Terminal output renders garbled on wide/complex TUI content (Windows/WebView2, tiled mixed-repo terminals)

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Summary

Worktree terminal output renders garbled / column-misaligned on wide or complex TUI content (markdown tables, box-drawing, wide Claude Code output). The garble can also re-render into a different misaligned state on its own, with no user input. Reproduced on a clean 0.1.21 install.

Environment

• Agent Workspace 0.1.21 (fresh Windows NSIS install)
• Windows 11, desktop app (Tauri / WebView2)
• Mixed-repo workspace with several tiled worktree terminals (5 worktrees, agent+server pairs)
• xterm.js 5.3.0 (loaded from CDN)

Symptoms

• Wide/complex output (tables, box-drawing) renders with misaligned columns / broken layout.
• Historically it "cleaned up" when scrolling the terminal up and back down (i.e. a repaint fixed it).
• It can spontaneously re-render into a different garbled state — not user-triggered — consistent with a re-fit/reflow happening in the background.
• The auto-heal from fix: auto-heal terminal PTY/grid desync (garbled TUI output in worktree terminals) #1003 does not resolve it, and the spontaneous re-render is not auto-heal fixing it.

Possible contributing factors (investigated, not confirmed as root cause)

1. Renderer fallback to DOM. client/terminal.js (and client/commander-panel.js) pass rendererType: 'canvas', but xterm 5.x removed that option, so terminals fall back to the DOM renderer — which is prone to leaving damaged rows unrepainted until a scroll forces a redraw. That matches the "fixes on scroll" behaviour. (PR fix: use Canvas renderer for terminals so output isn't intermittently garbled #1011 loads the Canvas renderer addon for this; unclear whether it also fixes the wide-content column misalignment, which looks more like a sizing/wrapping problem than a repaint one.)
2. PTY size vs rendered grid mismatch. The "columns don't line up / jumps on its own" pattern is consistent with the PTY's cols/rows disagreeing with the actual rendered grid width, so the agent wraps at the wrong column. The auto-heal re-fit (client/terminal.js, ~15s interval + on focus/visibility change) may itself re-wrap content into a new (still-wrong) state, which would explain the spontaneous "jumping."
3. Environment-specific. Windows 11 + WebView2 + a tiled multi-terminal grid; possible fit/measurement timing issues when many terminals share the grid and get resized together.

Best-effort repro

1. Open a mixed-repo workspace with several tiled worktree terminals on Windows (WebView2 build).
2. Have an agent emit wide/complex output (a markdown table or a boxed TUI).
3. Observe misaligned columns; note the layout can change on its own after a few seconds (around the auto-heal interval).

Notes

Happy to gather more detail if useful — e.g. which xterm renderer is actually active at runtime, and the PTY cols/rows vs the terminal element's measured width at the moment of garbling. Filing this from field experience where I couldn't reliably reproduce it outside the packaged Windows/WebView2 build, so a maintainer with more environments may be able to pin the exact cause.