refactor: move nix experimental feature setup to nix.conf and rename pkgmgr wrapper

https://chatgpt.com/share/693dcbad-3d30-800f-acfe-22f7263f3e80

scripts/nix/lib/nix_conf_file.sh

@@ -11,45 +11,79 @@ nixconf_file_path() {
   echo "/etc/nix/nix.conf"
 }
 
-nixconf_ensure_experimental_features() {
-  local nix_conf want
-  nix_conf="$(nixconf_file_path)"
-  want="experimental-features = nix-command flakes"
+# Ensure a given nix.conf key contains required tokens (merged, no duplicates)
+nixconf_ensure_features_key() {
+  local nix_conf="$1"
+  local key="$2"
+  shift 2
+  local required=("$@")
 
   mkdir -p /etc/nix
 
+  # Create file if missing (with just the required tokens)
   if [[ ! -f "${nix_conf}" ]]; then
+    local want="${key} = ${required[*]}"
     echo "[nix-conf] Creating ${nix_conf} with: ${want}"
     printf "%s\n" "${want}" >"${nix_conf}"
     return 0
   fi
 
-  if grep -qE '^\s*experimental-features\s*=' "${nix_conf}"; then
-    if grep -qE '^\s*experimental-features\s*=.*\bnix-command\b' "${nix_conf}" \
-      && grep -qE '^\s*experimental-features\s*=.*\bflakes\b' "${nix_conf}"; then
-      echo "[nix-conf] experimental-features already correct"
+  # Key exists -> merge tokens
+  if grep -qE "^\s*${key}\s*=" "${nix_conf}"; then
+    local ok=1
+    local t
+    for t in "${required[@]}"; do
+      if ! grep -qE "^\s*${key}\s*=.*\b${t}\b" "${nix_conf}"; then
+        ok=0
+        break
+      fi
+    done
+
+    if [[ "$ok" -eq 1 ]]; then
+      echo "[nix-conf] ${key} already correct"
       return 0
     fi
 
-    echo "[nix-conf] Extending experimental-features in ${nix_conf}"
+    echo "[nix-conf] Extending ${key} in ${nix_conf}"
 
     local current
-    current="$(grep -E '^\s*experimental-features\s*=' "${nix_conf}" | head -n1 | cut -d= -f2-)"
+    current="$(grep -E "^\s*${key}\s*=" "${nix_conf}" | head -n1 | cut -d= -f2-)"
     current="$(echo "${current}" | xargs)" # trim
 
-    # Build a merged feature string without duplicates (simple token set)
-    local merged="nix-command flakes"
+    local merged=""
     local token
+
+    # Start with existing tokens
     for token in ${current}; do
       if [[ " ${merged} " != *" ${token} "* ]]; then
         merged="${merged} ${token}"
       fi
     done
 
-    sed -i "s|^\s*experimental-features\s*=.*|experimental-features = ${merged}|" "${nix_conf}"
+    # Add required tokens
+    for token in "${required[@]}"; do
+      if [[ " ${merged} " != *" ${token} "* ]]; then
+        merged="${merged} ${token}"
+      fi
+    done
+
+    merged="$(echo "${merged}" | xargs)" # trim
+
+    sed -i "s|^\s*${key}\s*=.*|${key} = ${merged}|" "${nix_conf}"
     return 0
   fi
 
+  # Key missing -> append
+  local want="${key} = ${required[*]}"
   echo "[nix-conf] Appending to ${nix_conf}: ${want}"
   printf "\n%s\n" "${want}" >>"${nix_conf}"
 }
+
+nixconf_ensure_experimental_features() {
+  local nix_conf
+  nix_conf="$(nixconf_file_path)"
+
+  # Ensure both keys to avoid prompts and cover older/alternate expectations
+  nixconf_ensure_features_key "${nix_conf}" "experimental-features" "nix-command" "flakes"
+  nixconf_ensure_features_key "${nix_conf}" "extra-experimental-features" "nix-command" "flakes"
+}