fix(mcp): handle MCP server connection failures (#769)

[xiaoju111a]

Summary

• Change MCP connection failures from fatal errors to warnings
• Allow CLI to start even when some MCP servers fail to connect
• Successfully connected MCP servers remain available
• Improves fault tolerance and user experience

Fixes #769 #1102

Related Issue

Problem

Currently, when Kimi Code CLI starts, if any configured MCP (Model Context Protocol) server fails to connect, the CLI immediately exits with a fatal error. This "all-or-nothing" approach prevents users from accessing the interactive interface even when they only need built-in tools or other working MCP servers.

Root Cause

The original design used a "fail fast" principle for synchronous MCP loading. Later, the code was refactored to support background loading (in_background=True by default) for faster startup. However, the error handling wasn't updated accordingly - the background task still raised MCPRuntimeError on connection failures, which caused delayed crashes when wait_for_mcp_tools() was called.

Solution

This PR changes the behavior to be more fault-tolerant:

1. Changed exception to warning: In toolset.py:302, replaced raise MCPRuntimeError(...) with logger.warning(...)
2. Updated documentation: Removed MCPRuntimeError from docstrings in agent.py and app.py to reflect the new behavior
3. Graceful degradation: Failed MCP servers are logged with warnings, while successfully connected servers remain fully functional

Changes Made

Modified Files:

• src/kimi_cli/soul/toolset.py - Changed error raising to warning logging
• src/kimi_cli/soul/agent.py - Updated docstring
• src/kimi_cli/app.py - Updated docstring

Impact Analysis

• No breaking changes: Only affects failure scenarios
• Backward compatible: Successful connections work exactly as before
• No test dependencies: No existing tests rely on MCPRuntimeError being raised
• Improved UX: Users can continue working even when some MCP servers are unavailable

Testing

Manual Testing Steps

1. Configure a broken MCP server in ~/.kimi/mcp.json:

{
  "mcpServers": {
    "broken-server": {
      "command": "nonexistent-command",
      "args": []
    }
  }
}

2. Run kimi "hello world"

Expected behavior:

• CLI starts successfully
• Warning message appears about failed MCP server
• CLI remains functional with built-in tools

Before this fix:

• CLI would crash with MCPRuntimeError
• No access to any functionality

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue (MCP 连接失败时不应自动退出 - 建议与 Codex/Claude Code 保持一致 || MCP should not exit automatically when connection fails - it is recommended to be consistent with Codex/Claude Code #769).
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

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[devin-ai-integration]

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