Plugin composer pills with a menu or popover now show an upward chevron at
every width, so a pill that opens a surface reads differently from a one-tap
action pill. Built-in Tasks and Subagents pills are unchanged.
The transcript's bottom inset used to be reserved only while some pill
existed. Plugins that add pills when a turn ends and remove them when the next
starts moved the transcript every turn. The inset is now reserved whenever the
agent has an active composer.