Copying from CLI pastes PREVIOUS clipboard item.

### Describe the bug

If I have anything stored in my clipboard (E.g. "Some already copied text"), the act of highlighting and copying additional text withing the CLI pastes the PREVIOUSLY copied text into the input.

### Affected version

GitHub Copilot CLI 1.0.36.

### Steps to reproduce the behavior

1. Copy some text to store it in clipboard (E.g. "Previously copied text")
2. Select text from within the Copilot CLI (E.g. "Some new text")
3. Copy it (whether with `Ctrl + C`, `right-click`, etc.) - DO NOT PASTE ANYTHING
4. "Previously copied text" gets pasted into the input (THIS IS THE BUG)
5. (extra step, added verification) Now actually paste (`Ctrl + V`, second `right-click`, etc.) - "Some new text" gets added to input (added on top of previous, erroneous, pasted text).

### Expected behavior

Just copy what I copy - DON'T PASTE OLD ITEMS WHEN NOT INSTRUCTED TO PASTE ANYTHING.
ALSO, DON'T PASTE ANYTHING WHEN JUST COPYING!!!

### Additional context

_No response_

Start by reproducing the copy sequence in GitHub Copilot CLI 1.0.36: copy existing text, select and copy new text in the CLI, then observe the input before pasting. Trace the CLI's clipboard and selection handling; done means copying changes only the clipboard and never inserts the previous or newly copied item into the input.

索引モデルが issue の本文から書いたものです。