Subagent-active indicator disappears when switching into the subagent's own transcript view

When a subagent is running, the main session window shows an indicator at the bottom that it's active. Navigating into the subagent's own transcript (e.g. via left-arrow) to check on/chat with it hides that indicator -- so if you're viewing the subagent's window, you lose the visual cue that it (or another subagent) is still working, and have to switch back to the main window to be reminded. It'd help if that status persisted (or was shown in some form) regardless of which window/transcript is currently focused, so it's not easy to lose track of active subagents while inspecting one of them.