Testing #145599 on macOS

clear doesn't flush the scrollback, which means, after running clear

• The decorations are gone, the cursor is now at the top of the terminal
• Run another command, the decoration shows at the very bottom of the scrollbar, which is different from initial creation of the terminal

Terminal just created, run a command

Terminal cleared, run a command

It seems this is because the scrollback is not really cleared, instead they are just pushed out of view (you can still scroll up to reveal the previous commands). Considering that the history is still in the buffer, it doesn't make sense to clear the decoration either.