Stale scrollback frames interleave with live region in Claude Code panes during CJK streaming (persists on 0.6.8)

[resodo]

Environment

• herdr 0.6.8 (Homebrew, stable channel), server and client both 0.6.8, protocol 12
• kitty 0.45.0
• macOS 26.5 (Darwin 25.5.0)
• Claude Code 2.1.170, zsh
• Content: heavy Chinese (double-width) text mixed with English

Symptom

In a long-running Claude Code pane, scrollback intermittently shows fragments of OLD frames interleaved with current content:

• struck-through task-list lines from Claude Code's footer widget (SGR 9) appear merged into unrelated earlier output lines;
• the -- INSERT -- auto mode on status line is duplicated 3-4 times at different scrollback positions;
• characters from two different render cycles concatenate within a single line (e.g. diff content + task-list title interleaved);
• CJK text occasionally splits/misaligns at the seams.

Ctrl+L (app repaint) or a window resize clears the live screen; already-baked scrollback stays corrupted.

When it triggers

Most reliably when several footer redraw sources coincide while the assistant is streaming large CJK output:

• Claude Code error banner redraws (API Error: ... ConnectionRefused during a network blip)
• Claude Code auto-update banner (update failed - Run /doctor)
• task-list footer updates (items completed -> strikethrough)

What I ruled out

• Upgraded 0.6.6 -> 0.6.8: the grapheme-cluster fixes and the [Bug] Claude Code session content duplicates in scrollback after reconnect #346 reconnect-duplication fix did NOT resolve this class; reproduced on both versions (confirmed the running server is 0.6.8 via herdr status server).
• Same Claude Code sessions render clean in bare kitty (no herdr).
• codex CLI panes (append-only output) never show it; only Claude Code's in-place live-region repaints do.
• Checked existing issues: [Bug] Claude Code session content duplicates in scrollback after reconnect #346 (reconnect duplication) and edit_scrollback drops UTF-8 lead bytes, corrupts multi-byte characters #324 (edit_scrollback UTF-8) describe different mechanisms; this happens live, without reconnect.

Guess

The pane VT/compositor occasionally mishandles Claude Code's cursor-jump live-region repaints under load, committing partial frames into scrollback; SGR state (strikethrough) leaks across the seams.

Screenshots from both 0.6.6 and 0.6.8 will be attached in a comment. Happy to test a preview build or collect a recording with whatever instrumentation helps.

[kangal-bot]

hi @resodo, thanks for opening this.

this issue does not appear to use the full bug report template. herdr issues are only for reproducible bugs and maintainer-created or maintainer-converted work items.

bug reports must include the reproducible-bug confirmation, current behavior, expected behavior, reproduction, impact, and environment fields with herdr version, operating system, and terminal.

feature requests, ideas, questions, contribution proposals, and direction checks belong in discussions:
https://github.com/ogulcancelik/herdr/discussions

please read the contributing guidelines before opening issues or prs:
https://github.com/ogulcancelik/herdr/blob/master/CONTRIBUTING.md

closing this so the issue tracker stays limited to actionable bug reports.