From c69c75508607f35130eb9c7ddbbf05b82340dd3c Mon Sep 17 00:00:00 2001
From: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
Date: Thu, 21 May 2026 00:11:34 +0800
Subject: [PATCH] fix(kosong): sanitize surrogates before Kimi requests

---
 .../kosong/src/kosong/chat_provider/kimi.py   | 19 +++++++++--
 packages/kosong/tests/test_chat_provider.py   | 32 +++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/packages/kosong/src/kosong/chat_provider/kimi.py b/packages/kosong/src/kosong/chat_provider/kimi.py
index 82b6e5ac3..acae745b4 100644
--- a/packages/kosong/src/kosong/chat_provider/kimi.py
+++ b/packages/kosong/src/kosong/chat_provider/kimi.py
@@ -157,7 +157,9 @@ async def generate(
     ) -> "KimiStreamedMessage":
         messages: list[ChatCompletionMessageParam] = []
         if system_prompt:
-            messages.append({"role": "system", "content": system_prompt})
+            messages.append(
+                {"role": "system", "content": _sanitize_surrogate_strings(system_prompt)}
+            )
         messages.extend(_convert_message(message) for message in history)
 
         generation_kwargs: dict[str, Any] = {
@@ -329,7 +331,20 @@ def _convert_message(message: Message) -> ChatCompletionMessageParam:
         dumped_message.pop("content", None)
     if reasoning_content:
         dumped_message["reasoning_content"] = reasoning_content
-    return cast(ChatCompletionMessageParam, dumped_message)
+    return cast(ChatCompletionMessageParam, _sanitize_surrogate_strings(dumped_message))
+
+
+def _sanitize_surrogate_strings(value: Any) -> Any:
+    if isinstance(value, str):
+        return value.encode("utf-8", errors="surrogatepass").decode("utf-8", errors="replace")
+    if isinstance(value, list):
+        return [_sanitize_surrogate_strings(item) for item in value]
+    if isinstance(value, dict):
+        return {
+            _sanitize_surrogate_strings(key): _sanitize_surrogate_strings(item)
+            for key, item in value.items()
+        }
+    return value
 
 
 def _is_effectively_empty_content_parts(content: Sequence[ContentPart]) -> bool:
diff --git a/packages/kosong/tests/test_chat_provider.py b/packages/kosong/tests/test_chat_provider.py
index 79747ca52..b0d735d3a 100644
--- a/packages/kosong/tests/test_chat_provider.py
+++ b/packages/kosong/tests/test_chat_provider.py
@@ -1,4 +1,7 @@
 import asyncio
+import json
+from types import SimpleNamespace
+from typing import Any, cast
 
 from kosong.chat_provider import APIStatusError, StreamedMessagePart
 from kosong.chat_provider.chaos import ChaosChatProvider, ChaosConfig
@@ -41,3 +44,32 @@ async def test_chaos_chat_provider():
             raise AssertionError("Expected APIStatusError")
         except APIStatusError:
             pass
+
+
+async def test_kimi_sanitizes_surrogates_before_request():
+    class FakeCompletions:
+        def __init__(self) -> None:
+            self.kwargs: dict[str, Any] = {}
+
+        async def create(self, **kwargs: Any) -> Any:
+            request = dict(kwargs)
+            request["tools"] = list(request["tools"])
+            json.dumps(request, ensure_ascii=False).encode("utf-8")
+            self.kwargs = request
+            return SimpleNamespace()
+
+    completions = FakeCompletions()
+    chat_provider = Kimi(model="dummy", api_key="sk-1234567890")
+    chat_provider.client = cast(
+        Any, SimpleNamespace(chat=SimpleNamespace(completions=completions))
+    )
+
+    await chat_provider.generate(
+        system_prompt="system\udca9",
+        tools=[],
+        history=[Message(role="user", content=[TextPart(text="hello\udca9")])],
+    )
+
+    messages = completions.kwargs["messages"]
+    assert "\ufffd" in messages[0]["content"]
+    assert "\ufffd" in messages[1]["content"]