ostree: allow --no-start-daemon and --init none

The ostree planner hard-coded InitSystem::Systemd and always started
the daemon, making it impossible to install Nix during container builds
where systemd is not running.

Add InitSettings to the Ostree planner, mirroring the Linux planner.
When init is None, /nix is created directly instead of relying on the
bind mount. Remove the unused OstreeError enum.

Add a Fedora 42 container test exercising the reported scenario.

Closes: #155

Author: Mic92

.github/workflows/ci.yml

@@ -313,6 +313,7 @@ jobs:
         distro:
           - ubuntu-v22_04
           - ubuntu-v24_04
+          - fedora-v42-ostree
     steps:
       - name: Checkout repository
         uses: actions/checkout@v6

nix/tests/container-test/default.nix

@@ -24,6 +24,35 @@ let
       tester = ./default/Dockerfile;
       system = "x86_64-linux";
     };
+
+    # Fedora 42 WSL rootfs – used for the ostree planner container test
+    # (no systemd, --init none) reproducing
+    # https://github.com/NixOS/nix-installer/issues/155
+    # Re-compressed from .tar.xz to .tar.zst because podman import is
+    # extremely slow at xz decompression inside a VM.
+    "fedora-v42-ostree" =
+      let
+        xzTarball = builtins.fetchurl {
+          url = "https://dl.fedoraproject.org/pub/fedora/linux/releases/42/Container/x86_64/images/Fedora-WSL-Base-42-1.1.x86_64.tar.xz";
+          sha256 = "138vibdf0qcln3r0f116qvmq5vx8im9cy0xv2ml7r8ccsw2kvywr";
+        };
+        pkgs = forSystem "x86_64-linux" ({ pkgs, ... }: pkgs);
+      in
+      {
+        tarball =
+          pkgs.runCommand "fedora-42-rootfs.tar.zst"
+            {
+              nativeBuildInputs = with pkgs; [
+                xz
+                zstd
+              ];
+            }
+            ''
+              xz -dc ${xzTarball} | zstd -o $out
+            '';
+        tester = ./ostree/Dockerfile;
+        system = "x86_64-linux";
+      };
   };
 
   makeTest =

nix/tests/container-test/ostree/Dockerfile

@@ -0,0 +1,10 @@
+FROM default
+COPY nix-installer /nix-installer
+RUN chmod +x /nix-installer/bin/nix-installer
+# In a container build there is no systemd, so we need --init none to skip
+# daemon setup entirely — this is the scenario from
+# https://github.com/NixOS/nix-installer/issues/155
+RUN /nix-installer/bin/nix-installer install ostree --logger pretty --log-directive nix_installer=trace --init none --extra-conf "sandbox = false" --no-confirm -vvv
+ENV PATH="${PATH}:/nix/var/nix/profiles/default/bin"
+RUN nix-build --no-substitute -E 'derivation { name = "foo"; system = "x86_64-linux"; builder = "/bin/sh"; args = ["-c" "echo foobar > $out"]; }'
+RUN /nix/nix-installer uninstall --no-confirm