TUI trailing spaces break copy in xterm.js terminals (VS Code)

[Dombo]

What do you want to change?

Stop the renderer from appending trailing spaces, it already clears each line with \x1b[2K before writing so the trailing space serve no visual purpose they just pollute the clipboard.

Why?

Copying output from pi running in VS Code's integrated terminal includes trailing whitespace on every line, padding each line to the full terminal width.

xterm.js trims empty (unwritten) cells on copy but preserves real space characters. The TUI components (Markdown, Text, Box, TruncatedText) pad every rendered line to the terminal width with space characters. The renderer already clears each line with \x1b[2K before writing, so the trailing spaces serve no visual purpose — they just pollute the clipboard.

iTerm masks this with its own trim-on-copy. xterm.js-based terminals (VS Code, any Electron app) do not.

How? (optional)

Proposed Fix: #6248

[github-actions]

This issue was auto-closed. All issues from new contributors are auto-closed by default.

Maintainers review auto-closed issues daily and reopen worthwhile ones. Issues that do not meet the quality bar in CONTRIBUTING.md will not be reopened or receive a reply.

If a maintainer replies lgtmi on one of your issues, your future issues will stay open. If a maintainer replies lgtm, your future issues and PRs will stay open.

See CONTRIBUTING.md.

[github-actions]

Pi issue analysis finished.

Share URL: https://pi.dev/session/#8884fec57a7afb7abbb70bd0207549ff
Gist: https://gist.github.com/issuron/8884fec57a7afb7abbb70bd0207549ff

Continue locally from a checkout with:

pi "/ir 8884fec57a7afb7abbb70bd0207549ff"

Agent analysis summary

CI=true, so I did not add inprogress or assign the issue.

Issue analyzed: #6251

Read:

• TUI trailing spaces break copy in xterm.js terminals (VS Code) #6251 and comments
• linked PR fix: stop padding TUI lines with trailing spaces #6248 and diff
• related Copied TUI output includes trailing spaces and blank-line indentation #2033
• related Let us disable padding for assistant messages (and thinking) #6168 and merged PR Disable padding for assitant messages. #6169

Findings:

• This is a real bug/UX issue for xterm.js terminals.
• Text, Markdown, Box, and TruncatedText all render non-background lines padded to full terminal width with literal spaces.
• xterm.js treats those as written cells, so copy includes trailing spaces.
• I verified current output: simple renders at width 20 produce full-width strings ending in spaces.
• The renderer does clear changed lines with \x1b[2K on differential renders, but not every path:
  • initial fullRender(false) does not clear each line before writing
  • fullRender(true) clears the screen first
  • differential updates clear lines before writing
• So the issue’s statement is mostly true for differential rendering, but incomplete for initial render. A fix that only removes component padding can leave stale cells on first render if the terminal line was not clean.

Actual root cause:

• Padding responsibility is duplicated in leaf/container components instead of being handled by the renderer.
• For foreground-only lines, full-width literal-space padding is unnecessary after a cleared line and pollutes terminal copy buffers.
• For background-colored lines, padding is still needed unless the renderer uses a background-preserving erase-to-EOL strategy.

Proposed fix:

1. Stop padding foreground-only output in:
   • packages/tui/src/components/text.ts
   • packages/tui/src/components/markdown.ts
   • packages/tui/src/components/box.ts
   • packages/tui/src/components/truncated-text.ts
2. Keep full-width padding when a background function is active.
3. Make initial non-clearing full render safe by clearing each line before writing short lines, e.g. in packages/tui/src/tui.ts inside fullRender(false) write \r\x1b[2K before each line or otherwise guarantee column 0 + cleared line.
4. Add/update tests:
   • component tests asserting foreground-only lines are not right-padded
   • background tests asserting background lines remain full width
   • renderer test proving first render with short lines clears stale content
   • regression test using xterm/headless buffer cells if feasible

Affected files:

• packages/tui/src/components/text.ts
• packages/tui/src/components/markdown.ts
• packages/tui/src/components/box.ts
• packages/tui/src/components/truncated-text.ts
• packages/tui/src/tui.ts
• packages/tui/test/* for updated expectations/regression coverage

I would not take PR #6248 as-is without adding the renderer-side first-render safety test/fix.

[davidbrai]

looks similar to #2033 which mario said could break the TUI.

[Dombo]

I've been running my build of this branch for a few days without issue. I did see that comment he made but cannot see what the specific concern with TUI rendering we're worried will be disrupted.

Happy to amend PR

[Dombo]

Would you like me to implement the alterations proposed by the agent?