Roll back failed dynamic descriptor builds

internal/engine/schema.go

@@ -113,6 +113,7 @@ func buildSchema(root reflect.Type, secrets SecretBinding) (*schemaDescriptor, *
 type schemaBuilder struct {
 	cache    map[reflect.Type]*typeDescriptor
 	building map[reflect.Type]bool
+	journal  []reflect.Type
 	secrets  SecretBinding
 }
 
@@ -122,6 +123,7 @@ func (b *schemaBuilder) describe(current reflect.Type, path Path) (*typeDescript
 	}
 	descriptor := &typeDescriptor{typeOf: current}
 	b.cache[current] = descriptor
+	b.journal = append(b.journal, current)
 	b.building[current] = true
 	defer delete(b.building, current)
 
@@ -210,6 +212,13 @@ func (b *schemaBuilder) describe(current reflect.Type, path Path) (*typeDescript
 	return descriptor, nil
 }
 
+func (b *schemaBuilder) rollback() {
+	for _, current := range b.journal {
+		delete(b.cache, current)
+	}
+	b.journal = nil
+}
+
 func (binding SecretBinding) validate() {
 	if binding.Type == nil {
 		return