Text fallback from agent not rendered in A2UI, page refreshes silently #585

When the agent fails to return data (e.g., no restaurants found, or max retries exhausted), the backend correctly sends a TextPart fallback message

Example backend log:

ERROR:agent:--- RestaurantAgent.stream: Max retries exhausted. Sending text-only error. ---

However, the frontend (A2UI) does not render this TextPart, and the UI appears to silently refresh or remain blank. Users never see the intended fallback message like:

Oops, I couldn’t find anything you requested.

Expected Behavior:
TextPart messages from the agent should be rendered in the UI, similar to how DataParts are displayed, so users see a clear error or fallback message.

Expected Behavior:
TextPart messages from the agent should be rendered in the UI, similar to how DataParts are displayed, so users see a clear error or fallback message.

Steps to Reproduce:

Query the agent with a request that triggers failure, e.g., “Chinese restaurants in Sydney” or any nonexistent location.

Observe the backend logs, which show a TextPart fallback message.

Observe the frontend: no message is displayed, and the page may refresh or remain blank.

Actual Behavior:

Backend sends the fallback TextPart.

Frontend fails to render it.

User sees no visible feedback.

Suggested Fix / Workaround:
Modify A2UI to handle TextPart messages and render them visibly. Example:

if (part.type === 'TextPart') {
const container = document.getElementById('fallback-container');
container.textContent = part.text;
container.style.display = 'block';
}