Preedit text should support multiple lines of input

[1dancook]

Description

Typing Japanese in a pre-completed state doesn't wrap around when it should. Instead, the pre-completed text is truncated and remains on the same line. The effect is that you can only see a portion of what is typed, which makes it difficult to see what has been typed and additionally difficult to use several completion selections.

Example

I've recorded a short video. On the left is textedit, on the right Ghostty. The normal behavior in apps is for Japanese to wrap while typing as seen in textedit (with wrapping turned on). (Ignore the completion window getting annoyingly in the way!)

japanese-input-ghostty.mov

Version

Ghostty: ffc4c6e
MacOS 15.0.1

Other

I have seen another issue with Japanese input (just having one character displayed). It only seems vaguely related so I'm not linking it. I suspect this issue affects other languages that require IME + completion but I haven't tried to test those.

[mitchellh]

The preedit is limited to one line. You can make the window wider to support longer pre-edits. This is an intended limitation right now. I think the preedit should be expanding farther to the left to take up the full line if possible but it explicitly doesn't support multiple lines right now.

I've changed the title and tags to reflect this.