Function transition_worker_to_running 

fn transition_worker_to_running(
    workspace: &Arc<Workspace>,
    project_key: &ProjectKey,
    session_key: &SessionSlot,
    result: TagWriteResult,
)

Shared transition: flip a worker’s status to Running, update needs_tag according to the tag-write outcome, and emit WorkerStatusChanged { StatusChanged }. Idempotent.