Lucid connector preview card fails with "MCP proxy request failed" in Codex desktop

Summary

In Codex desktop on macOS, the Lucid connector can create and export a document, and the generated Lucid web link opens correctly. The inline Codex preview card fails with:

Unable to load document
Error loading preview: MCP proxy request failed

Environment

• App: Codex desktop
• OS: macOS
• Connector: Lucid
• Test document: newly created dummy Lucidchart document

Steps To Reproduce

1. In Codex desktop, use the Lucid connector to create a diagram.
2. Wait for the generated connector result card to render in the thread.
3. Open the generated Lucid edit URL in a browser.
4. Export the same Lucid document page through the Lucid MCP tool.

Expected Behavior

Codex should render the Lucid document in the inline preview card, or show a useful recoverable preview state.

Actual Behavior

The inline preview card fails with:

Unable to load document
Error loading preview: MCP proxy request failed

The generated Lucid web URL opens correctly, and the Lucid connector can export the same document as a PNG.

Evidence

• Lucid create diagram returned canEdit: true.
• Generated Lucid web edit URL works.
• lucid_export_document_as_png for page 1 works and renders the diagram.
• The Codex app preview card is the only failing surface.
• Full document ID and thread context are available in the /feedback submission/logs.

Notes

This looks like a Codex desktop preview/proxy issue rather than a Lucid auth or connector execution issue.