diff --git a/sim_base_sync.py b/sim_base_sync.py
new file mode 100644
index 000000000..af0e1b372
--- /dev/null
+++ b/sim_base_sync.py
@@ -0,0 +1,9 @@
+"""Scenario B feature work — should appear in the PR diff."""
+
+
+def compute_total(items):
+    """Sum item prices; intentional issue: shadows builtin 'sum'."""
+    sum = 0
+    for item in items:
+        sum += item
+    return sum