completely hides homemanager build failure reasons

[CodeF53]

I have confirmed that this is a bug related to nh

• This is a bug, and not an user error or a support request. I understand that my issue will be closed if it is not a bug in NH.
• I have checked the issues tab and confirmed that my issue has not yet been reported. I understand that my issue will be closed if it is a duplicate.

Description

whenever homemanager has the stupid Existing file '...' would be clobbered thing, nh os switch ~/nixConfig --hostname ${extras.host} will just output

...: home-manager-cassie.service: Main process exited, code=exited, status=1/FAILURE
...: home-manager-cassie.service: Failed with result 'exit-code'.
...: Failed to start Home Manager environment for cassie.

without saying the actual error

Installation Method

Stable Release (nixpkgs, pkgs.nh from nixos-unstable or nixos-yy-mm)

Installation Method (Other)

No response

NH Version

nh 4.2.0

System Information

• system: "x86_64-linux"
• host os: Linux 6.12.60, NixOS, 26.05 (Yarara), 26.05.20251202.418468a
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.31.2
• nixpkgs: /nix/store/xsdf4r7hl94n1a1kjj02ibs611jnmadn-source

[NotAShelf]

This is intentional. Though, it has been made opt-in through --show-activation-hints in the master branch, and will be available in Nixpkgs as of 4.3.0.