MCP 'Server is already initialized' Error Due to Double Connection Attempt

[fitchmultz]

Summary

When using MCP servers in ACP/Wire mode, kimi-cli attempts to initialize the same MCP server connection twice, causing a "Server is already initialized" error from servers that strictly follow the MCP protocol.

Environment

• kimi-cli version: 1.8.0
• Python version: 3.14.2
• OS: macOS (ARM64)
• MCP Server: RepoPrompt (but likely affects any stdio-based MCP server)

Configuration

{
  "mcpServers": {
    "RepoPrompt": {
      "command": "/Users/user/RepoPrompt/repoprompt_cli"
    }
  }
}

Steps to Reproduce

1. Configure any stdio-based MCP server in ~/.kimi/mcp.json
2. Run kimi in ACP/Wire mode with MCP tools enabled:

   kimi --print -c "Call the RepoPrompt MCP get_file_tree tool"

3. Observe the error: Error running tool: Client failed to connect: Invalid Request: Server is already initialized

Evidence

The error message:

ToolResult(
    tool_call_id='tool_xxx',
    return_value=ToolRuntimeError(
        is_error=True,
        output='',
        message='Error running tool: Client failed to connect: Invalid Request: Server is already initialized',
        ...
    )
)

Log analysis reveals double connection attempt:

2026-02-05 07:26:20.343 | INFO | kimi_cli.soul.toolset:_connect_server:259 - Connected MCP server: RepoPrompt
2026-02-05 07:26:20.344 | INFO | kimi_cli.soul.toolset:_connect_server:259 - Connected MCP server: RepoPrompt

Root Cause Analysis

In /kimi_cli/soul/toolset.py, the MCP client context is entered twice:

1. First initialization (line 249) - During server discovery in load_mcp_tools():

   async with server_info.client as client:
       for tool in await client.list_tools():
           ...

2. Second initialization (line 386) - During actual tool call in MCPTool.__call__():

   async with self._client as client:
       result = await client.call_tool(...)

The fastmcp.Client context manager sends an initialize request when entering the context. The second async with attempts another initialization on the same connection, which compliant MCP servers reject with:

{"jsonrpc":"2.0","id":1,"error":{"code":-32600,"message":"Invalid Request: Server is already initialized"}}

Verification

The kimi mcp test RepoPrompt command works correctly because it creates a fresh connection and properly closes it after the test.

Suggested Fix

Either:

1. Option A: Maintain the connection after _connect_server() instead of using async with (keep the client connected for the session lifetime)
2. Option B: Track initialization state in the client and skip the initialize request if already initialized
3. Option C: Create a new client instance for each tool call instead of reusing the same client

Additional Context

• This affects any MCP server that strictly implements the protocol's initialization requirement
• Other MCP clients (e.g., Codex) work correctly with the same server configuration
• The issue only manifests in ACP/Wire mode; kimi mcp test works fine