Add profile inheritance definition support

engine_test.go

@@ -2018,6 +2018,25 @@ func TestWithProfilesRejectsDuplicateIDs(t *testing.T) {
 	}
 }
 
+func TestWithProfilesAcceptsDerivedDefinitionWithoutTargetFields(t *testing.T) {
+	_, err := promptkit.NewEngine(promptkit.Config{PromptDir: frameworkPromptDir},
+		promptkit.WithProfiles(promptkit.Profile{
+			ID:            " derived-profile ",
+			BaseProfileID: " base-profile ",
+		}),
+	)
+	if err != nil {
+		t.Fatalf("derived profile should be accepted during construction: %v", err)
+	}
+
+	_, err = promptkit.NewEngine(promptkit.Config{PromptDir: frameworkPromptDir},
+		promptkit.WithProfiles(promptkit.Profile{ID: "standalone-profile"}),
+	)
+	if !errors.Is(err, promptkit.ErrInvalidConfig) {
+		t.Fatalf("standalone incomplete profile error = %v, want ErrInvalidConfig", err)
+	}
+}
+
 func TestWithProfilesRejectsInvalidExecutionSettings(t *testing.T) {
 	type testCase struct {
 		name    string
@@ -2170,6 +2189,7 @@ func TestOpenAICompatibleProfileMapsEveryField(t *testing.T) {
 	extraParams := map[string]any{"provider_option": "distinct-extra-params"}
 	got := promptkit.OpenAICompatibleProfile(promptkit.OpenAICompatibleProfileConfig{
 		ID:              "distinct-id",
+		BaseProfileID:   "distinct-base",
 		BackendID:       "distinct-backend",
 		Endpoint:        "https://distinct.example/v1",
 		Model:           "distinct-model",
@@ -2184,6 +2204,7 @@ func TestOpenAICompatibleProfileMapsEveryField(t *testing.T) {
 	})
 	want := promptkit.Profile{
 		ID:              "distinct-id",
+		BaseProfileID:   "distinct-base",
 		BackendID:       "distinct-backend",
 		Endpoint:        "https://distinct.example/v1",
 		Model:           "distinct-model",