unable to clone the nimbus repo

I cannot clone @cloud/nimbus into an empty repo. Sometimes I fail with this error:

@unison/http/main> clone @cloud/nimbus
Encountered exception:
HttpExceptionRequest Request {
  host                 = "api.unison-lang.org"
  port                 = 443
  secure               = True
  requestHeaders       = [("User-Agent","UCM/33666cc' (built on 2025-08-28)"),("Authorization","<REDACTED>"),("Accept","application/octet-stream"),("Content-Type","application/cbor")]
  path                 = "/ucm/v2/sync/entities/download"
  queryString          = ""
  method               = "POST"
  proxy                = Nothing
  rawBody              = False
  redirectCount        = 10
  responseTimeout      = ResponseTimeoutNone
  requestVersion       = HTTP/1.1
  proxySecureMode      = ProxySecureWithConnect
}
 IncompleteHeaders

This paste shows me obviously in an non-empty repo. This is because I wondered if first cloning http might make cloning nimbus work, since perhaps there would be less to download. Cloning http succeeded after about 15 minutes, and this shows the failure I got after that.

Sometimes, it seems like the Downloads just stop running. I tried running this again, and its been running for about 45 minutes now, and its been stuck at Downloaded: 31504 without that number changing for more than 10 minutes

Start by reproducing the @unison/http/main> clone @cloud/nimbus request against /ucm/v2/sync/entities/download, watching the Downloaded: 31504 progress and the reported IncompleteHeaders failure. The issue mentions no source file or test; done means identifying and fixing the cause of stalled or incomplete downloads, with a regression check for this clone path.