Use explicit IDs in configuration source builders

backends.go

@@ -14,13 +14,15 @@ const BackendRakestrawHome = backend.RakestrawHomeID
 // BackendLocal is a conventional ID for a caller-configured local backend.
 const BackendLocal = "local"
 
-// BackendConfig is a presence-aware convenience value for a keyed backend
+// BackendConfig is a presence-aware convenience value for an identified backend
 // definition. Nil pointer fields are omitted, while non-nil pointers preserve
 // explicit zero or blank values. A nil ExtraParams map is omitted; a non-nil
 // empty map supplies an empty mapping. A nil SmokeTests pointer is omitted; a
 // non-nil pointer supplies a smoke_tests mapping. Use raw ConfigKit Mapping
 // inputs for explicit null. BackendConfig has no stable JSON representation.
 type BackendConfig struct {
+	// ID is the local backend identity within its resource list.
+	ID string
 	// Endpoint is the required absolute HTTP(S) base URL after all layers merge.
 	Endpoint *string
 	// APIKeyEnv optionally names an environment variable, not a credential.
@@ -71,15 +73,16 @@ type AuthenticationProbeConfig struct {
 	Endpoint *string
 }
 
-// BackendSource creates a labeled ConfigKit mapping from keyed backend values.
+// BackendSource creates a labeled ConfigKit mapping containing backend records
+// in caller order. IDs are explicit and duplicates are left for loading to reject.
 // It encodes fields without validating them; NewEngine validates the final
 // effective configuration after all selected source layers are combined.
 // Mapping captures a copy of supported input values at creation; unsupported
 // values fail when the source is loaded.
-func BackendSource(label string, backends map[string]BackendConfig) configkit.Source {
-	definitions := make(map[string]any, len(backends))
-	for id, config := range backends {
-		fields := make(map[string]any)
+func BackendSource(label string, backends []BackendConfig) configkit.Source {
+	definitions := make([]any, 0, len(backends))
+	for _, config := range backends {
+		fields := map[string]any{"id": config.ID}
 		if config.Endpoint != nil {
 			fields["endpoint"] = *config.Endpoint
 		}
@@ -119,7 +122,7 @@ func BackendSource(label string, backends map[string]BackendConfig) configkit.So
 			}
 			fields["smoke_tests"] = smokeTests
 		}
-		definitions[id] = fields
+		definitions = append(definitions, fields)
 	}
 	return configkit.Mapping(label, map[string]any{"backends": definitions})
 }