment]

@@ -0,0 +123,4 @@
+
+    ctx._uow_module = _uow_module
+    ctx._original_uow_lock = _uow_module.MEMORY_ENGINES_LOCK
+    _uow_module.MEMORY_ENGINES_LOCK = counting_lock  # type: ignore[assignment]