[BUG] FleetView desktop session returns 403 for cloud MCP connectors (Slack)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Description:

Terminal claude interactive session: claude.ai Slack connected and working ✓
FleetView desktop session: same claude.ai Slack connector returns 403 on every tool call
claude mcp list from terminal shows claude.ai Slack: ✓ Connected
Hypothesis: FleetView does not properly forward OAuth credentials when proxying requests to cloud MCP servers (https://mcp.slack.com/mcp)
Environment:

macOS Darwin 25.3.0
Claude Code 2.1.142 (desktop)
MCP server: claude.ai Slack (https://mcp.slack.com/mcp)

What Should Happen?

Cloud MCP connectors (e.g. claude.ai Slack) should work in the FleetView desktop session the same way they work in the terminal Claude Code interactive session — tool calls should succeed without 403 errors.

Error Messages/Logs

Steps to Reproduce

1. Connect claude.ai Slack MCP connector via /mcp in Claude Code
2. Verify it works in terminal interactive session (claude mcp list shows ✓ Connected)
3. Open the same account in Claude Code FleetView (desktop session)
4. Ask Claude to use any Slack tool (e.g. search channels or read messages)
5. All Slack MCP tool calls return 403 error

Note: The terminal interactive session works correctly with the same connector.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.145 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_