Remote MCP server breaks Cursor (and likely other clients) due to pre-release SDK with incompatible icons.sizes schema #1644

Describe the bug

The hosted GitHub MCP server at https://api.githubcopilot.com/mcp/ returns serverInfo.icons[].sizes as an array (["24x24"]), but MCP clients like Cursor expect it to be a string ("24x24") per older MCP spec versions. This causes a schema validation error during connection initialization, making the server completely unusable with affected clients.

Root cause:
PR #1603 (commit 6b3c375, Dec 17 2025) upgraded the MCP Go SDK from stable v1.1.0 to pre-release v1.2.0-pre.1 to enable icons. The pre-release SDK implements icons.sizes as an array per the 2025-11-25 MCP spec, but widely-used clients haven't updated their schema validation yet.

Affected version

The hosted remote server at api.githubcopilot.com/mcp/ - which appears to be running code from main branch post-PR #1603.

Local v0.25.0 (latest stable release) does NOT have this issue as it predates the icons feature.

and for Cursor I have the following:

Version: 2.2.36
VSCode Version: 1.105.1
Commit: 55c9bc11e99cedd1fb93fbb7996abf779c583150
Date: 2025-12-18T06:25:21.733Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 25.1.0

Steps to reproduce the behavior

1. Configure Cursor to use the hosted GitHub MCP server:

{
 "mcpServers": {
   "github": {
     "url": "https://api.githubcopilot.com/mcp/",
     "headers": {
       "Authorization": "Bearer <GITHUB_PAT>"
     }
   }
 }
}

2. Restart Cursor
3. Connection fails during initialization

Expected vs actual behavior

Expected: Server connects successfully and tools are available.

Actual: Connection fails with schema validation error. Server is unusable.

Logs

From Cursor MCP client logs:

{
  "code": "invalid_type",
  "expected": "string",
  "received": "array",
  "path": ["serverInfo", "icons", 0, "sizes"],
  "message": "Expected string, received array"
}

Suggested fix:
Either remove the Sizes field from icons (it's optional per spec), or revert to stable SDK v1.1.0 until wider group of standard clients support the new schema.