TUI plugin slots — one verb: ui.slot(region, { placement, render })

// the host owns layout; <Region> resolves parts + claims into children.
// part ids are the published anchor vocabulary — coarse, few, stable.
<Region
  name="prompt.footer"
  input={{ sessionID: props.sessionID, mode: store.mode }}
  parts={[
    { id: "left",  parts: [{ id: "status", render: () => <LocationLabel /> }] },
    { id: "right", parts: [
      { id: "tokens", render: () => <TokenUsage /> },
      { id: "hints",  render: () => <KeyHints /> },
    ]},
  ]}
/>

<Region name="sidebar.footer" input={{}} parts={[{ id: "hint", render: () => <FocusHint /> }]} />