Teams bot framework - composeExtensions does not display buttons on adaptive card

Question

Two compose extension commands are defined in the manifest. These trigger a request to bot framework, which responds with an adaptive card.

When the adaptive card is displayed, it's rendered correctly except the button is missing. If I send the exact same adaptive card as a chat activity, it displays correctly.

handleTeamsMessagingExtensionFetchTask Code

// enableInboundCard = below json
const card = this.renderAdaptiveCard(enableInboundCard, { channel })

    return {
      task: {
        type: 'continue',
        value: {
          card,
          height: 500,
          title: 'Enable Inbound',
          width: 600
        }
      }
    };

Command (in manifest).

{
  "id": "enableInbound",
  "context": [
    "compose"
  ],
  "description": "Enable inbound SMS to channel",
  "title": "Enable Inbound",
  "type": "action",
  "fetchTask": true,
  "parameters": [
    {
      "name": "test",
      "title": "test",
      "inputType": "text",
      "value": "test"
    }
  ]
}

Adaptive Card

{
    "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
    "type": "AdaptiveCard",
    "version": "1.5",
    "body": [
        {
            "type": "TextBlock",
            "size": "Large",
            "weight": "Bolder",
            "wrap": true,
            "style": "heading",
            "text": "Enable Inbound SMS"
        },
        {
            "type": "TextBlock",
            "text": "A wholeeeeeeee bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch bunch  of txt",
            "wrap": true
        },
        {
            "type": "FactSet",
            "facts": [
                {
                    "title": "Current Channel",
                    "value": "${channel}"
                }
            ]
        },
        {
            "type": "ActionSet",
            "actions": [
                {
                    "type": "Action.Execute",
                    "title": "Enable Inbound SMS",
                    "verb": "enable_inbound",
                    "fallback": "Action.Submit"
                }
            ]
        }
    ]
}