diff --git a/run_agent.py b/run_agent.py
index ba0a9f93d..b65a8574a 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -3446,6 +3446,7 @@ class AIAgent:
     def _chat_messages_to_responses_input(self, messages: List[Dict[str, Any]]) -> List[Dict[str, Any]]:
         """Convert internal chat-style messages to Responses input items."""
         items: List[Dict[str, Any]] = []
+        seen_item_ids: set = set()
 
         for msg in messages:
             if not isinstance(msg, dict):
@@ -3466,7 +3467,12 @@ class AIAgent:
                     if isinstance(codex_reasoning, list):
                         for ri in codex_reasoning:
                             if isinstance(ri, dict) and ri.get("encrypted_content"):
+                                item_id = ri.get("id")
+                                if item_id and item_id in seen_item_ids:
+                                    continue
                                 items.append(ri)
+                                if item_id:
+                                    seen_item_ids.add(item_id)
                                 has_codex_reasoning = True
 
                     if content_text.strip():
@@ -3546,6 +3552,7 @@ class AIAgent:
             raise ValueError("Codex Responses input must be a list of input items.")
 
         normalized: List[Dict[str, Any]] = []
+        seen_ids: set = set()
         for idx, item in enumerate(raw_items):
             if not isinstance(item, dict):
                 raise ValueError(f"Codex Responses input[{idx}] must be an object.")
@@ -3598,8 +3605,12 @@ class AIAgent:
             if item_type == "reasoning":
                 encrypted = item.get("encrypted_content")
                 if isinstance(encrypted, str) and encrypted:
-                    reasoning_item = {"type": "reasoning", "encrypted_content": encrypted}
                     item_id = item.get("id")
+                    if isinstance(item_id, str) and item_id:
+                        if item_id in seen_ids:
+                            continue
+                        seen_ids.add(item_id)
+                    reasoning_item = {"type": "reasoning", "encrypted_content": encrypted}
                     if isinstance(item_id, str) and item_id:
                         reasoning_item["id"] = item_id
                     summary = item.get("summary")