fix(openai): tool_call delta 重复携带 function.name，增强严格客户端兼容性

在 ToolCallStart 时记录 block_index 到 tool_name 的映射，
ToolCallDelta 时同步输出 function.name，避免严格客户端丢弃无 name 的 delta。
提取 _ss_dict 辅助方法统一 stream state 中 dict 字段的初始化逻辑。

tests/core/api_format/conversion/test_cli_conversion.py

@@ -858,6 +858,7 @@ def test_tool_call_stream_index_stable_across_deltas() -> None:
     # 收集所有 tool_calls chunk
     tc_indices: list[int] = []
     tc_ids: list[str] = []
+    tc_names: list[str] = []
     for event in all_events:
         for choice in event.get("choices", []):
             tcs = choice.get("delta", {}).get("tool_calls")
@@ -865,6 +866,7 @@ def test_tool_call_stream_index_stable_across_deltas() -> None:
                 for tc in tcs:
                     tc_indices.append(tc["index"])
                     tc_ids.append(str(tc.get("id") or ""))
+                    tc_names.append(str((tc.get("function") or {}).get("name") or ""))
 
     assert len(tc_indices) >= 2, f"expected at least 2 tool_call chunks, got {len(tc_indices)}"
     # 同一个 tool call 的所有 chunk 必须使用相同的 index
@@ -875,3 +877,7 @@ def test_tool_call_stream_index_stable_across_deltas() -> None:
         "tool_call id should be repeated on every delta for strict OpenAI-compatible clients, "
         f"got: {tc_ids}"
     )
+    assert all(tc_name == "get_weather" for tc_name in tc_names), (
+        "tool_call function.name should be repeated on every delta for strict "
+        f"OpenAI-compatible clients, got: {tc_names}"
+    )

tests/core/api_format/conversion/test_openai_normalizer.py

@@ -332,6 +332,7 @@ def test_openai_stream_chunk_and_event_roundtrip_basic() -> None:
     )
     assert tool_delta["choices"][0]["delta"]["tool_calls"][0]["id"] == "call_1"
     assert tool_delta["choices"][0]["delta"]["tool_calls"][0]["index"] == 0
+    assert tool_delta["choices"][0]["delta"]["tool_calls"][0]["function"]["name"] == "get_weather"
 
     # 最终 stop chunk finish_reason=tool_calls
     assert out_chunks[-1]["choices"][0]["finish_reason"] == "tool_calls"