agent_lab/backend/spa_handler.py

from fastapi.responses import JSONResponse, FileResponse
import os

async def custom_404_handler(request, exc):
    # Check if the request is for an API endpoint
    if request.url.path.startswith("/api/") or request.url.path.startswith("/ws/"):
        return JSONResponse({"detail": "Not Found"}, status_code=404)
    
    # Otherwise/for frontend routes, return index.html for React Router to handle
    frontend_dist = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "frontend", "dist")
    html_path = os.path.join(frontend_dist, "index.html")
    if os.path.exists(html_path):
        return FileResponse(html_path)
    return JSONResponse({"detail": "Frontend not built"}, status_code=404)