fix: redirect stdio MCP stderr to logs

src/kimi_cli/soul/toolset.py

@@ -6,6 +6,7 @@
 import importlib
 import inspect
 import json
+import re
 import time
 from contextvars import ContextVar
 from dataclasses import dataclass
@@ -33,6 +34,7 @@
 from kimi_cli import logger
 from kimi_cli.exception import InvalidToolError, MCPRuntimeError
 from kimi_cli.hooks.engine import HookEngine
+from kimi_cli.share import get_share_dir
 from kimi_cli.tools import SkipThisTool
 from kimi_cli.wire.types import (
     AudioURLPart,
@@ -61,6 +63,8 @@
 
 _current_session_id: ContextVar[str] = ContextVar("_current_session_id", default="")
 
+_MCP_LOG_FILENAME_PATTERN = re.compile(r"[^A-Za-z0-9_.-]+")
+
 
 def set_session_id(sid: str) -> None:
     _current_session_id.set(sid)
@@ -82,6 +86,32 @@ def get_current_tool_call_or_none() -> ToolCall | None:
     return current_tool_call.get()
 
 
+def _mcp_stdio_log_path(server_name: str) -> Path:
+    safe_name = _MCP_LOG_FILENAME_PATTERN.sub("_", server_name).strip("._") or "server"
+    return get_share_dir() / "logs" / "mcp" / f"{safe_name}.log"
+
+
+def _build_mcp_client(server_name: str, server_config: Any) -> fastmcp.Client[Any]:
+    import fastmcp
+    from fastmcp.client.transports import StdioTransport
+    from fastmcp.mcp_config import MCPConfig, StdioMCPServer
+
+    if type(server_config) is StdioMCPServer:
+        log_path = _mcp_stdio_log_path(server_name)
+        log_path.parent.mkdir(parents=True, exist_ok=True)
+        transport = StdioTransport(
+            command=server_config.command,
+            args=server_config.args,
+            env=server_config.env,
+            cwd=server_config.cwd,
+            keep_alive=server_config.keep_alive,
+            log_file=log_path,
+        )
+        return fastmcp.Client(transport)
+
+    return fastmcp.Client(MCPConfig(mcpServers={server_name: server_config}))
+
+
 type ToolType = CallableTool | CallableTool2[Any]
 
 
@@ -538,8 +568,7 @@ async def load_mcp_tools(
             MCPRuntimeError(KimiCLIException, RuntimeError): When any MCP server cannot be
                 connected.
         """
-        import fastmcp
-        from fastmcp.mcp_config import MCPConfig, RemoteMCPServer
+        from fastmcp.mcp_config import RemoteMCPServer
 
         from kimi_cli.mcp_oauth import create_mcp_oauth, has_mcp_oauth_tokens
         from kimi_cli.ui.shell.prompt import toast
@@ -644,7 +673,7 @@ async def _connect():
                         continue
                     server_config = server_config.model_copy(update={"auth": auth})
 
-                client = fastmcp.Client(MCPConfig(mcpServers={server_name: server_config}))
+                client = _build_mcp_client(server_name, server_config)
                 self._mcp_servers[server_name] = MCPServerInfo(
                     status="pending", client=client, tools=[]
                 )

tests/core/test_mcp_stdio_logging.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+
+def test_stdio_mcp_stderr_goes_to_kimi_log_file(tmp_path, monkeypatch):
+    monkeypatch.setenv("KIMI_SHARE_DIR", str(tmp_path))
+
+    from fastmcp.client.transports import StdioTransport
+    from fastmcp.mcp_config import MCPConfig
+
+    from kimi_cli.soul.toolset import _build_mcp_client
+
+    mcp_config = MCPConfig.model_validate(
+        {
+            "mcpServers": {
+                "chrome/devtools": {
+                    "command": "npx",
+                    "args": ["-y", "chrome-devtools-mcp@latest"],
+                }
+            }
+        }
+    )
+    server_config = mcp_config.mcpServers["chrome/devtools"]
+
+    client = _build_mcp_client("chrome/devtools", server_config)
+
+    assert isinstance(client.transport, StdioTransport)
+    assert client.transport.log_file == tmp_path / "logs" / "mcp" / "chrome_devtools.log"
+    assert (tmp_path / "logs" / "mcp").is_dir()
+
+
+def test_transforming_stdio_mcp_config_keeps_fastmcp_transport(tmp_path, monkeypatch):
+    monkeypatch.setenv("KIMI_SHARE_DIR", str(tmp_path))
+
+    from fastmcp.client.transports.config import MCPConfigTransport
+    from fastmcp.mcp_config import MCPConfig
+
+    from kimi_cli.soul.toolset import _build_mcp_client
+
+    mcp_config = MCPConfig.model_validate(
+        {
+            "mcpServers": {
+                "filtered": {
+                    "command": "npx",
+                    "args": ["-y", "some-mcp-server"],
+                    "include_tags": ["safe"],
+                }
+            }
+        }
+    )
+    server_config = mcp_config.mcpServers["filtered"]
+
+    client = _build_mcp_client("filtered", server_config)
+
+    assert isinstance(client.transport, MCPConfigTransport)
+    assert client.transport.config.mcpServers["filtered"].include_tags == {"safe"}