diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000000..22b223def6
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-05-18 - [Optimize path containment checks]
+**Learning:** Using `os.path.commonpath` for path containment checks is a significant bottleneck due to internal list allocations and path splitting.
+**Action:** Use `os.path.abspath` combined with `str.startswith()` and a conditionally appended `os.sep` to prevent path traversal bugs while being significantly faster.
diff --git a/helpers/files.py b/helpers/files.py
index c77ab54cf1..1387587949 100644
--- a/helpers/files.py
+++ b/helpers/files.py
@@ -653,7 +653,8 @@ def is_in_dir(path: str, dir: str):
     # check if the given path is within the directory
     abs_path = os.path.abspath(path)
     abs_dir = os.path.abspath(dir)
-    return os.path.commonpath([abs_path, abs_dir]) == abs_dir
+    # ⚡ Bolt Optimization: Replace slow os.path.commonpath with startswith to avoid list allocations
+    return abs_path == abs_dir or abs_path.startswith(abs_dir + ('' if abs_dir.endswith(os.sep) else os.sep))
 
 
 def get_subdirectories(