allow_websocket_upgrade=1 doesn't generate WebSocket proxy headers in nginx config after container restart

Checklist

• I have pulled jc21/nginx-proxy-manager:latest
• I am not using someone elses docker image
• I have searched for similar issues (both open and closed) — #5503 is related (HTTP/2) but this is a separate issue

Describe the bug

After Docker container restart/redeploy of jc21/nginx-proxy-manager:latest, NPM regenerates all proxy_host/<ID>.conf files from templates. The database has allow_websocket_upgrade=1 correctly set, but the generated nginx configuration is missing the WebSocket upgrade headers:

proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $http_connection;
proxy_http_version 1.1;

Re-saving the proxy host via the Web UI also does not fix it — the config is regenerated but the WS headers are still absent. Manually injecting the headers into the config file (then nginx -s reload) is the only reliable workaround.

To Reproduce

1. Create a proxy host with "Websocket Support" enabled (DB confirmed: allow_websocket_upgrade=1)
2. Verify the initial config has WS headers → WebSocket connections work
3. Restart the NPM container: docker restart npm
4. Check the generated config at /data/nginx/proxy_host/<ID>.conf → WS headers are gone
5. Try re-saving via NPM Web UI → config regenerated, headers still missing
6. Only manual injection of the three proxy_set_header lines into the config file restores functionality

Expected behavior

When allow_websocket_upgrade=1 is set in the DB, the template engine (/app/templates/proxy_host.conf) should consistently generate:

location / {
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $http_connection;
    proxy_http_version 1.1;

    include conf.d/include/proxy.conf;
}

This should survive container restarts and config regeneration.

Environment

• Image: jc21/nginx-proxy-manager:latest (pulled July 2026)
• OS: Debian 5.10.0-32-amd64 (kernel 5.10)
• Docker: 29.6.1
• Database: MariaDB 10.11 — DB confirmed allow_websocket_upgrade=1 for the proxy host

Additional context

• Not related to HTTP/2 (see #5503) — happens on plain HTTPS proxy hosts without HTTP/2 enabled
• The issue appears to be in the EJS template rendering pipeline where the allow_websocket_upgrade == 1 condition fails to emit WS headers during config regeneration
• Workaround: Manual injection of headers into /data/nginx/proxy_host/<ID>.conf + nginx -s reload
• Once injected manually, the headers persist until the next container restart

Locate the source corresponding to /app/templates/proxy_host.conf and the config-regeneration entry point; inspect how allow_websocket_upgrade is passed into EJS after a restart and after Web UI saves. Reproduce with a proxy host that has Websocket Support enabled, then verify the generated file consistently contains the three WebSocket headers after regeneration.