Short: Find bugs works on native tasks
Launching bug hunters on a native task failed with a tmux socket error, because the launch path always split a tmux pane. Hunters now open as real native panes through the shared backend-neutral pane API, stack in an equal column beside the agent's pane, get their prompt through the native pane, and leave keyboard focus with the main agent. A native launch that cannot open every hunter, lay the column out or deliver every prompt is rolled back and reported instead of half-starting — a pane that refuses to close is named rather than counted as gone — while tmux tasks are unchanged.