MCP server collision detection is case-sensitive across configuration scopes

Describe the bug

Copilot CLI can discover MCP servers from multiple scopes, including user configuration and installed plugins. Server-name collision detection is case-sensitive, so logically identical names such as MCPBrowser and mcpbrowser are treated as separate servers and both processes are launched.

This causes redundant startup work, duplicate tool registrations, additional startup delays, and confusing output where one declaration may fail or time out while the other connects successfully.

Affected version

GitHub Copilot CLI 1.0.79 on Windows x64.

Steps to reproduce the behavior

1. Add a user-scoped MCP server named MCPBrowser to ~/.copilot/mcp-config.json:

{
  "mcpServers": {
    "MCPBrowser": {
      "type": "local",
      "command": "npx",
      "args": ["-y", "mcpbrowser@latest"],
      "tools": ["*"]
    }
  }
}

2. Install a Copilot plugin that contributes the same MCP server using the name mcpbrowser.
3. Run copilot plugins list --kind mcp --json.
4. Observe both entries: user-scoped MCPBrowser and plugin-scoped mcpbrowser.
5. Start Copilot CLI and observe that both MCP processes are started independently.

Expected behavior

Copilot CLI should detect MCP name collisions case-insensitively across all discovery scopes and should not launch duplicate logical servers.

Suggested behavior:

• Canonicalize MCP names for collision detection, for example with Unicode case folding.
• Apply a documented precedence rule across user, repository, organization, and plugin scopes.
• Start only the winning declaration.
• Emit a clear warning that identifies both sources and explains which declaration was selected.
• Alternatively, fail fast with an actionable conflict error rather than silently launching both.

Exact duplicate names may already receive precedence handling; case-only differences should not bypass it.

Additional context

This is especially easy to encounter when a server was first configured manually and is later installed through a plugin. Individual MCP server packages cannot reliably prevent or repair duplicate declarations because discovery and scope resolution happen in Copilot CLI before the server process starts.

从通过 copilot plugins list --kind mcp --json 执行的 MCP 发现和作用域解析入手，将用户在 ~/.copilot/mcp-config.json 中的声明与插件声明进行比较。跟踪服务器名称在不同作用域之间进行比较的位置。完成标准是：能够检测出仅大小写不同的重复项，一项声明遵循已记录的优先级规则，并且在两个进程启动之前清楚地报告或拒绝冲突。