Integrated terminal: wide/fullwidth Unicode characters advance cursor by 1 column instead of 2

[tig]

Summary

The terminal emulator in GitHub Copilot does not correctly advance the cursor for wide (fullwidth) Unicode characters. Characters that should occupy 2 terminal columns (emoji, CJK ideographs, fullwidth forms) only advance the cursor by 1 column, causing all subsequent content on the line to shift left. This breaks grid alignment and causes display "tearing" in any TUI application that uses wide characters.

Steps to Reproduce

1. Open the integrated terminal in GitHub Copilot
2. Paste this into the terminal:

printf '\u250c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u252c\u2500\u2500\u2510\n'
printf '\u2502\U0001f600\u2502\U0001f601\u2502\U0001f602\u2502\U0001f923\u2502\U0001f604\u2502\U0001f605\u2502\U0001f606\u2502\U0001f607\u2502\n'
printf '\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\u2500\u2500\u2502\n'
printf '\u2514\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2534\u2500\u2500\u2518\n'

Or run the full repro app:

git clone https://github.com/gui-cs/Terminal.Gui.git
cd Terminal.Gui/Examples/WideCharRepro
dotnet run

Expected Behavior

Each wide character occupies exactly 2 terminal columns. The grid separators are vertically aligned and the X markers all appear at column 20.

Actual Behavior

Wide characters only advance the cursor by 1 column. Grids are misaligned, text overlaps, and the display is "torn."

Screenshot (GitHub Copilot terminal)

Terminal Comparison

All tests pass on every other terminal tested -- only the GitHub Copilot terminal fails:

Terminal	OS	Result
Ghostty	macOS	PASS
GitHub Copilot (terminal)	macOS	FAIL
GitHub Copilot (terminal)	Windows	FAIL
iTerm2	macOS	PASS
Kitty	macOS	PASS
Terminal.app	macOS	PASS
Visual Studio 2026	Windows	PASS
VS Code Insiders	Windows	PASS
Windows Terminal	Windows	PASS

Impact

This makes any TUI application that renders wide characters unusable in the GitHub Copilot terminal. Affected applications include:

• Terminal.Gui -- cross-platform .NET TUI toolkit (CharMap scenario is completely broken)
• Any ncurses/curses-based application using CJK or emoji
• tmux, vim, htop, etc. when displaying wide characters

Technical Details

The terminal must use the Unicode East_Asian_Width property (or an equivalent wcwidth implementation) to determine how far to advance the cursor after printing each character. Characters with East_Asian_Width = W (Wide) or F (Fullwidth) require 2 columns.

Affected Unicode ranges:

• Emoji (U+1F600-U+1F64F, U+1F900-U+1F9FF, etc.)
• CJK Unified Ideographs (U+4E00-U+9FFF)
• CJK Compatibility Ideographs (U+F900-U+FAFF)
• Fullwidth Forms (U+FF01-U+FF60)

Relevant standards:

• Unicode TR#11 -- East Asian Width
• POSIX wcwidth(3)
• Unicode TR#51 -- Emoji Presentation

Environment

• OS: Windows 11 24H2 / macOS (both affected)
• Terminal: GitHub Copilot integrated terminal
• Shell: PowerShell 7.5
• Font: Default (Copilot terminal font)