[Bug]: preview_press does not reliably target the preview page

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

1. Start T3 Code Desktop.

2. Open a Codex-backed thread with the T3 preview MCP tools available.

3. Open any page in the browser preview.

4. Install a page-level keydown listener:

   (() => {
     window.__t3KeyEvents = [];
     window.addEventListener(
       "keydown",
       (event) => {
         window.__t3KeyEvents.push({
           key: event.key,
           code: event.code,
           target: event.target && event.target.tagName,
           active: document.activeElement && document.activeElement.tagName,
           time: Date.now()
         });
       },
       true
     );
     return {
       active: document.activeElement && document.activeElement.tagName,
       events: window.__t3KeyEvents
     };
   })()
   

5. Confirm document.activeElement is BODY.

6. Call preview_press before clicking inside the page:

   { "key": "b" }
   

7. Read window.__t3KeyEvents.

8. Click inside the preview page body with preview_click.

9. Clear the log and call preview_press again:

   { "key": "c" }
   

10. Clear the log and call preview_press with Escape three times.

11. In a separate hidden or degraded tab, call preview_press with Tab, then call a simple preview_evaluate.

Expected behavior

preview_press should target the selected preview page consistently when a tabId is provided.

If the preview page is not focusable or the tab cannot receive keyboard events, the tool should return a clear failure. It should not return null while no key event reaches the page.

Keyboard events should not go to the T3 host prompt when the agent is trying to target the preview page.

Actual behavior

Before a real click inside the page, preview_press("b") returned null, but the page captured no key event:

{
  "active": "BODY",
  "events": []
}

After clicking the page body, preview_press("c") returned null and the page captured the event:

{
  "active": "BODY",
  "events": [
    {
      "active": "BODY",
      "code": "KeyC",
      "key": "c",
      "target": "BODY"
    }
  ]
}

After focus was established, three Escape presses all returned null, but only two page-side keydown events were captured.

In an earlier run, a printable key was not captured by the page and the human operator observed that the character appeared in the T3 prompt input instead.

On a previously degraded invisible tab, preview_press("Tab") timed out after 15 seconds, and a simple preview_evaluate immediately afterward also timed out.

Impact

Major degradation or frequent failure

Version or commit

T3 Code desktop 0.0.28-1 via t3code-bin AUR package.

Environment

Arch Linux x86_64, kernel 7.0.13-arch1-1, T3 Code desktop AppImage package via t3code-bin, Codex provider.

Logs or stack traces

Representative timeout after pressing in a degraded invisible tab:

PreviewAutomationTimeoutError: Preview automation press timed out after 15000ms.
PreviewAutomationTimeoutError: Preview automation evaluate timed out after 15000ms.

Screenshots, recordings, or supporting files

No screenshot included. Page-side key event logs are the relevant evidence. A recording could help demonstrate the host-prompt mutation, but the agent cannot inspect that host input directly.

Workaround

Before using preview_press, click inside the preview page and verify delivery with a page-side listener or an observable page effect. Avoid keyboard workflows in hidden or already-degraded tabs. Prefer preview_type for text input and preview_evaluate for state changes that are not specifically testing keyboard behavior.

Start by locating the preview_press entry point under apps/desktop and reproduce the documented key-event and degraded-tab cases. Compare delivery when tabId is supplied, after a page click, and in hidden tabs. Done means keys consistently reach the selected preview page or the tool returns a clear failure instead of null or an unexplained timeout.