fix: strip stale reasoning item IDs from local session history

src/agents/run_internal/items.py

@@ -305,6 +305,37 @@ def strip_internal_input_item_metadata(item: TResponseInputItem) -> TResponseInp
     return cast(TResponseInputItem, cleaned)
 
 
+def strip_stale_reasoning_item_ids(
+    items: list[TResponseInputItem],
+) -> list[TResponseInputItem]:
+    """Strip the ``id`` field from reasoning items in a list of input items.
+
+    Reasoning item IDs reference server-side content that only exists during the
+    original API interaction. When reasoning items are stored in a local session
+    (SQLite, file-based, etc.) and later replayed, the server no longer recognises
+    those IDs and returns a 404. Removing the ID lets the server treat the item as a
+    fresh, untracked reasoning annotation.
+
+    This is intentionally NOT applied for ``OpenAIConversationsSession``, where the
+    server itself manages item identity.
+
+    Args:
+        items: A list of input items, potentially containing reasoning items.
+
+    Returns:
+        The same list with reasoning item IDs removed where present.
+    """
+    result: list[TResponseInputItem] = []
+    for item in items:
+        if isinstance(item, dict) and item.get("type") == "reasoning" and "id" in item:
+            sanitized = dict(item)
+            sanitized.pop("id")
+            result.append(cast(TResponseInputItem, sanitized))
+        else:
+            result.append(item)
+    return result
+
+
 def _should_omit_reasoning_item_ids(reasoning_item_id_policy: ReasoningItemIdPolicy | None) -> bool:
     return reasoning_item_id_policy == "omit"
 

src/agents/run_internal/session_persistence.py

@@ -34,6 +34,7 @@
     normalize_input_items_for_api,
     run_item_to_input_item,
     strip_internal_input_item_metadata,
+    strip_stale_reasoning_item_ids,
 )
 from .oai_conversation import OpenAIServerConversationTracker
 from .run_steps import SingleStepResult
@@ -91,6 +92,11 @@ async def prepare_input_with_session(
         strip_internal_input_item_metadata(ensure_input_item_format(item)) for item in history
     ]
 
+    # When items come from a local session (not server-managed Conversations),
+    # strip reasoning item IDs to prevent stale-server-ID 404s.
+    if not is_openai_conversation_session:
+        converted_history = strip_stale_reasoning_item_ids(converted_history)
+
     new_input_list = [
         ensure_input_item_format(item) for item in ItemHelpers.input_to_new_input_list(input)
     ]

tests/test_session_reasoning_items.py

@@ -0,0 +1,46 @@
+"""Tests for stripping stale reasoning item IDs from local session history."""
+from __future__ import annotations
+
+from agents.run_internal.items import strip_stale_reasoning_item_ids
+
+
+class TestStripStaleReasoningItemIds:
+    def test_strips_id_from_reasoning_item(self) -> None:
+        items: list[dict[str, object]] = [
+            {"type": "reasoning", "id": "rs_deadbeef", "summary": []},
+        ]
+        result = strip_stale_reasoning_item_ids(items)  # type: ignore[arg-type]
+        assert result[0].get("id") is None  # type: ignore[union-attr]
+
+    def test_preserves_non_reasoning_item_ids(self) -> None:
+        items: list[dict[str, object]] = [
+            {"type": "message", "id": "msg_123", "role": "user", "content": "hi"},
+            {"type": "function_call", "id": "fc_456", "call_id": "c1", "name": "f", "arguments": "{}"},
+        ]
+        result = strip_stale_reasoning_item_ids(items)  # type: ignore[arg-type]
+        assert result[0].get("id") == "msg_123"  # type: ignore[union-attr]
+        assert result[1].get("id") == "fc_456"  # type: ignore[union-attr]
+
+    def test_reasoning_without_id_passes_through(self) -> None:
+        items: list[dict[str, object]] = [
+            {"type": "reasoning", "summary": []},
+        ]
+        result = strip_stale_reasoning_item_ids(items)  # type: ignore[arg-type]
+        assert "id" not in result[0]  # type: ignore[arg-type]
+
+    def test_mixed_items_strip_only_reasoning(self) -> None:
+        items: list[dict[str, object]] = [
+            {"type": "reasoning", "id": "rs_1", "summary": []},
+            {"type": "message", "id": "msg_1", "role": "assistant", "content": "ok"},
+            {"type": "reasoning", "id": "rs_2", "summary": []},
+            {"type": "function_call_output", "call_id": "c1", "output": "result"},
+        ]
+        result = strip_stale_reasoning_item_ids(items)  # type: ignore[arg-type]
+        assert result[0].get("id") is None  # type: ignore[union-attr]
+        assert result[1].get("id") == "msg_1"  # type: ignore[union-attr]
+        assert result[2].get("id") is None  # type: ignore[union-attr]
+        assert result[3].get("call_id") == "c1"  # type: ignore[union-attr]
+
+    def test_empty_list(self) -> None:
+        result = strip_stale_reasoning_item_ids([])
+        assert result == []