Seed isolated evaluation routes through the trusted system layer

Why: Upstream now reserves model and mock settings for system authority.

Evidence: Complete merged Backend suite and live resource/cap guards pass.

Impact: Fixture-only startup configuration, same effective route and profile; no further paid calls.

Refs: Upstream scoped settings contract; U2/U3 evaluation

internal/server/work_checkpoint_eval_test.go

@@ -142,9 +142,10 @@ func TestServeWorkCheckpointEval(t *testing.T) {
 		config["models"] = map[string]any{"chat": route}
 		modelRoute = route
 	}
-	if e = st.MergeSettingsScope(store.OwnerDefault, settings.ScopeUser, config); e != nil {
-		t.Fatal(e)
-	}
+	// The isolated fixture owns its startup configuration; managed model/mock
+	// settings use the same trusted system layer as production bootstrap.
+	settingSvc := settings.NewService(st)
+	settingSvc.SetSystemOverride(config)
 	prof := profiles.New(st)
 	if e = prof.EnsureDefault(); e != nil {
 		t.Fatal(e)
@@ -161,7 +162,6 @@ func TestServeWorkCheckpointEval(t *testing.T) {
 	b := bus.New()
 	registry := tools.NewRegistry()
 	registry.RegisterBuiltin()
-	settingSvc := settings.NewService(st)
 	library, err := prompts.DefaultLibrary()
 	if err != nil {
 		t.Fatal(err)