Content-Length is not sent on raw retrieval

[tucked]

$ curl --head https://my.pbnh.com/d3486ae9136e7856bc42212385ea797094475802
HTTP/1.1 200 OK
Server: nginx/1.23.4
Date: Mon, 16 Sep 2024 21:35:15 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 3549
Connection: keep-alive

$ curl --head https://my.pbnh.com/d3486ae9136e7856bc42212385ea797094475802.txt
HTTP/1.1 200 OK
Server: nginx/1.23.4
Date: Mon, 16 Sep 2024 21:35:18 GMT
Content-Type: text/plain; charset=utf-8
Connection: keep-alive

[tucked]

This does not appear to be an nginx thing:

$ docker exec nginx curl --head http://pbnh:8000/d3486ae9136e7856bc42212385ea797094475802
...
Server: gunicorn
Date: Mon, 16 Sep 2024 21:36:19 GMT
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 3549

$ docker exec nginx curl --head http://pbnh:8000/d3486ae9136e7856bc42212385ea797094475802.txt
...
Server: gunicorn
Date: Mon, 16 Sep 2024 21:36:06 GMT
Connection: close
Content-Type: text/plain; charset=utf-8