diff --git a/internal/usecase/smoke_selection.go b/internal/usecase/smoke_selection.go
index 0bd91df..cfc99c4 100644
--- a/internal/usecase/smoke_selection.go
+++ b/internal/usecase/smoke_selection.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"net/url"
-	"strings"
 
 	"gitea.maximumdirect.net/eric/promptkit/internal/defaults"
 	"gitea.maximumdirect.net/eric/promptkit/internal/domain"
@@ -36,15 +35,12 @@ func (r *Runner) resolveSmokeTestTarget(ctx context.Context, req domain.SmokeTes
 		return nil, fmt.Errorf("%w: %w", ErrInvalidRequest, err)
 	}
 
-	promptID := strings.TrimSpace(req.PromptID)
-	profileID := strings.TrimSpace(req.ProfileID)
-	backendID := strings.TrimSpace(req.BackendID)
-	if promptID == "" && strings.TrimSpace(req.PromptVersion) != "" {
+	if req.PromptID == "" && req.PromptVersion != "" {
 		return nil, fmt.Errorf("%w: prompt version requires a prompt id", ErrInvalidRequest)
 	}
 
 	var promptInspection *domain.PromptInspection
-	if promptID != "" {
+	if req.PromptID != "" {
 		promptInspection, err = r.resolvePromptInspection(ctx, req.PromptID, req.PromptVersion)
 		if err != nil {
 			return nil, err
@@ -54,13 +50,13 @@ func (r *Runner) resolveSmokeTestTarget(ctx context.Context, req domain.SmokeTes
 	selection := &smokeTestSelection{transientRetries: transientRetries}
 	var selectedProfileID string
 	switch {
-	case profileID != "":
+	case req.ProfileID != "":
 		selectedProfileID = req.ProfileID
 		selection.target.SelectionSource = smokeSelectionSourceProfile
 	case promptInspection != nil && (promptInspection.DefaultProfileID != "" || isInferenceSmokeTest(req.Kind)):
 		selectedProfileID = promptInspection.DefaultProfileID
 		selection.target.SelectionSource = smokeSelectionSourcePrompt
-	case backendID != "" && isInferenceSmokeTest(req.Kind):
+	case req.BackendID != "" && isInferenceSmokeTest(req.Kind):
 		backend, err := r.resolveSmokeBackend(req.BackendID)
 		if err != nil {
 			return nil, err
@@ -72,7 +68,7 @@ func (r *Runner) resolveSmokeTestTarget(ctx context.Context, req domain.SmokeTes
 		selection.backend = backend
 		selection.target.DefaultSourceBackendID = backend.ID
 		selection.target.SelectionSource = smokeSelectionSourceBackendDefault
-	case backendID != "":
+	case req.BackendID != "":
 		backend, err := r.resolveSmokeBackend(req.BackendID)
 		if err != nil {
 			return nil, err
diff --git a/internal/usecase/smoke_selection_test.go b/internal/usecase/smoke_selection_test.go
index c6becf1..84afb33 100644
--- a/internal/usecase/smoke_selection_test.go
+++ b/internal/usecase/smoke_selection_test.go
@@ -262,6 +262,27 @@ func TestResolveSmokeTestTargetSelectionAndSettingsErrors(t *testing.T) {
 			},
 			wantErr: ErrProfileLoad,
 		},
+		{
+			name: "invalid prompt selection does not fall back",
+			request: domain.SmokeTestRequest{
+				Kind: domain.SmokeTestTextInference, PromptID: "missing.prompt", BackendID: "epsilon",
+			},
+			wantErr: ErrPromptLoad,
+		},
+		{
+			name: "blank explicit profile does not fall back",
+			request: domain.SmokeTestRequest{
+				Kind: domain.SmokeTestTextInference, ProfileID: " ", BackendID: "epsilon",
+			},
+			wantErr: ErrInvalidRequest,
+		},
+		{
+			name: "version cannot be supplied without prompt",
+			request: domain.SmokeTestRequest{
+				Kind: domain.SmokeTestTextInference, PromptVersion: " ", BackendID: "epsilon",
+			},
+			wantErr: ErrInvalidRequest,
+		},
 		{
 			name:    "dangling backend default fails only when selected",
 			request: domain.SmokeTestRequest{Kind: domain.SmokeTestTextInference, BackendID: "delta"},