diff --git a/run_agent.py b/run_agent.py
index 48382389e..efaeba829 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -3589,7 +3589,12 @@ class AIAgent:
                                 item_id = ri.get("id")
                                 if item_id and item_id in seen_item_ids:
                                     continue
-                                items.append(ri)
+                                # Strip the "id" field — with store=False the
+                                # Responses API cannot look up items by ID and
+                                # returns 404.  The encrypted_content blob is
+                                # self-contained for reasoning chain continuity.
+                                replay_item = {k: v for k, v in ri.items() if k != "id"}
+                                items.append(replay_item)
                                 if item_id:
                                     seen_item_ids.add(item_id)
                                 has_codex_reasoning = True
@@ -3730,8 +3735,10 @@ class AIAgent:
                             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
+                    # Do NOT include the "id" in the outgoing item — with
+                    # store=False (our default) the API tries to resolve the
+                    # id server-side and returns 404.  The id is still used
+                    # above for local deduplication via seen_ids.
                     summary = item.get("summary")
                     if isinstance(summary, list):
                         reasoning_item["summary"] = summary
diff --git a/tests/run_agent/test_run_agent_codex_responses.py b/tests/run_agent/test_run_agent_codex_responses.py
index 785d85886..2b2295565 100644
--- a/tests/run_agent/test_run_agent_codex_responses.py
+++ b/tests/run_agent/test_run_agent_codex_responses.py
@@ -1249,13 +1249,17 @@ def test_chat_messages_to_responses_input_deduplicates_reasoning_ids(monkeypatch
     ]
     items = agent._chat_messages_to_responses_input(messages)
 
-    reasoning_ids = [it["id"] for it in items if it.get("type") == "reasoning"]
-    # rs_aaa should appear only once (first occurrence kept)
-    assert reasoning_ids.count("rs_aaa") == 1
-    # rs_bbb and rs_ccc should each appear once
-    assert reasoning_ids.count("rs_bbb") == 1
-    assert reasoning_ids.count("rs_ccc") == 1
-    assert len(reasoning_ids) == 3
+    reasoning_items = [it for it in items if it.get("type") == "reasoning"]
+    # Dedup: rs_aaa appears in both turns but should only be emitted once.
+    # 3 unique items total: enc_1 (from rs_aaa), enc_2 (rs_bbb), enc_3 (rs_ccc).
+    assert len(reasoning_items) == 3
+    encrypted = [it["encrypted_content"] for it in reasoning_items]
+    assert encrypted.count("enc_1") == 1
+    assert "enc_2" in encrypted
+    assert "enc_3" in encrypted
+    # IDs must be stripped — with store=False the API 404s on id lookups.
+    for it in reasoning_items:
+        assert "id" not in it
 
 
 def test_preflight_codex_input_deduplicates_reasoning_ids(monkeypatch):
@@ -1272,7 +1276,11 @@ def test_preflight_codex_input_deduplicates_reasoning_ids(monkeypatch):
     normalized = agent._preflight_codex_input_items(raw_input)
 
     reasoning_items = [it for it in normalized if it.get("type") == "reasoning"]
-    reasoning_ids = [it["id"] for it in reasoning_items]
-    assert reasoning_ids.count("rs_xyz") == 1
-    assert reasoning_ids.count("rs_zzz") == 1
+    # rs_xyz duplicate should be collapsed to one item; rs_zzz kept.
     assert len(reasoning_items) == 2
+    encrypted = [it["encrypted_content"] for it in reasoning_items]
+    assert encrypted.count("enc_a") == 1
+    assert "enc_b" in encrypted
+    # IDs must be stripped — with store=False the API 404s on id lookups.
+    for it in reasoning_items:
+        assert "id" not in it