fix: let the composer attachment row follow the macOS scrollers

[teamleaderleo]

Summary

The composer's attachment row (composerAttachments.css) hid its scroller with scrollbar-width: none. check-scrollbars.sh rejects that (SCROLLBARS-FOLLOW-MACOS), so "Scrollbars follow macOS" in the cmux-next checks job is red on every PR based on feat-cmux-next.

This drops the rule. The row keeps overflow-x: auto, so with the default overlay scrollers it looks the same at rest. A scroller appears only while the row scrolls, or always when the user picked "Always" in System Settings, which is what the spec asks for.

Verification

• Red on base 8776bb4: bash scripts/cmux-next/check-scrollbars.sh . prints composerAttachments.css:23: scrollbar-width makes a custom scrollbar and exits 1.
• Green on this head: the same command prints check-scrollbars: ok and exits 0.
• The committed agent-pane bundle (CmuxNextAgentPane/Resources/agent-pane/index.html) inlines this CSS verbatim, so it drops the same line; build-agent-pane-web.sh --check was red on 30e4a79 ("index.html is stale") and is checked again on 67951bb.
• Web tests were not run locally (CSS-only change); hosted CI covers them.

Changelog

none

🤖 Generated with Claude Code

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Summary by cubic

Removes the hidden scrollbar on the composer attachment row so the Scrollbars follow macOS check passes. With default overlay scrollers the row looks the same at rest; a scroller appears only while scrolling, or always when the user chose "Always" in System Settings. The compiled agent-pane bundle drops the same line so the build check stays current.

^{Written for commit 67951bb. Summary will update on new commits.}

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Note

Low Risk
CSS-only tweak to attachment-row scrollbar visibility with no auth, data, or API impact.

Overview
Removes scrollbar-width: none from the composer attachment row styles so horizontal scrolling follows macOS overlay scrollbar behavior instead of hiding the scroller.

The change is applied in composerAttachments.css and the mirrored styles in the macOS agent-pane bundle. overflow-x: auto is unchanged, so the row should look the same at rest with default overlay scrollbars; a scroller shows while scrolling or when the user has “Always” scrollbars in System Settings. This aligns the UI with check-scrollbars.sh (SCROLLBARS-FOLLOW-MACOS) so the cmux-next scrollbars check can pass.

^{Reviewed by Cursor Bugbot for commit 67951bb. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[github-actions]

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

CI failed on 67951bb2f0 (run 37588214371 attempt 1): 1 unknown.
macOS jobs did not run: compile and app tests were skipped: Fast static checks skipped.

Job	Verdict	Why
web / react-apps-check	unknown	no known signature; failed step: Test webviews

Not re-run automatically: web / react-apps-check is not a machine failure.

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.

[lawrencecchen]

Coordinator merge: removes the two scrollbar-width: none lines that broke check-scrollbars (SCROLLBARS-FOLLOW-MACOS) on feat-cmux-next since dd97e43, which cancels the hourly Release compile and blocks nightly-next. The red web/react-apps-check is a base React Compiler report in other acpmux files, unrelated to this two-line CSS deletion.

[github-actions]

Gallery

No state changed

Diff page and renders (the run's gallery-pr artifact)

_{196 unchanged · base 8776bb4 · head 67951bb}