[BUG] Chat tab disappears when switching from Anthropic login to third-party API gateway

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop

What's Wrong?

When a user switches from Anthropic login to a third-party API (3P) gateway (LiteLLM proxy), the Chat tab disappears from Claude Desktop. The Cowork and Code tabs remain; only Chat is missing.

Confirmed on a fresh device that had never received any custom managed configuration, so this is not a packaging or policy artifact.

Steps to Reproduce

1. Log into Claude Desktop with an Anthropic account — Chat tab is visible
2. Go to Settings → switch to third-party API (3P) gateway (LiteLLM endpoint)
3. Chat tab is gone. Cowork and Code tabs remain.

What Should Happen?

Either the Chat tab remains available in Claude Desktop 3P mode, or Anthropic documents that this is expected behavior so enterprise admins can set user expectations correctly.

We are also interested in whether there is a managed policy key that controls Chat tab visibility in 3P mode, similar to isClaudeCodeForDesktopEnabled for the Code tab.

Platform

Windows / macOS (reproduced on both)

Additional Information

Deployment context: university enterprise deployment routing Claude Desktop through a LiteLLM gateway. Users noticed the missing tab during an onboarding session.