Improve screen reader accessibility with accessible mode and keyboard navigation

[thienautran]

I propose adding accessible mode, F6 navigation between the main areas of T3 Code, and arrow navigation in the Threads sidebar. These would help keyboard and screen reader users move around the web and desktop apps without tabbing through every control. Accessible mode should be part of the initial implementation so later accessibility features can use the same setting.

VS Code already implements this approach. The documentation and source show how it works:

• Microsoft's accessibility guide recommends F6 and Shift+F6 for moving between areas of the app. Its Tab navigation guidance also recommends these keys for moving between webview previews and the rest of the app.
• The F6 command registrations bind F6 to Focus Next Part and Shift+F6 to Focus Previous Part. Both commands also appear in the command palette.
• The area navigation code identifies the area that has focus, follows a defined order in either direction, and skips hidden panels.
• The focus handler then calls the active editor or view's focus method in the chosen area.
• VS Code's list navigation commands bind Up and Down to movement between rows. Home and End move to the first and last rows. In trees, Left collapses a group or moves to its parent, while Right expands a group or moves to its first child. Enter selects the focused item.
• VS Code's screen reader mode offers Auto, On and Off. Its accessibility service combines that preference with detected screen reader support. Its desktop service gets that detection state from the desktop window.

For T3 Code, I propose the following keyboard behavior. The area order adapts VS Code's approach to T3 Code's layout.

Key	Where it applies	What it does
F6	Main workspace areas	Move to the next visible area. After the last area, return to the first.
Shift+F6	Main workspace areas	Move to the previous visible area, in the opposite order.
Tab / Shift+Tab	Controls within an area	Move to the next or previous control. In the sidebar, enter or leave the row list instead of tabbing through every thread.
Up / Down	Threads sidebar row list	Move focus to the previous or next visible row without opening a different thread.
Right Arrow	Threads sidebar row list	Expand the focused group. If it is already expanded, move focus to its first child.
Left Arrow	Threads sidebar row list	Collapse the focused group. If it cannot be collapsed, move focus to its parent group when one exists.
Home / End	Threads sidebar row list	Move focus to the first or last visible row.
Enter	Threads sidebar row list	Open the focused thread or toggle the focused group.

The proposed F6 order is the Threads sidebar, the conversation, the message input, then any open panels. Include the terminal when it is visible. Skip hidden areas. If a panel is maximized, include only the areas still available.

When you return to an area, focus should return to the control you last used. If that control is gone, focus should move to the area's default starting point. If a dialog is open, F6 must not move focus outside it.

Sidebar arrow keys should apply only while the row list has keyboard focus. When someone is searching or renaming a thread, arrows must keep moving the text cursor. Moving focus between rows should leave the current conversation open until Enter activates another thread. Screen readers should announce each row's name, whether it is the current thread, and whether a group is expanded or collapsed.

Screen readers should announce the name of the area you enter. A visible focus indicator should show keyboard users where they are. Users should be able to change the area-navigation shortcuts in Settings. Where a browser uses F6 for its own navigation, provide another shortcut that works inside T3 Code.

Accessible mode should be available in Settings and the command palette from the start:

Setting	What it does
Auto	Use screen reader detection where the client supports it. Make this the default.
On	Enable the screen reader features even when automatic detection is unavailable.
Off	Disable the extra screen reader features. Keep keyboard navigation and accessible labels available.

The first use of accessible mode would be short navigation hints for the sidebar and workspace areas. It should also give later features, such as reading chat responses or terminal output, a shared way to check whether screen reader features are enabled.

Store the preference for the client someone is using. A browser and the desktop app can connect to the same remote server while needing different settings. Where automatic detection is unavailable, users should be able to choose On. Changing the mode should take effect without restarting the app.

Moving between chat messages and subagent threads would come in later changes.

Screen reader testing should cover NVDA, JAWS and VoiceOver where possible, on both web and desktop.

These screen readers are also listed in VS Code's screen reader documentation.