Panes and tabs can't be used from the keyboard, and overflowing tabs are hidden #621

Panes and tabs can't be driven from the keyboard, overflowing tabs are hidden, and nothing lists the shortcuts that do exist.

What was seen

• The "Resize columns" divider ignores arrow keys and has no slider role, so there's no keyboard or screen-reader way to resize (^640).
• At 700 px wide the single tab strip overflowed: "Terminal" was cut to "Te" under the host label and "Diff" was hidden "with no hint that it existed" (^644).
• No shortcut list anywhere: Settings has none, ⌘/ does nothing, and the only place keys appear is the right side of palette entries. "Notifications alt+T" exists only as a hidden region label (^660).
• ⌘T, ⌘W, ⌘⇧], Ctrl+Tab, ⌘\ and ⌘⌥← did nothing. Split right's tooltip shows no key, New tab has no tooltip, and the palette has no tab, split or pane actions (^661).
• The palette lists only tabs that aren't on screen. With two terminals visible, searching "Terminal 1" returned just the channel, and picking it moved focus to New tab (^765).

Steps

1. Split right, focus the divider, press ←/→.
2. Open Chat, Diff and two Terminals, narrow the window to 700 px.
3. ⌘K → "Terminal" with both terminals visible.

Expected: arrow keys move the divider, an overflow control for hidden tabs, a shortcut list, and every open tab in the palette.

Rig: web (loopback source host from origin/main, 0.0.53 code).

Map: ^640, ^644, ^660, ^661, ^765.

Found in the 2026-10-22 map study.