[teamleaderleo]

Summary

Leo, 2026-10-20: typing a newline in the composer (Shift-Return, or a wrap) makes the transcript's scrollbar jump. Growing the composer must never move the transcript's scroll position, and a view following the latest row stays at the end.

• agent-pane-scrollbar-full-height.test.ts, sampled after every painted frame while typing five lines with Shift-Return, deleting three, then clearing the draft:
  • "a composer that grows leaves a reader scrolled up where they were on every frame": a reader scrolled up is never moved (no frame's scrollTop differs by more than half a pixel).
  • "a composer that grows and shrinks keeps a followed view at its end on every frame": the latest row stays visible above the composer's card on every frame (no row under the card, never past the end), and it holds the same spot over the card throughout, so the view neither lags a frame nor overshoots.
  • The existing case "a composer that grows keeps the followed end above it on every frame".

Changelog

none

Testing

Command: cd webviews && CMUX_BROWSER_TESTS=1 bun test test/agent-pane-scrollbar-full-height.test.ts (real Chromium).

Observed / Not run

• CI (Chromium) on 3604d2a and 030cac5: PASS test/agent-pane-scrollbar-full-height.test.ts. The guards pass on the current code, so the same-frame lockstep needs no fix for these cases. This PR adds guards only.
• Other web / react-apps-check reds on this head are in files this PR does not touch: + is its glyph, named Add with no tooltip (also red on base run 39386215666) and timeouts in composer-location-strip, composer-draft-wrap and composer-type-scale.
• Not run: WebKit (the test is Chromium-only), and a line made by wrapping instead of Shift-Return.

Agent session: cosmic-gray

🤖 Generated with Claude Code

[teamleaderleo]

Owned by composer-scroll on cosmic-gray · session

[github-actions]

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

Review 2e6856a: 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=pr23186 -f ref=cmux/composer-grow-scroll -f platform=macos -f backend_mode=local

Unclear: web / react-apps-check (4) failed: no known signature; failed step: Test webviews.

CI failed on 2e6856abd9 (run 39574025151 attempt 1): 2 code, 2 unknown.

Job	Verdict	Why
web / react-apps-check (1)	code	a Python test failed
web / react-apps-check (4)	unknown	no known signature; failed step: Test webviews
web / react-apps-check (2)	code	a web test failed
web / react-apps-check	unknown	no known signature; failed step: Check webview test shards

Failures:

• seen on other PRs gallery-coverage.test.ts gallery coverage > the entries are valid: failed (job)
• seen on other PRs agent-pane-math.test.tsx each delimiter typesets once math appears: failed (job)
• seen on other PRs composer-claude-split.test.ts chromium: + is its glyph, named Add with no tooltip: failed (job)
• seen on other PRs composer-claude-split.test.ts webkit: + is its glyph, named Add with no tooltip: failed (job)

Matched log lines

web / react-apps-check (1): FAIL: test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format (__main__.ScopedChecksTests.test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format)
web / react-apps-check (2): (fail) chromium: + is its glyph, named Add with no tooltip [1934.07ms]

Not re-run automatically: web / react-apps-check (1), web / react-apps-check (4), web / react-apps-check (2), web / react-apps-check are not machine failures.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's; yours means the failing file is one this PR changes, also red on main that main's latest full suite fails the same way, seen on other PRs that it failed on another pull request's run lately.

red: web / Web status; NEW: green on the base 0d59bfd; do not merge until green; see lane-rules
red: web / react-apps-check; no finished base run on 0d59bfd to compare; do not merge until green; see lane-rules
red: web / react-apps-check (1); no finished base run on 0d59bfd to compare; do not merge until green; see lane-rules
red: web / react-apps-check (2); no finished base run on 0d59bfd to compare; do not merge until green; see lane-rules
red: web / react-apps-check (4); no finished base run on 0d59bfd to compare; do not merge until green; see lane-rules

CI fast guards failed on 2e6856abd9 (https://github.com/manaflow-ai/cmux/actions/runs/39574025151). It does not block the merge; a red guard merged into main breaks it for every open PR.
The log named no failed step; see the run.

Agents: python3 scripts/ci/guard_attribution.py fix applies the mechanical fixes locally.

Tour of 2e6856abd9 (run): no media. The tour did not run: only webview code changed (1 path(s)), which the gallery advisory run checks in Linux Chromium on the pull request (its artifact holds any captures); add the media-tour-mac label to tour it on a Mac.

[teamleaderleo]

Bead cx-cfkhb created for this PR by the cmux coordinator.

[blacksmith-sh]

Found 5 test failures on Blacksmith runners:

Failures

Test	View Logs
test/agent-pane-math.test.tsx/agent-pane-math.test.tsx	View Logs
test/agent-pane-math.test.tsx/agent-pane-math.test.tsx	View Logs
test/composer-claude-split.test.ts/composer-claude-split.test	View Logs
test/composer-claude-split.test.ts/composer-claude-split.test	View Logs
test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format (main.ScopedChecks Tests.test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format)/ test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format (main.ScopedChecks Tests.test_coverage_base_gap_warns_on_a_pr_changing_the_gallery_format)	View Logs

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.3958372135301 (bc661dae0e)