Host data bindings

Let surfaces show live app state, such as the cart total, without the value ever leaving the device.

A surface prop can be a binding { "path": "/host/cart/total" }. Paths under /host/ are resolved on the device against data your app publishes:

Kletso.instance.setHostData({
  'cart': {'items': 2, 'total': 3198, 'label': '₹302 away from free shipping'},
});
Kletso.instance.updateHostData({'cart': {'items': 3, 'total': 3897}});

setHostData replaces the whole map; updateHostData merges the top level.
Changing host data rebuilds rendered surfaces, so a progress block bound to /host/cart/progress moves as the user shops.
The values are never sent to the runtime or the model. If the model needs to know the cart value, put it in context instead.
Resolution order for /host/... paths: your host data first, then the surface’s own data as a fallback (so the model can ship a default). All other paths resolve against the surface data only.

Example surface node the agent might render:

"ship": { "type": "progress", "props": { "value": { "path": "/host/cart/progress" }, "label": { "path": "/host/cart/label" } } }

Renderers outside the chat can pass their own resolver: KletsoSurfaceView(surface: s, bindingResolver: myResolver).