[Authoring] Templating doesn't support JSON keys with whitespace

Target Application

Teams, Copilot

Application Operating System

Windows

Schema Version

1.4

Problem Description

Given this card

{
    "type": "AdaptiveCard",
    "body": [
        {
            "type": "TextBlock",
            "text": "Product ${product}"
        },
        {
            "type": "TextBlock",
            "text": "Price ${unit price}"
        }
    ],
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "version": "1.6"
}

and this payload

{
    "product": "Widget",
    "unit price": "$42"
}

The card does not render at all in the designer. I could not find any documentation on the differences between property names as supported in the binding syntax vs. legal JSON key names. I tried a variety of escaping techniques with no success.

Expected Outcome

A way to bind to a JSON key that contains whitespace.

Actual Outcome

Card does not render in the designer
Value is rendered as "${unit price}" in Copilot

Card JSON

{
    "type": "AdaptiveCard",
    "body": [
        {
            "type": "TextBlock",
            "text": "Product ${product}"
        },
        {
            "type": "TextBlock",
            "text": "Price ${unit price}"
        }
    ],
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "version": "1.6"
}

Repro Steps

No response

Start by tracing the authoring templating and binding-syntax handling used by the designer, then compare it with the JSON payload and card examples in this report. Reproduce the whitespace-key case in the designer and Copilot; done means a JSON key such as "unit price" binds successfully and existing keys still render correctly.