fix(anthropic): only split chunks whose tool calls carry complete arguments

Signed-off-by: Ankit Jha <ankit.jha@tradomate.one>

litellm/llms/anthropic/pass_through/adapters/streaming_iterator.py

@@ -214,13 +214,22 @@ class _CombinedChunkSplitter:
         return pieces
 
     @staticmethod
-    def _split_parallel_tool_calls(chunk: "ModelResponseStream") -> "tuple[ModelResponseStream, ...]":
-        """Return ``(chunk,)``, or one piece per tool call when a chunk opens several.
+    def _has_complete_arguments(tool_call: object) -> bool:
+        arguments: Final = _optional_attr(_optional_attr(tool_call, "function"), "arguments")
+        if not isinstance(arguments, str) or not arguments:
+            return False
+        try:
+            json.loads(arguments)
+        except ValueError:
+            return False
+        return True
 
-        Some providers send every parallel call in one chunk. The block translators
-        read only the first call's id and name and join all arguments, so the calls
-        would merge into one ``tool_use`` block. Pieces keep call order; entries that
-        share an ``index`` stay together. Argument continuations are left alone.
+    @staticmethod
+    def _split_parallel_tool_calls(chunk: "ModelResponseStream") -> "tuple[ModelResponseStream, ...]":
+        """Return ``(chunk,)``, or one piece per call when a chunk carries several whole calls.
+
+        Only chunks where every call has its full JSON arguments are split. A later
+        argument fragment could not be routed back to an earlier block.
         """
         choices: Final = _optional_attr_sequence(chunk, "choices")
         if len(choices) != 1:
@@ -229,6 +238,8 @@ class _CombinedChunkSplitter:
         tool_calls: Final = _optional_attr_sequence(delta, "tool_calls")
         if sum(1 for call in tool_calls if _optional_attr(_optional_attr(call, "function"), "name")) < 2:
             return (chunk,)
+        if not all(_CombinedChunkSplitter._has_complete_arguments(call) for call in tool_calls):
+            return (chunk,)
 
         by_index: Final[dict[object, list[object]]] = {}
         for position, call in enumerate(tool_calls):

tests/unit/llms/anthropic/pass_through/adapters/test_streaming_iterator_combined_chunk.py

@@ -360,13 +360,29 @@ def test_splitter_keeps_single_call_and_continuation_chunks_whole():
     assert _CombinedChunkSplitter._split_parallel_tool_calls(continuation) == (continuation,)
 
 
-def test_splitter_orders_pieces_by_arrival_and_groups_same_index():
+def test_splitter_orders_pieces_by_arrival():
     chunk = _tool_chunk(
         [
             _tool_call(1, "call_b", "Read", "{}"),
             _tool_call(0, "call_a", "Glob", "{}"),
-            _tool_call(0, None, None, ""),
         ]
     )
     pieces = _CombinedChunkSplitter._split_parallel_tool_calls(chunk)
-    assert [[c.index for c in p.choices[0].delta.tool_calls] for p in pieces] == [[1], [0, 0]]
+    assert [[c.index for c in p.choices[0].delta.tool_calls] for p in pieces] == [[1], [0]]
+
+
+def test_splitter_leaves_calls_that_still_need_arguments_whole():
+    """A later fragment could not be routed back to an earlier block (Greptile on #44079)."""
+    opening = _tool_chunk([_tool_call(0, "call_a", "Read", ""), _tool_call(1, "call_b", "Read", "")])
+    partial = _tool_chunk([_tool_call(0, "call_a", "Read", '{"file_path":'), _tool_call(1, "call_b", "Read", "{}")])
+    assert _CombinedChunkSplitter._split_parallel_tool_calls(opening) == (opening,)
+    assert _CombinedChunkSplitter._split_parallel_tool_calls(partial) == (partial,)
+
+
+def test_splitter_leaves_repeated_index_and_multi_choice_chunks_whole():
+    same_index = _tool_chunk([_tool_call(0, "call_a", "Read", "{}"), _tool_call(0, "call_a", "Read", "{}")])
+    assert _CombinedChunkSplitter._split_parallel_tool_calls(same_index) == (same_index,)
+
+    two_choices = _tool_chunk([_tool_call(0, "call_a", "Read", "{}"), _tool_call(1, "call_b", "Read", "{}")])
+    two_choices.choices.append(StreamingChoices(index=1, delta=Delta(content="x")))
+    assert _CombinedChunkSplitter._split_parallel_tool_calls(two_choices) == (two_choices,)