Web messaging participant attributes missing in Architect inbound flow

Why are custom widget attributes not showing up in the inbound message flow context? I’m sending customAttr via the widget, but the Architect Data Action only sees platform metadata. The participant record doesn’t have it. Is there a specific endpoint I need to hit inside the flow to pull the interaction object instead? Here’s the current mapping attempt:

{
 "attributes": {
 "widgetData": "{{participant.attributes.customAttr}}"
 }
}

It comes back empty.

• check the widget config to ensure customAttr is actually in the sendAttributes array, otherwise it never leaves the client side.
• verify the Architect data action is pulling from {{interaction.participants[0].attributes}} instead of just {{participant.attributes}} since inbound web messaging contexts can be tricky with that scope.