[teamleaderleo]

Summary

webviews/test/transcript-upward-anchor.test.ts "received card folds preserve painted row-box adjacency while streaming" is red on every cmux-next web push run on feat-cmux-next (expect(result.compared).toBe(result.frames): 130 or 132 of 136), for example run 41581500665 at 53921ff, job "web / react-apps-check (8)".

Cause

The test scrolls the received card (gap-incoming, in the fixture's last turns) to the top of the view. Its content below is shorter than the view, so that lands at the transcript's physical end. Since #32644, opening a line at the very bottom deliberately pushes the text above it up (Leo, 2026-11-02: "YOU EXPAND UP WHILE YOUR SCCROLL IS AT THE VERY BOTTOM AKA YOU PUSH THE TEXT UP VISUALLY INSTEAD OF EXPANDING DOWN LIKE USUAL / JUST THAT CASE"), and #32943 holds the rows under the opened line with a clip on what rises. In the trace's transcript-fold-stream: line that shows up as:

• the open at frame 4: scrollTop 745119 to 746283, and the card's top goes from 15.75 to -1148 (drift -1164, missing anchors), with two frames where the clipped card's box overlaps the held rows by 1148px (getBoundingClientRect ignores the clip);
• the close at frame 32 of a toggle now 1148px above the view: three frames with no row in the view until the view comes back to the end.

That is the push-up behaviour #32644 asked for, seen by an oracle that expects the line to keep its place. #32644 already moved the other keep-place tests off the bottom (agent-pane-fold-keeps-place.test.ts, received-message-fold-browser.test.ts); this trace was missed.

Fix

Test only. Before the trace, put the view 48px up from the end, the same way agent-pane-fold-keeps-place.test.ts does, and assert it is more than 8px from the end. The trace again checks what it was written for (#27365): a received card that folds in place while the last reply streams, with no drift, gaps, overlaps or blank frames. The very-bottom push-up keeps its own coverage in transcript-expand-at-bottom.test.ts.

Base-red-job: web / react-apps-check

Changelog

none

Observed / Not run

• Red on base: the CI log of job 125737298566 (above), Expected: 136, Received: 130; runs 41580824945 and 41580790250 the same way.
• Green at head 668ba6c, three times: cmux-ci test --setup webviews -- bash scripts/ci/run-webviews-tests.sh test/transcript-upward-anchor.test.ts (run 41590121087, PASS), then bun test test/transcript-upward-anchor.test.ts twice in one step (run 41591800362): 7 pass, 0 fail each time, the fold-stream test included.
• Not run: the full webviews suite (CI runs it on this PR).

Agent session: agent session

🤖 Generated with Claude Code

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review eece95f: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr33135 -f ref=lane/web-base-red-upward-anchor -f platform=macos -f backend_mode=local

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4161217392901 (1a7e2c1865)
• cmux NEXT nightly 1.0.0-nightly.4162023985101 (c8f5046a98)

[teamleaderleo]

Review (codex gpt-6-astra high, sweep, via the review router; full diff from merge base e8b1b7d to this head): SHIP at 668ba6c

No P1/P2 findings.

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[teamleaderleo]

Review (subagent opus-5.5 medium): SHIP at eece95f

Visual verdict: unchanged by this diff (test only).

Checked the cause: the collapsed received card sits 8 short rows from the end, so scrollIntoView({block:"start"}) sometimes clamps to the physical end, and the frame-4 open then takes beginBottomStackFold (#32644, within the 4px deadband), pushing the visible rows out (null anchors, short compared). Starting at min(scrollTop, end - 48) drops follow (onScroll moved up, not at latest), the stream step barely changes height, the later folds keep place, the card stays in view for all 4 clicks, and every strict assertion is unchanged plus a loud fromEnd > 8 guard. cmuxPaintFrame comes from installPaintedFrames.

Green 3/3 in one step at this head, fmt clean: https://github.com/manaflow-ai/cmux/actions/runs/41601762114

Follow-ups:

• [follow-up] page.evaluate(() => document.fonts.ready) returns a FontFaceSet across the boundary; harmless, .then(() => undefined) reads clearer.
• [follow-up] Recheck fromEnd after the first stream frame to make the "reply keeps about its height" assumption explicit.