Use one execution plan throughout the runner

internal/app/planner.go

@@ -140,3 +140,22 @@ func BuildSingleStagePlan(name string) ([]stage.Stage, error) {
 	}
 	return []stage.Stage{s}, nil
 }
+
+// buildSingleStageExecutionPlan selects one canonical stage without applying
+// bounded-run prefix prerequisites. The run-stage family validates the stage's
+// concrete inputs and intentionally retains its established direct-execution
+// semantics.
+func buildSingleStageExecutionPlan(name string) (BoundedPlan, error) {
+	stages, err := BuildSingleStagePlan(name)
+	if err != nil {
+		return BoundedPlan{}, err
+	}
+	plan, err := BuildBoundedPlan(name, name)
+	if err != nil {
+		return BoundedPlan{}, fmt.Errorf("build stage plan: %w", err)
+	}
+	plan.stages = stages
+	plan.explicitFrom = false
+	plan.explicitThrough = false
+	return plan, nil
+}