big update based on real wokr

rig/ctrl/lib/config.sh

@@ -208,6 +208,29 @@ render_kind_config() {
         "$KIND_CONFIG"
 }
 
+# Render an addon's manifest (a .yaml beside its .sh) to stdout. Every ${NAME}, or
+# ${NAME:-default}, is filled from the loaded config or the calling script's variables;
+# a NAME with neither is an error, so a typo never becomes an empty image. $VAR and
+# $(VAR) are left alone: they belong to the container. Notes: docs/notes/addons.md
+render_manifest() {
+    local file="$1" text ref key def val
+    text=$(<"$file") || return 1
+    while IFS= read -r ref; do
+        key=${ref#\$\{}; key=${key%\}}; def=""
+        if [[ $key == *:-* ]]; then def=${key#*:-}; key=${key%%:-*}; fi
+        if [ -n "${!key:-}" ]; then
+            val=${!key}
+        elif [[ $ref == *:-* ]]; then
+            val=$def
+        else
+            echo "render_manifest: $file needs \${$key}, which nothing sets" >&2
+            return 1
+        fi
+        text=${text//"$ref"/"$val"}
+    done < <(grep -oE '\$\{[A-Za-z_][A-Za-z0-9_]*(:-[^}]*)?\}' "$file" | sort -u)
+    printf '%s\n' "$text"
+}
+
 _config_restore() {
     local line
     while IFS= read -r line; do