fix(core): keep valid JSON arrays out of tool-call expansion

A valid JSON array of objects took the json.loads success path and was
expanded into multiple calls, bypassing MAX_RECOVERED_ARGUMENT_OBJECTS
and the historical object-only contract for non-object roots. Parse
valid JSON directly with object-only semantics, and hold any sequence
produced by malformed-input recovery to the same per-call bound.

litellm/litellm_core_utils/prompt_templates/factory.py

@@ -5366,9 +5366,20 @@ def _parse_tool_call_arguments(
         return {}
     normalized_raw: Final = "{}" if raw == REDACTED_BY_LITELLM else raw
     from litellm.litellm_core_utils.prompt_templates.common_utils import (
+        MAX_RECOVERED_ARGUMENT_OBJECTS,
         parse_tool_call_arguments,
     )
 
+    try:
+        direct: Final = json.loads(normalized_raw)
+    except json.JSONDecodeError:
+        pass  # malformed JSON: fall through to repair / concatenated recovery
+    else:
+        # Valid JSON keeps the historical object-only contract: a non-object
+        # root (e.g. a JSON array of objects) degrades to {} rather than
+        # becoming an uncapped expansion vector.
+        return direct if isinstance(direct, dict) else {}
+
     try:
         parsed: Final = parse_tool_call_arguments(
             normalized_raw,
@@ -5381,7 +5392,15 @@ def _parse_tool_call_arguments(
         return {}
     if isinstance(parsed, dict):
         return parsed
-    if isinstance(parsed, list) and parsed and all(isinstance(item, dict) for item in parsed):
+    # Only malformed-input recovery (repair or concatenated split) can yield a
+    # sequence here; hold it to the same per-call bound as concatenated
+    # recovery so expansion is never an amplification vector.
+    if (
+        isinstance(parsed, list)
+        and parsed
+        and all(isinstance(item, dict) for item in parsed)
+        and len(parsed) <= MAX_RECOVERED_ARGUMENT_OBJECTS
+    ):
         return parsed
     return {}
 

tests/test_litellm/litellm_core_utils/prompt_templates/test_litellm_core_utils_prompt_templates_factory.py

@@ -3524,6 +3524,70 @@ def test_get_tool_calls_from_response_caps_concatenated_expansion():
     assert tool_calls == [{"id": "call_1", "name": "search", "arguments": {}}]
 
 
+def test_get_tool_calls_from_response_valid_json_array_not_expanded():
+    """
+    A valid JSON array of objects is not concatenated recovery: it keeps the
+    historical object-only semantics (degrades to {}) and never expands, so
+    it cannot bypass the per-call expansion cap.
+    """
+    from litellm.litellm_core_utils.prompt_templates.factory import (
+        get_tool_calls_from_response,
+    )
+
+    response: Final = {
+        "choices": [
+            {
+                "message": {
+                    "tool_calls": [
+                        {
+                            "id": "call_1",
+                            "function": {
+                                "name": "search",
+                                "arguments": json.dumps(
+                                    [{"query": f"q{index}"} for index in range(9)]
+                                ),
+                            },
+                        }
+                    ]
+                }
+            }
+        ]
+    }
+
+    tool_calls: Final = get_tool_calls_from_response(response)
+
+    assert tool_calls == [{"id": "call_1", "name": "search", "arguments": {}}]
+
+
+def test_get_tool_calls_from_response_valid_json_array_of_two_not_expanded():
+    """Even a small valid JSON array degrades to {} (object-only contract)."""
+    from litellm.litellm_core_utils.prompt_templates.factory import (
+        get_tool_calls_from_response,
+    )
+
+    response: Final = {
+        "choices": [
+            {
+                "message": {
+                    "tool_calls": [
+                        {
+                            "id": "call_1",
+                            "function": {
+                                "name": "search",
+                                "arguments": json.dumps([{"query": "a"}, {"query": "b"}]),
+                            },
+                        }
+                    ]
+                }
+            }
+        ]
+    }
+
+    tool_calls: Final = get_tool_calls_from_response(response)
+
+    assert tool_calls == [{"id": "call_1", "name": "search", "arguments": {}}]
+
+
 def test_get_tool_calls_from_response_non_object_arguments_returns_empty():
     from litellm.litellm_core_utils.prompt_templates.factory import (
         get_tool_calls_from_response,