Agent View: Korean (CJK) characters ghost on left column after switching panes

Bug: Agent View — Korean (CJK) characters ghost on left column after switching panes

Summary

In Agent View mode, switching between agent panels leaves ghost characters on the leftmost column and breaks line wrapping. This happens only in Agent View — a regular single-session Claude Code window in the same terminal renders Korean (Hangul) text correctly.

Environment

• Claude Code: 2.1.141
• OS: Windows 11 Pro 26200 (10.0.26200.x)
• Terminal: Windows Terminal 1.24.10921.0
• Shell: PowerShell 7.6.1
• Font: D2Coding (fixed-width, CJK-aware)
• System ACP: 949 (cp949) — but [Console]::OutputEncoding = UTF8 is forced in PS7 profile
• TERM: xterm-256color
• FORCE_COLOR: 3
• CLAUDE_CODE_NO_FLICKER: not set

Symptoms

1. While in Agent View, when switching between agent panels (e.g. up/down arrow to focus a different agent), the leftmost column of the screen retains the first character of each previous line as a ghost. Example (Korean):

• Lines like "AC", "스", "즉", "됩", "[C", "단", "깔", "P=", "요", "트", "B" appear stacked vertically on the left edge.

1. Scrolling up/down inside an agent's transcript leaves the same kind of ghost trail.
2. Korean text in long lines wraps in unexpected positions — a single logical line gets broken into many very short visual lines, suggesting the wrap calculator is treating CJK characters as width-1 instead of width-2 at some code paths.
3. Pressing Ctrl+L redraws the screen and clears the ghosts (until the next pane switch).

Repro

1. Open Windows Terminal → PowerShell 7
2. cd into a project where Claude Code conversations contain Korean text (agent task titles, status lines, log messages in Korean)
3. Run claude and dispatch 2+ background agents whose names/output contain Korean
4. Enter Agent View
5. Switch between agent panels using arrow keys → observe ghosts on the leftmost column

What works

• A regular single-session Claude Code window in the same terminal/font setup renders Korean perfectly.
• Pressing Ctrl+L clears the artifacts (temporary fix).

What did not help

• Setting [Console]::OutputEncoding = [System.Text.Encoding]::UTF8 in PowerShell 7 profile
• D2Coding fixed-width font (CJK-glyph-aware)
• Windows Terminal options: antialiasingMode: grayscale, useAcrylic: false, padding
• experimental.rendering.forceFullRepaint, experimental.rendering.software (also: Windows Terminal 1.24 silently strips these keys from settings.json on save)

Hypothesis

Looks like an inconsistency between the string-width/wcwidth calculation used to lay out Agent View panes and the dirty-region tracking used when redrawing on pane switch. CJK characters seem to be sometimes accounted as width-1 (so dirty-region clears only one cell) and sometimes width-2 (so the second cell of the previous character is never overwritten on the leftmost column).

Screenshot

[user will attach screenshot here showing the Agent View ghost pattern]