fix: drop empty additional_tools input items too

Follow-up Codex turns re-send the additional_tools item with an EMPTY
tools list; the empty item is still a non-standard input variant strict
providers reject, so it must be dropped even with nothing to merge —
keying the rewrite off relocated tools alone made every turn after the
first fail again. (Codex >= 26.707 'Responses Lite'; Codex issue #32086.)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

litellm/utils.py

@@ -7478,19 +7478,30 @@ def relocate_input_additional_tools(
     the request valid AND lets filter_tools_by_allowed_types apply the
     deployment's allowlist to the merged list.
 
-    Returns ``(input, tools)``; both unchanged when there is nothing to move.
+    Follow-up Codex turns re-send the item with an EMPTY tools list (tools
+    were established earlier in the thread); the empty item is still a
+    non-standard variant strict providers reject, so it is dropped even when
+    it carries nothing to merge (Codex >= 26.707 "Responses Lite"
+    serialization; see Codex issue #32086).
+
+    Returns ``(input, tools)``; both unchanged when no additional_tools item
+    is present.
     """
     if not isinstance(input, list):
         return input, tools
+    found = False
     relocated: List[dict] = []
     kept_items = []
     for item in input:
         if isinstance(item, dict) and item.get("type") == "additional_tools":
+            found = True
             relocated.extend(item.get("tools") or [])
         else:
             kept_items.append(item)
-    if not relocated:
+    if not found:
         return input, tools
+    if not relocated:
+        return kept_items, tools
     merged = list(tools) if tools is not None else []
     merged.extend(relocated)
     return kept_items, merged

tests/test_litellm/test_utils.py

@@ -4976,3 +4976,14 @@ def test_relocate_input_additional_tools() -> None:
     # string input passes through
     s_input, s_tools = relocate_input_additional_tools(input="hello", tools=None)
     assert s_input == "hello" and s_tools is None
+
+    # follow-up Codex turns re-send the item with an EMPTY tools list — the
+    # non-standard item must STILL be dropped (strict providers reject it),
+    # with the tools param left untouched
+    turn2_input = [
+        {"role": "developer", "type": "additional_tools", "tools": []},
+        {"type": "message", "role": "user", "content": [{"type": "input_text", "text": "next"}]},
+    ]
+    t2_input, t2_tools = relocate_input_additional_tools(input=turn2_input, tools=None)
+    assert [i.get("type") for i in t2_input] == ["message"]
+    assert t2_tools is None