[FEATURE] Desktop app: Tab should confirm @ file picker selection instead of moving focus to the next control

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

In the Claude Code desktop app, when I type @ in the chat input to reference a file and the file picker/autocomplete popup is open, pressing Tab does not confirm the highlighted suggestion. Instead, Tab follows the default web focus order and moves focus to the next button in the UI.

Tab-to-complete is the established convention everywhere else this pattern exists — the Claude Code CLI, VS Code, JetBrains, shells, and most autocomplete widgets. Muscle memory from those tools means I press Tab expecting to confirm the file, and instead I lose focus from the input and have to click or Shift+Tab back, often with the picker now dismissed.

Proposed Solution

While the @ file picker popup is open, Tab should accept the currently highlighted suggestion (same behavior as Enter), keeping focus in the message input so I can continue typing.

Normal Tab focus traversal should only apply when no autocomplete popup is open. (Same handling would make sense for the / command autocomplete for consistency.)

Alternative Solutions

• Pressing Enter confirms the selection, but Tab is deeply ingrained muscle memory from the CLI and IDEs, so I keep hitting Tab and losing input focus.
• Workaround today: notice focus jumped, Shift+Tab back into the input, reopen the picker.

Related (but distinct) issues found while searching: #32781 (@+TAB autocomplete erases typed text), #9338 (CLI: Tab reassigned to thinking mode broke filepath autocomplete), #72040 (@ picker highlight barely visible).

Priority

Medium - Would be very helpful

Feature Category

Other

Use Case Example

1. I'm in the Claude Code desktop app, typing a prompt about a specific file.
2. I type @ and the first few letters of the filename; the picker highlights the file I want.
3. I press Tab to confirm it (as I would in the CLI or any IDE).
4. Instead of inserting the file reference, focus jumps to the next button in the UI and I have to click back into the input and redo the mention.

With this feature, Tab would insert the highlighted file reference and leave my cursor in the input, so the desktop app matches the muscle memory from every other autocomplete.

Additional Context

_No response_