**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/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
+}