**Refactor Nix init into modular scripts and update packaging paths**

* Move the Nix bootstrap from *scripts/init-nix.sh* to *scripts/nix/init.sh* with split-out helpers in *scripts/nix/lib/*
* Update Arch/Debian/Fedora packaging hooks to call */usr/lib/package-manager/nix/init.sh*
* Keep bootstrap behavior the same while improving maintainability and reuse

https://chatgpt.com/share/693c7159-b340-800f-929e-2515eeb0dd03

scripts/nix/README.md

@@ -0,0 +1,53 @@
+# Nix Bootstrap (package-manager)
+
+This directory contains the **Nix initialization and bootstrap logic** used by *package-manager* to ensure the `nix` command is available on supported systems (host machines and CI containers).
+
+It is invoked during package installation (Arch/Debian/Fedora scriptlets) and can also be called manually.
+
+---
+
+## Entry Point
+
+- *scripts/nix/init.sh*  
+  Main bootstrap script. It:
+  - checks whether `nix` is already available
+  - adjusts `PATH` for common Nix locations
+  - installs Nix when missing (daemon install on systemd hosts, single-user in containers)
+  - ensures predictable `nix` availability via symlinks (without overwriting distro-managed paths)
+  - validates that `nix` is usable at the end (CI-safe)
+
+---
+
+## Library Layout
+
+The entry point sources small, focused modules from *scripts/nix/lib/*:
+
+- *config.sh* — configuration defaults (installer URL, retry timing)
+- *detect.sh* — container detection helpers
+- *path.sh* — PATH adjustments and `nix` binary resolution helpers
+- *symlinks.sh* — user/global symlink helpers for stable `nix` discovery
+- *users.sh* — build group/users and container ownership/perms helpers
+- *install.sh* — installer download + retry logic and execution helpers
+
+Each library file includes a simple guard to prevent double-sourcing.
+
+---
+
+## When It Runs
+
+This bootstrap is typically executed automatically:
+
+- Arch: post-install / post-upgrade hook
+- Debian: `postinst`
+- Fedora/RPM: `%post`
+
+
+---
+
+## Notes / Design Goals
+
+- **Cross-distro compatibility:** supports common Linux layouts (including Arch placing `nix` in */usr/sbin*).
+- **Non-destructive behavior:** avoids overwriting distro-managed `nix` binaries.
+- **CI robustness:** retry logic for downloads and a final `nix` availability check.
+- **Container-safe defaults:** single-user install as a dedicated `nix` user when running as root in containers.
+

scripts/nix/init.sh

@@ -0,0 +1,130 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# shellcheck source=lib/config.sh
+# shellcheck source=lib/detect.sh
+# shellcheck source=lib/path.sh
+# shellcheck source=lib/symlinks.sh
+# shellcheck source=lib/users.sh
+# shellcheck source=lib/install.sh
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+source "${SCRIPT_DIR}/lib/config.sh"
+source "${SCRIPT_DIR}/lib/detect.sh"
+source "${SCRIPT_DIR}/lib/path.sh"
+source "${SCRIPT_DIR}/lib/symlinks.sh"
+source "${SCRIPT_DIR}/lib/users.sh"
+source "${SCRIPT_DIR}/lib/install.sh"
+
+echo "[init-nix] Starting Nix initialization..."
+
+main() {
+  # Fast path: already available
+  if command -v nix >/dev/null 2>&1; then
+    echo "[init-nix] Nix already available on PATH: $(command -v nix)"
+    ensure_nix_on_path
+
+    if [[ "${EUID:-0}" -eq 0 ]]; then
+      ensure_global_nix_symlinks "$(resolve_nix_bin 2>/dev/null || true)"
+    else
+      ensure_user_nix_symlink "$(resolve_nix_bin 2>/dev/null || true)"
+    fi
+
+    return 0
+  fi
+
+  ensure_nix_on_path
+
+  if command -v nix >/dev/null 2>&1; then
+    echo "[init-nix] Nix found after PATH adjustment: $(command -v nix)"
+    if [[ "${EUID:-0}" -eq 0 ]]; then
+      ensure_global_nix_symlinks "$(resolve_nix_bin 2>/dev/null || true)"
+    else
+      ensure_user_nix_symlink "$(resolve_nix_bin 2>/dev/null || true)"
+    fi
+    return 0
+  fi
+
+  local IN_CONTAINER=0
+  if is_container; then
+    IN_CONTAINER=1
+    echo "[init-nix] Detected container environment."
+  else
+    echo "[init-nix] No container detected."
+  fi
+
+  # -------------------------------------------------------------------------
+  # Container + root: dedicated "nix" user, single-user install
+  # -------------------------------------------------------------------------
+  if [[ "$IN_CONTAINER" -eq 1 && "${EUID:-0}" -eq 0 ]]; then
+    echo "[init-nix] Container + root: installing as 'nix' user (single-user)."
+
+    ensure_nix_build_group
+
+    if ! id nix >/dev/null 2>&1; then
+      echo "[init-nix] Creating user 'nix'..."
+      local BASH_SHELL
+      BASH_SHELL="$(command -v bash || true)"
+      [[ -z "$BASH_SHELL" ]] && BASH_SHELL="/bin/sh"
+      useradd -m -r -g nixbld -s "$BASH_SHELL" nix
+    fi
+
+    ensure_nix_store_dir_for_container_user
+
+    install_nix_with_retry "no-daemon" "nix"
+
+    ensure_nix_on_path
+
+    # Ensure stable global symlink(s) (sudo secure_path friendly)
+    ensure_global_nix_symlinks "/home/nix/.nix-profile/bin/nix"
+
+    # Ensure non-root users can traverse and execute nix user profile
+    ensure_container_profile_perms
+
+  # -------------------------------------------------------------------------
+  # Host (no container)
+  # -------------------------------------------------------------------------
+  else
+    if command -v systemctl >/dev/null 2>&1; then
+      echo "[init-nix] Host with systemd: using multi-user install (--daemon)."
+      if [[ "${EUID:-0}" -eq 0 ]]; then
+        ensure_nix_build_group
+      fi
+      install_nix_with_retry "daemon"
+    else
+      echo "[init-nix] No systemd detected: using single-user install (--no-daemon)."
+      if [[ "${EUID:-0}" -eq 0 ]]; then
+        ensure_nix_build_group
+      fi
+      install_nix_with_retry "no-daemon"
+    fi
+  fi
+
+  # -------------------------------------------------------------------------
+  # After install: PATH + symlink(s)
+  # -------------------------------------------------------------------------
+  ensure_nix_on_path
+
+  local nix_bin_post
+  nix_bin_post="$(resolve_nix_bin 2>/dev/null || true)"
+
+  if [[ "${EUID:-0}" -eq 0 ]]; then
+    ensure_global_nix_symlinks "$nix_bin_post"
+  else
+    ensure_user_nix_symlink "$nix_bin_post"
+  fi
+
+  # Final verification (must succeed for CI)
+  if ! command -v nix >/dev/null 2>&1; then
+    echo "[init-nix] ERROR: nix not found after installation."
+    echo "[init-nix] DEBUG: resolved nix path = ${nix_bin_post:-<empty>}"
+    echo "[init-nix] DEBUG: PATH = $PATH"
+    exit 1
+  fi
+
+  echo "[init-nix] Nix successfully available at: $(command -v nix)"
+  echo "[init-nix] Nix initialization complete."
+}
+
+main "$@"

scripts/nix/lib/config.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+# Prevent double-sourcing
+if [[ -n "${PKGMGR_NIX_CONFIG_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_CONFIG_SH=1
+
+NIX_INSTALL_URL="${NIX_INSTALL_URL:-https://nixos.org/nix/install}"
+NIX_DOWNLOAD_MAX_TIME="${NIX_DOWNLOAD_MAX_TIME:-300}"
+NIX_DOWNLOAD_SLEEP_INTERVAL="${NIX_DOWNLOAD_SLEEP_INTERVAL:-20}"

scripts/nix/lib/detect.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+if [[ -n "${PKGMGR_NIX_DETECT_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_DETECT_SH=1
+
+# Detect whether we are inside a container (Docker/Podman/etc.)
+is_container() {
+  [[ -f /.dockerenv || -f /run/.containerenv ]] && return 0
+  grep -qiE 'docker|container|podman|lxc' /proc/1/cgroup 2>/dev/null && return 0
+  [[ -n "${container:-}" ]] && return 0
+  return 1
+}

scripts/nix/lib/install.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+
+if [[ -n "${PKGMGR_NIX_INSTALL_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_INSTALL_SH=1
+
+# Requires: NIX_INSTALL_URL, NIX_DOWNLOAD_MAX_TIME, NIX_DOWNLOAD_SLEEP_INTERVAL
+
+# Download and run Nix installer with retry
+#   Usage: install_nix_with_retry daemon|no-daemon [run_as_user]
+install_nix_with_retry() {
+  local mode="$1"
+  local run_as="${2:-}"
+  local installer elapsed=0 mode_flag
+
+  case "$mode" in
+    daemon)    mode_flag="--daemon" ;;
+    no-daemon) mode_flag="--no-daemon" ;;
+    *)
+      echo "[init-nix] ERROR: Invalid mode '$mode' (expected 'daemon' or 'no-daemon')."
+      exit 1
+      ;;
+  esac
+
+  installer="$(mktemp -t nix-installer.XXXXXX)"
+  chmod 0644 "$installer"
+
+  echo "[init-nix] Downloading Nix installer from $NIX_INSTALL_URL (max ${NIX_DOWNLOAD_MAX_TIME}s)..."
+
+  while true; do
+    if curl -fL "$NIX_INSTALL_URL" -o "$installer"; then
+      echo "[init-nix] Successfully downloaded installer to $installer"
+      break
+    fi
+
+    elapsed=$((elapsed + NIX_DOWNLOAD_SLEEP_INTERVAL))
+    echo "[init-nix] WARNING: Download failed. Retrying in ${NIX_DOWNLOAD_SLEEP_INTERVAL}s (elapsed ${elapsed}s)..."
+
+    if (( elapsed >= NIX_DOWNLOAD_MAX_TIME )); then
+      echo "[init-nix] ERROR: Giving up after ${elapsed}s trying to download Nix installer."
+      rm -f "$installer"
+      exit 1
+    fi
+
+    sleep "$NIX_DOWNLOAD_SLEEP_INTERVAL"
+  done
+
+  if [[ -n "$run_as" ]]; then
+    chown "$run_as:$run_as" "$installer" 2>/dev/null || true
+    echo "[init-nix] Running installer as user '$run_as' ($mode_flag)..."
+    if command -v sudo >/dev/null 2>&1; then
+      sudo -u "$run_as" bash -lc "sh '$installer' $mode_flag"
+    else
+      su - "$run_as" -c "sh '$installer' $mode_flag"
+    fi
+  else
+    echo "[init-nix] Running installer as current user ($mode_flag)..."
+    sh "$installer" "$mode_flag"
+  fi
+
+  rm -f "$installer"
+}

scripts/nix/lib/path.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+
+if [[ -n "${PKGMGR_NIX_PATH_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_PATH_SH=1
+
+# Ensure Nix binaries are on PATH (additive, never destructive)
+ensure_nix_on_path() {
+  if [[ -x /nix/var/nix/profiles/default/bin/nix ]]; then
+    PATH="/nix/var/nix/profiles/default/bin:$PATH"
+  fi
+  if [[ -x "$HOME/.nix-profile/bin/nix" ]]; then
+    PATH="$HOME/.nix-profile/bin:$PATH"
+  fi
+  if [[ -x /home/nix/.nix-profile/bin/nix ]]; then
+    PATH="/home/nix/.nix-profile/bin:$PATH"
+  fi
+  if [[ -d "$HOME/.local/bin" ]]; then
+    PATH="$HOME/.local/bin:$PATH"
+  fi
+  export PATH
+}
+
+# Resolve a path to a real executable (follows symlinks)
+real_exe() {
+  local p="${1:-}"
+  [[ -z "$p" ]] && return 1
+
+  local r
+  r="$(readlink -f "$p" 2>/dev/null || echo "$p")"
+
+  [[ -x "$r" ]] && { echo "$r"; return 0; }
+  return 1
+}
+
+# Resolve nix binary path robustly (works across distros + Arch /usr/sbin)
+resolve_nix_bin() {
+  local nix_cmd=""
+  nix_cmd="$(command -v nix 2>/dev/null || true)"
+  [[ -n "$nix_cmd" ]] && real_exe "$nix_cmd" && return 0
+
+  # IMPORTANT: prefer system locations before /usr/local to avoid self-symlink traps
+  [[ -x /usr/sbin/nix ]]      && { echo "/usr/sbin/nix"; return 0; } # Arch package can land here
+  [[ -x /usr/bin/nix ]]       && { echo "/usr/bin/nix"; return 0; }
+  [[ -x /bin/nix ]]           && { echo "/bin/nix"; return 0; }
+
+  # /usr/local last, and only if it resolves to a real executable
+  [[ -e /usr/local/bin/nix ]] && real_exe "/usr/local/bin/nix" && return 0
+
+  [[ -x /nix/var/nix/profiles/default/bin/nix ]] && {
+    echo "/nix/var/nix/profiles/default/bin/nix"; return 0;
+  }
+
+  [[ -x "$HOME/.nix-profile/bin/nix" ]] && {
+    echo "$HOME/.nix-profile/bin/nix"; return 0;
+  }
+
+  [[ -x "$HOME/.local/bin/nix" ]] && {
+    echo "$HOME/.local/bin/nix"; return 0;
+  }
+
+  [[ -x /home/nix/.nix-profile/bin/nix ]] && {
+    echo "/home/nix/.nix-profile/bin/nix"; return 0;
+  }
+
+  return 1
+}

scripts/nix/lib/symlinks.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+
+if [[ -n "${PKGMGR_NIX_SYMLINKS_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_SYMLINKS_SH=1
+
+# Requires: real_exe, resolve_nix_bin
+# shellcheck disable=SC2034
+
+# Ensure globally reachable nix symlink(s) (CI / non-login shells) - root only
+ensure_global_nix_symlinks() {
+  local nix_bin="${1:-}"
+
+  [[ -z "$nix_bin" ]] && nix_bin="$(resolve_nix_bin 2>/dev/null || true)"
+
+  if [[ -z "$nix_bin" || ! -x "$nix_bin" ]]; then
+    echo "[init-nix] WARNING: nix binary not found, cannot create global symlink(s)."
+    return 0
+  fi
+
+  # Always link to the real executable to avoid /usr/local/bin/nix -> /usr/local/bin/nix
+  nix_bin="$(real_exe "$nix_bin" 2>/dev/null || echo "$nix_bin")"
+
+  local targets=()
+
+  # Always provide /usr/local/bin/nix for CI shells
+  mkdir -p /usr/local/bin 2>/dev/null || true
+  targets+=("/usr/local/bin/nix")
+
+  # Provide sudo-friendly locations only if they are NOT present (do not override distro paths)
+  if [[ ! -e /usr/bin/nix ]]; then
+    targets+=("/usr/bin/nix")
+  fi
+  if [[ ! -e /usr/sbin/nix ]]; then
+    targets+=("/usr/sbin/nix")
+  fi
+
+  local target current_real
+  for target in "${targets[@]}"; do
+    current_real=""
+    if [[ -e "$target" ]]; then
+      current_real="$(real_exe "$target" 2>/dev/null || true)"
+    fi
+
+    if [[ -n "$current_real" && "$current_real" == "$nix_bin" ]]; then
+      echo "[init-nix] $target already points to: $nix_bin"
+      continue
+    fi
+
+    # If something exists but is not the same (and we promised not to override), skip.
+    if [[ -e "$target" && "$target" != "/usr/local/bin/nix" ]]; then
+      echo "[init-nix] WARNING: $target exists; not overwriting."
+      continue
+    fi
+
+    if ln -sf "$nix_bin" "$target" 2>/dev/null; then
+      echo "[init-nix] Ensured $target -> $nix_bin"
+    else
+      echo "[init-nix] WARNING: Failed to ensure $target symlink."
+    fi
+  done
+}
+
+# Ensure user-level nix symlink (works without root; CI-safe)
+ensure_user_nix_symlink() {
+  local nix_bin="${1:-}"
+
+  [[ -z "$nix_bin" ]] && nix_bin="$(resolve_nix_bin 2>/dev/null || true)"
+
+  if [[ -z "$nix_bin" || ! -x "$nix_bin" ]]; then
+    echo "[init-nix] WARNING: nix binary not found, cannot create user symlink."
+    return 0
+  fi
+
+  nix_bin="$(real_exe "$nix_bin" 2>/dev/null || echo "$nix_bin")"
+
+  mkdir -p "$HOME/.local/bin" 2>/dev/null || true
+  ln -sf "$nix_bin" "$HOME/.local/bin/nix"
+
+  echo "[init-nix] Ensured $HOME/.local/bin/nix -> $nix_bin"
+
+  PATH="$HOME/.local/bin:$PATH"
+  export PATH
+
+  if [[ -w "$HOME/.profile" ]] && ! grep -q 'nix/init.sh' "$HOME/.profile" 2>/dev/null; then
+    cat >>"$HOME/.profile" <<'EOF'
+
+# PATH for nix (added by package-manager nix/init.sh)
+if [ -d "$HOME/.local/bin" ]; then
+  PATH="$HOME/.local/bin:$PATH"
+fi
+EOF
+  fi
+}

scripts/nix/lib/users.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+if [[ -n "${PKGMGR_NIX_USERS_SH:-}" ]]; then
+  return 0
+fi
+PKGMGR_NIX_USERS_SH=1
+
+# Ensure Nix build group and users exist (build-users-group = nixbld) - root only
+ensure_nix_build_group() {
+  if ! getent group nixbld >/dev/null 2>&1; then
+    echo "[init-nix] Creating group 'nixbld'..."
+    groupadd -r nixbld
+  fi
+
+  for i in $(seq 1 10); do
+    if ! id "nixbld$i" >/dev/null 2>&1; then
+      echo "[init-nix] Creating build user nixbld$i..."
+      useradd -r -g nixbld -G nixbld -s /usr/sbin/nologin "nixbld$i"
+    fi
+  done
+}
+
+# Container-only helper: /nix ownership + perms for single-user install as 'nix'
+ensure_nix_store_dir_for_container_user() {
+  if [[ ! -d /nix ]]; then
+    echo "[init-nix] Creating /nix with owner nix:nixbld..."
+    mkdir -m 0755 /nix
+    chown nix:nixbld /nix
+    return 0
+  fi
+
+  local current_owner current_group
+  current_owner="$(stat -c '%U' /nix 2>/dev/null || echo '?')"
+  current_group="$(stat -c '%G' /nix 2>/dev/null || echo '?')"
+  if [[ "$current_owner" != "nix" || "$current_group" != "nixbld" ]]; then
+    echo "[init-nix] Fixing /nix ownership from $current_owner:$current_group to nix:nixbld..."
+    chown -R nix:nixbld /nix
+  fi
+}
+
+# Container-only helper: make nix profile executable/traversable for non-root
+ensure_container_profile_perms() {
+  if [[ -d /home/nix ]]; then
+    chmod o+rx /home/nix 2>/dev/null || true
+  fi
+  if [[ -d /home/nix/.nix-profile ]]; then
+    chmod -R o+rx /home/nix/.nix-profile 2>/dev/null || true
+  fi
+}