map $sent_http_content_type $csp_header {
  default "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' data: https://fonts.gstatic.com; img-src 'self' data: blob: https://*.tile.openstreetmap.org https://unpkg.com; connect-src 'self' https://demo.flow-master.ai https://canvas.flow-master.ai wss://canvas.flow-master.ai; frame-ancestors 'none'; base-uri 'self'; form-action 'self'; object-src 'none'";
}

server {
  listen 80;
  server_name _;
  root /usr/share/nginx/html;
  index index.html;

  # Hardening — every response carries these.
  add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
  add_header X-Content-Type-Options "nosniff" always;
  add_header X-Frame-Options "DENY" always;
  add_header Referrer-Policy "strict-origin-when-cross-origin" always;
  add_header Permissions-Policy "camera=(), microphone=(self), geolocation=(self), payment=()" always;
  add_header Content-Security-Policy $csp_header always;
  add_header Cross-Origin-Opener-Policy "same-origin" always;
  add_header Cross-Origin-Resource-Policy "same-origin" always;
  add_header X-Robots-Tag "noindex, nofollow" always;

  # Use the cluster CoreDNS resolver for in-cluster Services AND public
  # resolvers as fallback for external hostnames (demo.flow-master.ai etc.).
  # k3s CoreDNS by default forwards external lookups, but if the forward
  # is missing the proxy_pass to demo.flow-master.ai fails with 502/504.
  # Listing public resolvers alongside ensures lookups succeed in both
  # cases. Targets use $variable form to force lazy per-request resolution.
  resolver 10.43.0.10 1.1.1.1 8.8.8.8 valid=30s ipv6=off;

  # Reverse-proxy /api to the demo backend so live mode is same-origin.
  # NOTE: proxy_pass uses a literal hostname (not a $variable) so nginx
  # resolves demo.flow-master.ai ONCE at config-load, caches it for the
  # lifetime of the worker, and never retries DNS mid-request. This is
  # the only way to eliminate the per-request DNS race that returned
  # fast 502s on cold cache. Cloudflare hides the demo origin behind
  # anycast IPs, so a single-resolution lookup is safe and stable.
  location /api/ {
    proxy_pass https://demo.flow-master.ai;
    proxy_set_header Host demo.flow-master.ai;
    proxy_set_header X-Forwarded-Proto https;
    proxy_set_header X-Forwarded-Host $host;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_ssl_server_name on;
    proxy_ssl_name demo.flow-master.ai;
    proxy_http_version 1.1;
    proxy_connect_timeout 8s;
    proxy_send_timeout 30s;
    proxy_read_timeout 30s;
    proxy_buffering off;
    proxy_next_upstream error timeout http_502 http_503 http_504;
    proxy_next_upstream_tries 3;
    proxy_next_upstream_timeout 10s;
  }

  # In-cluster LLM proxy. Returns 503 when no provider key is configured,
  # so the frontend's deterministic fallback fires gracefully.
  location /internal/canvas-llm/ {
    set $upstream_llm "http://canvas-llm-proxy.demo.svc.cluster.local:8080";
    proxy_pass $upstream_llm;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Proto https;
    proxy_http_version 1.1;
    proxy_read_timeout 60s;
    proxy_buffering off;
  }

  # SPA fallback to index.html for client-side routing.
  location / {
    try_files $uri $uri/ /index.html;
    add_header Cache-Control "no-cache" always;
    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
    add_header X-Content-Type-Options "nosniff" always;
    add_header X-Frame-Options "DENY" always;
    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
    add_header Permissions-Policy "camera=(), microphone=(self), geolocation=(self), payment=()" always;
    add_header Content-Security-Policy $csp_header always;
  }

  # Hashed static assets cache forever.
  location /assets/ {
    try_files $uri =404;
    add_header Cache-Control "public, max-age=31536000, immutable" always;
  }

  # Hide nginx version on errors.
  server_tokens off;
}