Use one execution plan throughout the runner

internal/app/runner_test_helpers_test.go

@@ -0,0 +1,15 @@
+package app
+
+import (
+	"context"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+	"gitea.maximumdirect.net/eric/narratio/internal/stage"
+)
+
+// executeStages keeps runner tests focused on controlled stage doubles. The
+// production command path always supplies one validated BoundedPlan directly.
+func executeStages(ctx context.Context, cfg *config.Config, stages []stage.Stage, opts RunOptions) (*RunSummary, error) {
+	plan := BoundedPlan{stages: append([]stage.Stage(nil), stages...)}
+	return executePlan(ctx, cfg, plan, opts)
+}