Function EditShell

components/edit/EditShell/EditShell.tsx:74–118

({
  scene,
  leftRail,
  commandTrailing,
  rightRail,
  bottomRail,
}: EditShellProps)

 * the previous two-branch design caused (PR3a rearch).
 */
export function EditShell({
  scene,
  leftRail,
  commandTrailing,
  rightRail,
  bottomRail,
}: EditShellProps) {
  const surface = sceneEditorRegistry.resolve(scene.type) ?? NOOP_SURFACE;
  // Surface state is published from a child runner (keyed by sceneType so it
  // remounts when the surface identity changes — that's the boundary at which
  // rules-of-hooks naturally allows a different hook signature). The chrome
  // around it stays mounted and consumes state via these props.
  const [state, setState] = useState<SurfaceState | null>(null);
  const SurfaceComponent = surface.SurfaceComponent;

  return (
    <>
      {/* `key={scene.type}` is the remount boundary. We can't use
          `surface.sceneType` here because NOOP_SURFACE deliberately reuses
          'slide' as a placeholder (the SceneType union is closed and NOOP
          isn't a real type). The scene's own `type` is the actual signal
          that the hook signature inside `useSurfaceState` is about to
          change — so we remount the runner exactly when it does, keeping
          rules-of-hooks happy across the slide ↔ read-only surface swap
          while the rest of the chrome stays mounted. */}
      <SurfaceStateRunner key={scene.type} surface={surface} onChange={setState} />
      <Frame
        title={scene.title}
        leftRail={leftRail}
        history={state?.history}
        commands={state?.commands}
        trailing={commandTrailing}
        rightRail={rightRail}
        bottomRail={bottomRail}
      >
        <SurfaceComponent />
        {state?.insertItems && state.insertItems.length > 0 && (
          <FloatingInsertToolbar items={state.insertItems} />
        )}
        {state?.hasSelection && <FloatingToolbar actions={state.floatingActions} />}
        <HintRail hints={state?.hints} />
      </Frame>
    </>
  );
}

/**
 * Hidden runner that owns the surface state hook. `key={surface.sceneType}`