Function run_workflow 

pub async fn run_workflow(
    workflow: &Workflow,
    executor: &dyn Executor,
    work_dir: &Path,
    changeset_files: &[String],
    env: &HashMap<String, String>,
    tx: &Sender<StepResult>,
    engine: Option<&Arc<Engine>>,
    repo_id: Option<Uuid>,
    changeset_id: Option<Uuid>,
) -> bool

Run an entire workflow: stages sequentially, steps within parallel stages concurrently. Sends StepResults to tx as each step completes. Returns true if all required steps passed.

engine and repo_id are optional — when provided, the semantic step uses the full Engine-backed analysis. Pass None for both in tests or contexts without an Engine.