Cannot remove connector stuck at "Checking connection"

### What happened?

I wrote a custom training diary app and wanted to control it from claude chat, so I implemented MCP server for it.

The implementation (handled by Claude code Opus 4.8 completely) forgot to add Allow: POST header on the GET /api/mcp 405 response. This resulted in Claude hanging indefinitely when trying to connect to it. I since redeployed a fix, but the connector seems to be stuck in this waiting loop and there is no way in the Claude Desktop UI to interrupt it, retry or remove the connector and readd one with the same URL.

### What did you expect to happen?

I expected to be able to interrupt an indefinitely hanging connection process.

### Steps to reproduce

1. Connect to a static MCP server without Allow: POST header on the GET /api/mcp 405 response
2. Claude Desktop hangs indefinitely waiting for a response that never comes. Stuck in "Checking connection..."
3. It is impossible to cancel or retry the connection, once the MCP server is fixed, forcing a workaround with deploying the connector in different URL to bypass it, resulting in non-standard URL being used

### Area

MCP Connector (adding/managing servers)

### MCP Server (if applicable)

custom server

### Error messages or logs

```shell

```

### Additional context