Preview panel stuck on 'Awaiting server...' when app returns 302 redirect on root path

Bug Report

Summary

The Claude Code Desktop preview panel gets stuck on "Awaiting server..." indefinitely when the dev server returns a 302 redirect on the root path /, even though the server is fully up and healthy.

Steps to Reproduce

1. Start a dev server that responds to GET / with a 302 redirect (e.g. Flask/Indico which redirects / → /bootstrap → /login)
2. Open the preview panel in Claude Code Desktop
3. Observe that the panel shows "Awaiting server..." and never loads

Expected Behavior

The preview panel should:

• Follow 3xx redirects and render the final destination, or
• Treat any 3xx response as "server is up" and load the page

Actual Behavior

The preview panel polls GET / and only proceeds on 200 OK. A 302 response is treated as "server not ready", causing it to loop forever.

Workaround

Open http://localhost:<port> directly in a browser — the server works fine there.

Environment

• Claude Code Desktop (macOS)
• Reproducible with any server that issues a redirect on the root path (Flask, Rails, Django, etc.)

Additional Context

Confirmed the server was fully healthy during reproduction:

• curl http://localhost:8000/ → HTTP 302 (fast, ~9ms)
• curl http://localhost:8000/login/ → HTTP 200
• All backing services (PostgreSQL, Redis, SMTP) responding normally

The fix could be as simple as treating 3xx status codes as "server ready" in the health-check poll, or configuring the preview to follow redirects before rendering.