diff --git a/.jules/bolt.md b/.jules/bolt.md
index c717282b..54b216a1 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -19,3 +19,7 @@
 ## 2024-05-24 - Avoid Copying Large Sets for Membership Checks
 **Learning:** Copying a large set (e.g. 100k items) to create a snapshot for read-only membership checks is expensive O(N) and unnecessary. Python's set membership testing is thread-safe.
 **Action:** When filtering data against a shared large set, iterate and check membership directly instead of snapshotting, unless strict transactional consistency across the entire iteration is required.
+
+## 2024-05-24 - Minimize Lock Contention
+**Learning:** In parallel operations updating shared state, preparing data (parsing, filtering) inside a lock forces serialization of CPU-bound work. Moving data preparation outside the lock minimizes the critical section duration.
+**Action:** Collect/prepare data in local variables first, then update shared state in a minimal critical section (e.g. using `set.update`).
diff --git a/main.py b/main.py
index e6aabc57..600393a2 100644
--- a/main.py
+++ b/main.py
@@ -333,10 +333,13 @@ def _fetch_folder_rules(folder_id: str):
         try:
             data = _api_get(client, f"{API_BASE}/{profile_id}/rules/{folder_id}").json()
             folder_rules = data.get("body", {}).get("rules", [])
-            with all_rules_lock:
-                for rule in folder_rules:
-                    if rule.get("PK"):
-                        all_rules.add(rule["PK"])
+
+            # Optimization: Collect local rules first to minimize lock contention
+            local_rules = {rule["PK"] for rule in folder_rules if rule.get("PK")}
+
+            if local_rules:
+                with all_rules_lock:
+                    all_rules.update(local_rules)
         except httpx.HTTPError:
             pass
         except Exception as e: