MCP Context Provider fails with filesystem server due to missing listResources() method

[casistack]

Before submitting your bug report

• I believe this is a bug. I'll try to join the Continue Discord for questions
• I'm not able to find an open issue that reports the same bug
• I've seen the troubleshooting guide on the Continue Docs

Relevant environment info

## Technical Details
- Error occurs in `MCPConnectionSingleton.modifyConfig()` in `core/context/mcp/index.ts`
- The filesystem server implements the MCP protocol correctly but doesn't include optional listing methods
- The error code -32601 is a standard JSON-RPC error for "Method not found"

## Environment
- Continue Version: 0.9.239
- VS Code Version: 1.95.3
- OS: Linux 
- Node.js: v18.20.5
- MCP Server: @modelcontextprotocol/server-filesystem@latest

Description

The MCP Context Provider in Continue.dev fails when using the official @modelcontextprotocol/server-filesystem because it assumes the server implements listResources(), listTools(), and listPrompts() methods. However, looking at the code in core/context/mcp/index.ts, these methods are called unconditionally in modifyConfig() without checking if they exist:

async modifyConfig(config: ContinueConfig): Promise<ContinueConfig> {
  // ... connection code ...

  // This fails with "Method not found" error
  const { resources } = await this.client.listResources();

  // These methods might also not exist
  const { tools } = await this.client.listTools();
  const { prompts } = await this.client.listPrompts();
}

To reproduce

1. Install the filesystem server:

npm install -g @modelcontextprotocol/server-filesystem

2. Configure MCP in ~/.continue/config.json:

{
  "experimental": {
    "modelContextProtocolServer": {
      "transport": {
        "type": "stdio",
        "command": "npx",
        "args": [
          "-y",
          "@modelcontextprotocol/server-filesystem",
          "/path/to/directory"
        ]
      }
    }
  }
}

Log output

[Extension Host] Secure MCP Filesystem Server running on stdio
[Extension Host] Allowed directories: [ '/home/m/m/m/claude-desktop-test' ]
[Extension Host] MCP connection error: Error: MCP error -32601: Method not found
at Client.onresponse (/home/m/.vscode/extensions/continue.continue-0.9.239-linux-x64/out/extension.js:105772:25)
at StdioClientTransport.transport.onmessage (/home/m/.vscode/extensions/continue.continue-0.9.239-linux-x64/out/extension.js:105675:18)
at StdioClientTransport.processReadBuffer (/home/m/.vscode/extensions/continue.continue-0.9.239-linux-x64/out/extension.js:106336:78)
at Socket.<anonymous> (/home/m/.vscode/extensions/continue.continue-0.9.239-linux-x64/out/extension.js:106311:18)
at Socket.emit (node:events:519:28)
at Socket.emit (node:domain:488:12)
at addChunk (node:internal/streams/readable:559:12)
at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)
at Socket.Readable.push (node:internal/streams/readable:390:5)
at Pipe.onStreamRead (node:internal/stream_base_commons:191:23)

[Patrick-Erichsen]

Thanks for the thorough writeup here @casistack !