Project-scoped MCP server tools show "disabled in your connector settings" in Claude Code / Cowork despite the connector being connected (same symptom as #42453)

## Summary
A project-scoped MCP server (declared in `.mcp.json`, `transport: stdio`, running via `npx mcp-remote` bridging to a remote SSE-based MCP server) shows as **connected** with all its tools loaded, but **every single tool call fails** with:

> "This tool has been disabled in your connector settings."

This happens in Claude Code / Cowork. I have not been able to find any UI setting that actually controls this — the server in question does not appear at all in Settings → Connectors (that page only lists personal/account-level connectors, not project-scoped ones from `.mcp.json`).

This looks like the same bug reported in #42453 ("Custom local MCP server tools disabled in Cowork and Claude Code, but work in Claude Chat Desktop app"), which was closed as "not planned." I'm filing this as a fresh, detailed repro in case it helps get it reopened / prioritized — it's blocking real work for me.

## Environment
- Platform: Windows 11
- Product: Claude Code (Cowork / Code tab in the desktop app)
- MCP server: project-scoped, declared in `.mcp.json`:
```json
{
"mcpServers": {
"smartlead": {
"command": "npx",
"args": ["-y", "mcp-remote", "https://mcp.smartlead.ai/sse?user_api_key=", "--transport", "sse-only"]
}
}
}
```

## Steps to reproduce
1. Open a project containing the `.mcp.json` above.
2. Start a Claude Code / Cowork session.
3. Confirm the server shows as connected (in my case: `status: connected`, `tool_count: 170`).
4. Call any read-only tool from that server, e.g. `get_campaigns`, `get_email_accounts`, `check_webhook_status`.

## Expected behavior
The tool call executes normally, since the server is connected and the tool is listed.

## Actual behavior
Every tool call returns:
```
This tool has been disabled in your connector settings.
```
Tried 3 different read-only tools, same result every time.

## Additional evidence ruling out other causes
- Not an API key / auth issue — the connection itself succeeds and the tool list loads (170 tools).
- Not a stale-session issue — reproduced identically in a **brand-new session**, after fully closing and reopening.
- Not a naming collision with an account-level connector — the server does not appear anywhere in Settings → Connectors (checked both "Conectado" and "No conectado" tabs), so there's nothing there to toggle.
- Other project-scoped MCP servers declared the same way (`.mcp.json`, `stdio`) work fine in the same session (e.g. an n8n server, a google-docs server) — so this isn't a blanket failure of all project-scoped servers, just this one.

## Related issue
#42453 (closed as "not planned") — same exact error message, same product (Cowork/Claude Code vs. working Chat interface), similar setup (local/project MCP server). Given this is a second independent report with a clean repro, could this be reopened or re-triaged?