In GitHub's Fedora-based CI containers the directory /nix may already exist
(e.g. from the base image or a previous build layer) and is often owned by
root:root. In this situation the Nix single-user installer aborts with:
"directory /nix exists, but is not writable by you"
This caused the container build to fail during `init-nix.sh`, leaving no
working `nix` binary on PATH. As a result, the runtime wrapper
(pkmgr-wrapper.sh) reported:
"[pkgmgr-wrapper] ERROR: 'nix' binary not found on PATH."
Local runs did not show the issue because a previous installation had already
created /nix with correct ownership.
This commit makes container-mode Nix initialization fully idempotent:
• If /nix does not exist → create it with owner nix:nixbld (existing logic).
• If /nix exists but has wrong owner/group → forcibly chown -R nix:nixbld.
• A warning is emitted if /nix remains non-writable after correction.
This guarantees that the Nix installer always has writable access to /nix
and prevents the installer from aborting in CI. As a result, `pkgmgr --help`
works again inside Fedora CI containers.
https://chatgpt.com/share/69384149-9dc8-800f-8148-55817ece8e21
bf40533469