The mention popover owns the keyboard, and links open

Improved

• The @ mention popover and the / command popover now own the keyboard while they are open. Arrow keys wrap around instead of stopping at the ends, Home and End jump to the first and last row, PageUp and PageDown move by eight, and Tab accepts the highlighted row.
• The highlight no longer jumps back to the first row while you are arrowing through the list. It was reset whenever the row count changed, and the row list settles a moment after you type, so a quick arrow move could be undone.

Fixed

• Enter no longer sends the message while the mention popover is open. With the popover showing "No matches" or "Indexing files…" — or in the moment before the row list settles — Enter fell through to the send path, so a half-typed mention was sent as text.
• Clicking a link that opens in a new tab now works in the embedded browser. The opener plugin intercepted the click, called preventDefault(), and then had its own request refused, so the click was swallowed and nothing happened. A new tab now opens as expected.