Function schedule_agent_zoom_mirror 

fn schedule_agent_zoom_mirror(
    store: Arc<Store>,
    agent_id: String,
    zoom: Option<f64>,
)

Debounced trailing mirror of an agent block’s term:zoom into the per-agent ui:zoom content blob. zoom = Some(z) upserts; zoom = None (term:zoom reset to null / 1.0) deletes the row so a default agent persists nothing.