Chinese input renders as blank for a single CJK character in VSCode integrated terminal

Description

Chinese input renders as blank for a single CJK character in VSCode integrated terminal

Environment

• OS: Ubuntu 20.04

• VSCode: 1.132.0

• Terminal: VSCode integrated terminal

• $TERM: xterm-256color

• pi: 0.84.1

• opencode: 1.17.18

• Input method: Fcitx

• XMODIFIERS: @im=fcitx

• GTK_IM_MODULE: fcitx

• QT_IM_MODULE: fcitx

• Locale: en_US.UTF-8

Problem

When using pi or opencode interactively inside the VSCode integrated terminal, a single Chinese/CJK character is rendered as blank.

For example:

Input:
你
Result:

[blank]

However, if multiple Chinese characters are entered in the same input operation, they are rendered correctly:

你好   -> works

你你   -> works

But entering the characters separately does not work:

你     -> blank

你     -> blank

Other combinations also show the same problem:

你a    -> the Chinese character is blank

a你    -> the Chinese character is blank

Reproduction

1. Open a VSCode integrated terminal.

2. Start pi:

pi

3. Use a Chinese input method and enter a single character:

你

4. The character is not visible / appears as blank.

Entering multiple CJK characters in one operation works:

你好

Important observations

I tested several other programs in the same VSCode integrated terminal.

cat

cat

Input:

你

Result: works correctly

Python

python3 -c 'import sys; print(sys.stdin.read().encode())'

Input:

你好世界

Result:

b'\xe4\xbd\xa0\xe5\xa5\xbd\xe4\xb8\x96\xe7\x95\x8c\n'

The UTF-8 input is received correctly.

nano

nano /tmp/test.txt

Input:

你

Result: works correctly

vim

vim /tmp/test.txt

Input:

你

Result: works correctly

pi via stdin

printf '你' | pi

Result: works correctly

This suggests that pi can correctly process the UTF-8 character itself. The problem appears specifically during interactive TUI input.

TTY configuration

VSCode terminal:

TERM=xterm-256color

stty -a shows:

cs8

iutf8

icanon

echo

isig

and the same basic configuration is present in the normal system terminal.

Fcitx test

I also tested without the Fcitx-related environment variables:

env -u XMODIFIERS -u GTK_IM_MODULE -u QT_IM_MODULE pi

The problem remains:

你 -> blank

Therefore, simply removing the Fcitx environment variables does not resolve the issue.

Comparison

The issue appears to be specific to interactive TUI applications such as pi and opencode:

Suspected cause

The issue seems related to interactive TUI input/rendering of a single CJK character, possibly involving Unicode grapheme width, cursor positioning, incremental redraw, or terminal input handling.

The fact that:

你       -> blank
你好     -> works
你你     -> works

suggests that the problem may occur specifically when the TUI performs an incremental redraw after receiving a single CJK character.

It does not appear to be a general UTF-8, locale, Fcitx, VSCode terminal, or font rendering problem, since the same terminal correctly handles Chinese input in cat, nano, vim, and Python.

Could you please help determine whether this is a known issue in the TUI/input rendering layer, and whether there is a workaround or configuration to fix it?

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

No response

Terminal

No response