Follow-up on #13726 from blitz feedback: Up/Down history cycling should only trigger when the caret is at the start/end boundary (or the input is empty).\n\nPreviously useInputHandlers intercepted arrows whenever inputBuf was empty, which still stole Up/Down from normal multiline editing. textInput now publishes caret position through inputSelectionStore even with no active selection, and useInputHandlers gates history/queue cycling on those boundaries.