Checkatrade directory connector fails to connect — "Couldn't reach"

**What happened?**

Clicking Connect on the Checkatrade connector in the Connectors directory fails immediately with "Couldn't reach Checkatrade". No connection is established. Removing and re-adding produces the same result, on two separate days.

**What did you expect to happen?**

The connector to connect.

**Steps to reproduce**

1. Open the Connectors directory and click Connect on Checkatrade.
2. The error appears; no connection is established.
3. Remove and repeat — same result.

**Area:** MCP Connector (adding/managing servers)

**MCP Server:** Checkatrade (directory connector)

**Error messages or logs:**

```
Couldn't reach Checkatrade. You can check the server URL and verify
the server is running. If this persists, share this reference with
support: "ofid_1a4cf4827fd7dff5" (2026-09-02)

Same error on earlier attempt: ofid_5499180288cd1343 (2026-09-01)
```

**Additional context**

The server appears to be working — it responds normally to a direct request.

Start by reproducing the failure from the Connectors directory using the Checkatrade connector and compare it with the direct server request described in the report. Trace the MCP connector connection path and use the two reference IDs when investigating; done means Connect succeeds and establishes the connection without the "Couldn't reach" error.

索引モデルが issue の本文から書いたものです。