`"action":"msg"` messages with `"level":0` are silently ignored

[SaltedFishesNG]

nom silently ignores log messages like:

@nix {"action":"msg","level":0,"msg":"\u001b[35;1mwarning:\u001b[0m unable to download '\u001b[35;1mhttps://cache.nixos.org/nar/0c3rg4b4sx150cacb5yck11634m38gnbg074ijaaabqwmqc0qz9p.nar.zst\u001b[0m': HTTP error \u001b[35;1m200\u001b[0m\u001b[35;1m (curl error: Timeout was reached)\u001b[0m; retrying from offset 65428 in 633 ms (attempt 2/15)"}

or

$ nix build nixpkgs#hello --option substituters https://domain --option trusted-substituters https://domain --verbose --log-format internal-json
@nix {"action":"start","id":306939837808640,"level":4,"parent":0,"text":"evaluating derivation 'flake:nixpkgs#hello'","type":0}
@nix {"action":"msg","level":0,"msg":"\u001b[35;1mwarning:\u001b[0m ignoring untrusted substituter 'https://domain', you are not a trusted user.\nRun `man nix.conf` for more information on the `substituters` configuration option."}
@nix {"action":"msg","level":0,"msg":"\u001b[35;1mwarning:\u001b[0m ignoring the client-specified setting 'trusted-substituters', because it is a restricted setting and you are not a trusted user"}
@nix {"action":"msg","level":0,"msg":"\u001b[35;1mwarning:\u001b[0m ignoring untrusted substituter 'https://domain', you are not a trusted user.\nRun `man nix.conf` for more information on the `substituters` configuration option."}
@nix {"action":"msg","level":0,"msg":"\u001b[35;1mwarning:\u001b[0m ignoring the client-specified setting 'trusted-substituters', because it is a restricted setting and you are not a trusted user"}

The former arises from network issues and can be ignored.
The latter indicates that the user is not trusted-users and the substituter being used is not trusted-substituters; this prevents the use of the cache and is an important notification.