Copy a code block by clicking the icon in its border

[shellicar]

Summary

• A code block carries a copy icon in its top border, and clicking it puts the block's source on the clipboard.
• Every sealed block carries one on its header, so a whole response or thinking block copies in one click.
• An icon appears only once what it copies is finished: a closed fence, or a sealed block.
• The status bar confirms how many lines were copied, for two seconds.
• A click copies only when the press and release land on the same target, so dragging off cancels.
• Everything else the mouse does still reaches the terminal, including drag-select and modified clicks.