Remove superseded configuration loaders and consolidate runtime tests

appended_messages_contract_test.go

@@ -8,7 +8,6 @@ import (
 	"testing"
 
 	"gitea.maximumdirect.net/eric/promptkit"
-	"gitea.maximumdirect.net/eric/promptkit/testfixture"
 )
 
 func TestAppendedMessageRoleConstantsAreStrings(t *testing.T) {
@@ -30,15 +29,7 @@ func TestAppendedMessagesComposeFrozenEffectivePrompt(t *testing.T) {
 		{Role: promptkit.RoleUser, Content: "corrective request", CacheControl: cacheControl},
 	}
 	client := &fakeLLMClient{response: &promptkit.GenerateResponse{Content: "output"}}
-	engine, err := testfixture.NewEngine(
-		testfixture.Config{},
-		testfixture.WithPromptFS(contractPromptFS("prompt", "profile", "configured prompt"), "."),
-		testfixture.WithProfiles(testfixture.Profile{ID: "profile", Endpoint: "http://example.test/v1", Model: "model"}),
-		promptkit.WithLLMClient(client),
-	)
-	if err != nil {
-		t.Fatalf("construct engine: %v", err)
-	}
+	engine := newSimpleEngine(t, "configured prompt", promptkit.WithLLMClient(client))
 	request := promptkit.RunRequest{PromptID: "prompt", AppendedMessages: appended}
 
 	plain, err := engine.Prepare(context.Background(), promptkit.RunRequest{PromptID: "prompt"})