Agent chat: a long tool output that wraps past eight rows collapses with Show more

Closed
TE
9d ago
+598-24

Leo's words (2026-10-22 21:28Z): "also the tool calling i think there should be more of like a "show more" type thing for long outputs or whatnot..."

Leo-ask: ask-c57e055a4e

What base already does

#23413 (merged 2026-10-21 15:59Z, after the 03960f5 nightly Leo's app runs) already collapses a tool block longer than eight lines:

  • its first eight lines show under a 28px bottom fade;
  • "Show all N lines" opens it in place, and "Show less" closes it;
  • the button is keyboard reachable, and Find in Chat opens the block.

That covers a call's output, a command's Shell block and an edit's diff.

The gap this fixes

The cap counted newlines only. Output wraps by default, so a result with a few long lines (a one-line JSON result, a minified log line) wrapped to dozens of rows with no cap and no toggle.

Change

  • A call's output and a Shell block whose few lines wrap past eight rows are now cut at eight rows the same way, with "Show more"; "Show less" closes them. Blocks cut by line count keep "Show all N lines".
  • The shipped look is #23413's, unchanged: same max-height, fade, button and strings.
  • "Show more" reuses the existing message.more string (21 locales, from #23431's long prompts). No new strings.
  • The new hook (useWrapsPast) lives in BlockParts.tsx. In ToolRow.tsx and ShellBlock.tsx only the usePreview inputs and the card's root attributes change; the <pre> lines that #23967 and #24030 edit are untouched.

Before / after (synthetic gallery fixtures, agent-pane.tool-output-collapse, Linux Chromium)

Before (base 4c3b775)After, collapsedAfter, Show more clicked
beforeafter collapsedafter expanded

Light: after light. The line-cut case is unchanged: lines

Live before/after: scripts/gallery-compare.sh ā†’ /compare/tp-tool-output-showmore/ on the gallery host (tailnet).

Versions tried (gallery experiment tool-output-collapse, Compare arms)

fade-link (shipped): 8 rows, bottom fade, text linksix-bar: 6 rows, fade, full-width quiet barten-chip: 10 rows, hard cut, corner chipfifteen-link: 15 rows, fade, link
fade-linksix-barten-chipfifteen-link

I picked fade-link because it is closest to Claude Code and the Codex app, which show a few lines and then a quiet "Show more" under the block. It is also the look #23413's line-cut blocks and #23431's long prompts already use, so the transcript keeps one collapse.

  • The chip covers the last visible line.
  • The bar is heavier than the row it serves.
  • Fifteen rows is a tall preview in a narrow pane.

The other arms stay in the gallery for comparison. Nothing changes for anyone by default beyond the wrapped-rows cut.

Performance

  • The collapse itself is CSS (the existing [data-preview="cut"] max-height, now var(--cv-preview-rows, 8)).
  • Rows are read only for a block that is drawn (an opened call), whose output has 8 or fewer lines, wraps, and has a line of 24 or more characters. A read is one scrollHeight plus one computed style, in a layout effect, when that block's own text, wrap or line count changes. No per-frame loop, and nothing per token for any other row.
  • Observer: one ResizeObserver on that block's own body, so a narrower or wider chat re-reads it. Stop condition and cleanup: it is disconnected when the block's text changes, when it stops wrapping or fits by line count, and when it unmounts.
  • No hot path changed for closed rows, so there is no before/after number.

Find

The text is drawn whole and only clipped, so Find counts it. A Find reveal bumps reveal, which opens the block, as for line-cut blocks (tested).

Tests

webviews/test/transcript-wrapped-output-preview.test.tsx covers:

  • cut with Show more, then Show less, with the control a real button that Find skips;
  • no toggle at 8 rows or fewer;
  • narrowing and widening re-read the block;
  • Wrap lines off is not cut;
  • the Shell block;
  • a Find reveal opens the block;
  • a whole block is never cut;
  • the experiment arm sets the rows;
  • the shipped arm still cuts at 8.

Observed / Not run

  • Ran on huge-blue at f3474b1:
    • the new file plus transcript-block-overflow, transcript-output-copy, permission-edit-diff, agent-pane-edited-card-expand and the shell tests: 57 pass, 0 fail;
    • gallery agent-pane-entries, manifest, play and play-names tests: pass;
    • vp fmt --check and vp lint on the changed files: clean;
    • type check: no errors in changed files;
    • acpmux-protocol check: pass.
  • Base findings, not from this PR:
    • gallery-coverage fails the same way at 4c3b775;
    • vp fmt --check flags src/pages/settings/components/HostSections.tsx;
    • CI reds are release-notary, Guard status and cmux-next checks (NO-SWIFTUI allowlist, Swift type-scale baseline, perf_gate_unlit). They are the same reds as #24030.
  • Not run: no Swift change, so no app compile is needed.

Changelog

Fixed: A long tool output whose lines wrap past eight rows now collapses with Show more in agent chats.

Agent session: cosmic-gray

šŸ¤– Generated with Claude Code