Desktop app: line breaks a plugin inserts into the prompt box turn into spaces once you start typing

Where: Claude desktop app, Code tab, Claude Code 2.1.295, macOS.

What happens: A plugin calls $.prompt.fill({ text: 'first line\n\n---\n\nsecond line', mode: 'append' }). The prompt box shows the line breaks correctly. As soon as the user types a character, every inserted line break becomes a space, so the text reads first line --- second line. Trailing blank lines from a fill (used to put the cursor on a fresh line) are dropped the same way.

Expected: inserted line breaks stay as line breaks while the user edits, just as line breaks typed by hand with Shift+Enter do in the same box.

Steps:

1. Load a mod with a button that calls $.prompt.fill with text containing \n.
2. Press it in the desktop app. The line breaks render.
3. Type any character. The line breaks become spaces.

Workaround in use: the mod inserts single-line text on the desktop.