PR #32805 - manaflow-ai/cmux

Leo, 2026-11-03, on a running "Monitor" tool row whose spinner sat at the transcript's far right edge, a whole column away from the row's words:

yo what the
this is kinda weird looking
doesn't claude desktop have the thinking shimmer go across stuff

A running tool row now shows that it runs on its own words, as Claude desktop's and ChatGPT's running rows do: a soft light band sweeps across the label while the call runs. Nothing is parked at the row's far edge.

Change

ShimmerText.tsx RowShimmer: the row's own words drawn again as an inert, aria-hidden lit copy over them. It reuses the Thinking line's two transform-only loops (cmux-shimmer-band / cmux-shimmer-lit, --cmux-shimmer-period 2.8 s, on the shared clock), so the Thinking line and running rows sweep together and the page paints nothing per frame. The band moves inside a still clip, so the label's box never grows and ToolRow's cut-label disclosure check is unaffected.
ToolRow and CommandRow draw it while the call runs, in the foreground or the background. It unmounts when the call ends, so the loop stops with it.
BackgroundMark: no spinner while a call runs in the background (this was the mark in Leo's screenshot). Its running state stays screen-reader text; the check, "Failed" and "Stopped" still show once it ends. The now-unused grouped / showActivity props are gone.
A running row's words rest at --cv-text-dim (a step under a finished row, as ChatGPT's in-flight row is) and the band lights them to --cv-text. Reduce Motion, data-cmux-motion off or reduced, and the static status look keep the dimmed words still, with no animation.
Not touched: the agent working-state mark (sidebar, tabs, subagent tray), which stays a spinner; tool group and run summary lines; Thinking; compaction. The "Monitor"/"TaskStop" raw names are already handled by #32738.

Gallery

agent-pane.tool-row-shimmer uses the real rows (a finished TaskStop, a background Monitor, a running read and command, a finished read) in six arms: shipped (the Thinking line's 40% band and 2.8 s clock, lit to the text colour), narrow (48 px band), wide (70%), quick (1.8 s), accent (the Thinking line's accent tint), and still (Reduce Motion). I chose shipped: it matches the references' few-letters-wide soft band in neutral text colour, and it stays in step with the Thinking line. The arms were captured mid-sweep in dark and light and compared with the references; captures are kept private.

References used (cmux-design-references): chatgpt/web/status-work-grouped-tool-rows, chatgpt/web/status-work-working-for-timer, claude/live/status-thinking-line-token-counts, and Leo's own cmux/live/transcript-running-tool-row-detached-spinner.

Design spec: leo-workspace design/chat-transcript.md (tool groups' spinner section), updated in a leo-workspace PR to match.

Measurements (same harness, `test/browser/tool-row-shimmer.html`, Chromium)

metric	before (base 4fbe098)	after
painted marks right of a running background row's words	1 (spinner)	0
spinners on running tool rows	1	0
running rows whose words shimmer	0 of 3	3 of 3
animations on a running row	1 (spin)	2 (band + lit, transform only)
animations on a finished row / under Reduce Motion or the motion gate	0 / 1	0 / 0
running words' colour (dark)	same as finished (white @ 0.58)	`--cv-text-dim`

Tests

New test/tool-row-shimmer-browser.test.ts (red/green): no spinner and no painted mark right of a running row's words; each running row's lit copy is its own words and runs cmux-shimmer-band; the words' box doesn't grow; a finished row has no shimmer; Reduce Motion and data-cmux-motion reduced and off run no animation and keep the words dimmed. Committed first: 4 fail on base (spinner: monitor), 4 pass on head.
BackgroundMark.test.tsx now asserts no spinner and an inert shimmer while running, and none once it finishes.
Ran on the fleet: the new test, tool-row-column-browser, transcript-row-spinners, BackgroundMark, agent-pane-background-tasks, transcript-collapsed-tool-runs: all pass.

Observed / Not run

Observed: the fleet Chromium runs above, and gallery captures of every arm mid-sweep in dark and light.
Not run: WebKit; a DEV build in the app.

Risk: low. The change is confined to the transcript's tool row components and their CSS. A running row's words are a step dimmer, and the band is CSS-only.

Changelog

Running tool calls in the agent chat shimmer across their own label, as in Claude desktop, instead of showing a spinner at the far edge of the transcript.

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Running tool rows in the agent transcript now shimmer across their own label instead of showing a spinner at the far edge, matching Claude desktop and ChatGPT.

Adds a RowShimmer overlay that reuses the Thinking line's existing band animation, so running rows sweep in step with it.
Removes the spinner from BackgroundMark while a background call runs; the running state stays as screen-reader text only.
Running words rest at --cv-text-dim; Reduce Motion or the motion gate keeps them dimmed and still.
Adds the agent-pane.tool-row-shimmer gallery and browser tests covering both animated and static states.