a11y(focus): Ctrl/Cmd+Shift+L global shortcut to focus the chat input

[pjdoland]

Summary

Keyboard-first users had no shortcut to land focus on the NBI chat prompt. Reaching it required clicking the side-panel tab and then tabbing past every intervening control in the sidebar.

Solution

Register a JupyterLab command notebook-intelligence:focus-chat-input bound to Accel Shift L (Ctrl+Shift+L on Linux/Windows, Cmd+Shift+L on macOS). The handler activates the NBI sidebar via app.shell.activateById(panel.id) and dispatches a copilotSidebar:focusPrompt CustomEvent. The React sidebar listens for the event and focuses promptInputRef.current, retrying across up to 10 animation frames so the cold-collapsed-sidebar case (multi-frame mount) still lands.

Using a CustomEvent instead of document.querySelector('#sidebar-user-input textarea') matches the existing copilotSidebar:runPrompt / copilotSidebar:activeDocumentChanged / copilotSidebar:addOutputContext pattern, keeps the command handler decoupled from the DOM id, and lets the React side use the ref it already owns.

Also added to the command palette under "Notebook Intelligence" for discoverability.

Testing

• jlpm tsc --noEmit clean. jlpm lint:check clean. jlpm jest 181 passed.
• Six-reviewer pass replaced the original querySelector + single-rAF approach with the CustomEvent + multi-frame retry pattern.

Risks / follow-ups

• The shortcut applies globally (selector: 'body'). The JupyterLab command-registry shortcut model lets users remap or remove it via their keyboardShortcuts settings.
• A Galata regression test that presses the binding and asserts focus lands on the textarea is deferred.
• Other NBI activate-panel sites use tabsmenu:activate-by-id instead of activateById; worth aligning in a follow-up for consistency.
• No tracked GitHub issue; audit identifier (D021) is internal.