Document foreach id collection types

Co-authored-by: piotr.gwizdala <piotr.gwizdala@grafana.com>

Author: cursoragent

internal/runtime/internal/controller/node_config_foreach.go

@@ -444,20 +444,23 @@ func objectFingerprint(id any, hashId bool) string {
 func collectionItemID(item any, key string, logger log.Logger) (any, bool) {
 	switch value := item.(type) {
 	case map[string]any:
+		// Inline object literals in Alloy decode into map[string]any.
 		val, ok := value[key]
 		if !ok {
 			logMissingCollectionID(logger, key)
 			return nil, false
 		}
 		return val, true
 	case map[string]string:
+		// Object values sourced from Go (e.g., vars) often use map[string]string.
 		val, ok := value[key]
 		if !ok {
 			logMissingCollectionID(logger, key)
 			return nil, false
 		}
 		return val, true
 	case map[string]syntax.Value:
+		// Capsules converted to objects use map[string]syntax.Value (VM canonical form).
 		val, ok := value[key]
 		if !ok {
 			logMissingCollectionID(logger, key)