cmux-next: one model picker, a clickable context ring and an aligned composer footer

[teamleaderleo]

Problem

The agent composer footer ("GPT-6.1-Sol v High v (ring) | mic (send)") had three problems Leo hit in daily use:

• The context ring was a picture with no click, so it never showed what is in the window or offered a way to compact.
• The controls sat on different centers with uneven gaps: 32px chips with 4px gaps, separators with their own margins, and a 16px ring next to a 32px mic.
• Send was a 32px filled circle with an 18px arrow, larger than anything else in the row.

Change

Matches the Codex desktop app composer (left: + then the access chip; right: ring, one model picker, mic, send).

• One model and effort picker. The model chip shows the effort after the model in secondary text, with one chevron. Its menu already has the Reasoning slider, so the separate effort chip is gone. It stays only when an agent offers efforts but no model list. openPicker("Effort") still opens the menu for automation. A default effort adds no text.
• The context ring opens on click. It is a button now. The popover shows the share used, a bar, tokens used of the window ("34K of 200K tokens") and Compact, which sends the agent's /compact when the agent lists that command. A live chat shows the ring from its first frame, and usage fills it in place (stability rule). Before the first usage update it shows 0% with no token counts. The popover is the shared src/ui Popover (Base UI), so Escape and a click outside close it and focus returns to the ring. Nothing depends on hover.
• The permission chip sits next to + again. Plan stays in the + menu.
• One line on an 8px rhythm. Every bar control is 28px tall with 8px gaps and a 10px inset, so the vertical and horizontal insets match in the 48px bar. The separators are gone.
• Send fits the row. It is a 28px circle with a 16px arrow, the same hit size as the mic and the ring.

Builds on #17505 (location row) and #17503 (model labels); #17505's commits are merged in and drop out of the diff once it lands.

ACP usage_update reports only used and window size, so the popover cannot break down what is in context.

Validation

• Red then green: bun test src/agent-session/acpmux/composerPickers.test.tsx (red commit: 25 pass, 6 fail; fix: 31 pass).
• bun test src/agent-session: 1012 pass, 0 fail.
• vp check src/agent-session/acpmux/: format, lint and types clean.
• scripts/cmux-next/build-agent-pane-web.sh --check: bundle current.
• scripts/verify-local.py: the localization parity errors are inherited from feat-cmux-next (none name a key from this PR). No Swift changed; the whole-tree Swift parse cannot run on this Linux host.
• Localization: 4 new agent pane keys (context.title, context.percent, context.tokens, context.compact), labels only, translated into all 21 pane locales and regenerated into generated/strings.json and locales/*.js.
• Fleet before/after captures next to the Codex desktop app reference: cmux-next: one model picker, a clickable context ring and an aligned composer footer #17537 (comment)
• Also formats 7 files feat-cmux-next left unformatted (acpmux/conversation/*, pages/keybindings/model.test.ts), which failed react-apps-check. Formatting only.
• After merging the latest feat-cmux-next: bun test src/agent-session test/ui-rules.test.ts 1054 pass; vp check clean.

Changelog

Fixed the agent composer footer: one model and effort picker, a context ring that opens usage details and Compact on click, every control on one line, and a smaller Send button.

🤖 Generated with Claude Code

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

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Summary by cubic

Redesigns the agent composer footer and location row, and makes every scroller follow the macOS "Show scroll bars" setting instead of forcing overlay or hidden indicators.

• The context ring is now a button; its popover shows window usage and Compact (the agent's /compact) when the agent offers it, and stays at 0% before the first usage update.
• Model and effort share one chip with the effort in secondary text; the separate effort chip remains only when an agent offers efforts but no model list, and openPicker("Effort") still opens the menu for automation.
• Every bar control is 28px tall with 8px gaps and a 10px inset; Send is a 28px circle with a 16px arrow, matching the mic and ring.
• The location row is a quiet row of text menu buttons: a Base UI menu of recent folders using the shared inline location treatment, with the current one checked, path descriptions, Choose folder… and Browse, and the full path as the tooltip. Existing new-chat project selection behavior is kept.
• A press that closes the open context popover does not reopen it.

Scrollbars follow macOS

• SystemScrollers.observe and WebTheme.scrollers propagate the system setting to every webview; the theme sets data-scrollers on <html> and pages re-send it when the setting changes.
• The terminal and native views (site data, certificate details, remote terminal placeholder, Home lists, compose sheet) follow the setting instead of forcing indicator styles.
• Agent pane lists no longer hide their scrollbars, and Monaco, diff rows, and tree scrollbars follow the setting.
• A new check-scrollbars.sh CI gate fails on forced scroller styles, hidden indicators, custom web scrollbars, and overflow: scroll, with a listed exception policy.

^{Written for commit 65fe235. Summary will update on new commits.}

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[github-actions]

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

CI failed on 65fe235b08 (run 37504574040 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.

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Bugbot is paused — on-demand spend limit reached

Bugbot uses usage-based billing for this team and has hit its on-demand spend limit.

A team admin can raise the spend limit in the Cursor dashboard, or wait for the next billing cycle to continue.

[teamleaderleo]

Batch queue: green. Stack next-batch/20261006 at 954248bfe072 (feat-cmux-next 7cf558be8de1 + #17527 #17537 #17542 #17553 #17554 #17559, generated files regenerated) built on the fleet, production: job c8f563681211aa65c6e94453, tag next-batch-f16f40ea (cmux-ci artifact c8f563681211aa65c6e94453). Validated this PR at 7087d7e3c145.

Own check still red: web / react-apps-check, formatting. Run bun run check:fix in webviews/ and push.

Next: land it yourself with gh-merge-green on this receipt.

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Bugbot is paused — on-demand spend limit reached

Bugbot uses usage-based billing for this team and has hit its on-demand spend limit.

A team admin can raise the spend limit in the Cursor dashboard, or wait for the next billing cycle to continue.

[teamleaderleo]

Batch queue: green. Batch stack c03ab5ca52f8 on feat-cmux-next 3892c6ce7b55 with #17520 #17527 #17534 #17537 #17541 #17542 #17551 #17552 #17553. Fleet production build: job d1e25b8a9144e8ef3ef2287e (cmux-ci artifact d1e25b8a9144e8ef3ef2287e (job d1e25b8a9144e8ef3ef2287e, tag nb-local-20261006-160146-1)). heavy tier did not run on this branch (run); your PR's own checks are the tests. Validated this PR at 71989ada83a0.

Next: land it yourself with gh-merge-green on this receipt.

[teamleaderleo]

Batch queue: green. Batch stack 585c7c73df5a on feat-cmux-next b7cd157736d2 with #17534 #17537 #17551 #17552 #17556 #17582 #17583 #17588 #17590. Fleet production build: job 4a08261515853623d652f844 (cmux-ci artifact 4a08261515853623d652f844 (job 4a08261515853623d652f844, tag nb-local-20261006-162817-1)). heavy tier did not run on this branch (run); your PR's own checks are the tests. Validated this PR at e575a6a99879.

Next: land it yourself with gh-merge-green on this receipt.

[teamleaderleo]

Batch queue: green. Batch stack b034a977a4d8 on feat-cmux-next d4056375d08d with #17537 #17597 #17599 #17602 #17604 #17609 #17611 #17613. Fleet production build: job 24360b4ae2a093d871aa1591 (cmux-ci artifact 24360b4ae2a093d871aa1591 (job 24360b4ae2a093d871aa1591, tag nb-local-20261006-180248-1)). heavy tier did not run on this branch (run); your PR's own checks are the tests. Validated this PR at 65fe235b0877.

Next: land it yourself with gh-merge-green on this receipt.

[github-actions]

The feat-cmux-next push run https://github.com/manaflow-ai/cmux/actions/runs/37510605955 at 96f7421 failed: cmux-next generated files, cmux-next swift test.
Those jobs last passed at 9872eec. This pull request is one of 3 merged since: #17599, #17597, #17537.
If the failure is in your change, fix forward on feat-cmux-next. Pull requests run only the tiers their paths reach (docs/ci/cmux-next-tiers.md); label a batch PR full-ci to run them all before merging.

[github-actions]

The feat-cmux-next push run https://github.com/manaflow-ai/cmux/actions/runs/37515600457 at ff267c4 failed: cmux-next swift test.
Those jobs last passed at 3088ebf. This pull request is one of 5 merged since: #17597, #17537, #17621, #17600, #17605.
If the failure is in your change, fix forward on feat-cmux-next. Pull requests run only the tiers their paths reach (docs/ci/cmux-next-tiers.md); label a batch PR full-ci to run them all before merging.