[teamleaderleo]

Leo (2026-10-20): opening anything on the right side of a chat pane (the Summary from the list icon, the in-chat Browser from the globe, a New Tab column) animated slowly, lagged and drew the panel past the window's right edge. Things that appear should come in from where they belong and leave the way they came.

What changes

Native: right-side panels

• Past the window edge. A Chromium page is a child window. CEFClipShape only handed the fork rounded clips and the strip mask, so a page that a layout spring carried past the screen's edge drew past the window. That is the band beside the Summary in Leo's screenshot. Square-clipping ancestors (the screen, the pane clip) and the window now form a visible region, which is added as a clip when the page reaches past it. At rest it adds nothing.
• Lag. While a pane is on a layout spring (split, close, zoom), PaneHostView holds its content at the larger of its size when the spring started and its size at rest. The content is pinned to the edge nearer its rest and laid out once when the spring lands. The chat keeps its width under an opening panel instead of reflowing on every frame, and the panel lays out at its final size and slides in with its right edge. Terminals already held their grid; now pages do too. Debug toggle motion.pane.holdContent (on).

Webview: directional enter and exit

• ui/presence.ts adds usePresence(shown, edge). It keeps a closing surface mounted until its exit plays and marks it with data-enter and data-presence. ui/popupSurface.css draws the motion with transitions:
  • A reopen during an exit reverses it in place, and a second open changes nothing.
  • Timing comes from the host's --agent-motion-in / -out, so the Motion switches (cmux-next settings: the Motion switches get a home on the Appearance page (Settings base reds) #22628) and ui.animationSpeed govern it.
  • Under Reduce Motion a panel with presence keeps its fade and drops the travel, and an enter-only surface appears at once. Motion off removes it at once.
• Applied to (only the Summary card uses usePresence and plays an exit; the others animate in and close at once):
  • From the right: the Summary card (the inline column travels its own width inside the pane, so the chat lays out once; the popover travels a few points), the session rail, the side preview, Changes and the inspector.
  • From the top: quick open and the find pill.
  • From the left: the narrow pane's sidebar drawer.
  • Rising out of the composer: questions, notices, the PR dock, the agents pill and queued prompts.
  • Popups: they travel a few points out of their trigger by side; the composer's menus rise from it.
• Gallery: agent-pane.summary-motion (open, and open then close).

Popover anchoring and layout stay with the summary-panel lane; this PR only adds motion and the native clip.

Changelog

• Fixed: Panels that open on the right of a chat (Summary, Browser, New Tab) slide in from the right without lag and no longer draw past the window's edge.
• Changed: Panels, cards, bars and drawers in the agent pane enter from the edge they belong to and leave the way they came.

Tests

Red-then-green tests are in the first commit:

• Tests/CmuxNextAppTests/PaneMotionContentHoldTests.swift: a page past the screen's edge is cut there; a shrinking pane keeps its content width until the spring lands; a pane opening on the right lays out at its rest size and rides its right edge.
• webviews/test/presence.test.tsx: enter, exit on transitionend, reopen mid-exit reverses the same node, motion off unmounts at once.

Observed / Not run

• Observed locally: bun test test/presence.test.tsx passes (3 tests). test/summary-card-geometry.test.ts, gallery coverage and manifest tests, and the 44 webview test files about summary, popups, motion, rail, find, bottom stack and inspector all pass. Oxfmt and Oxlint pass on the changed files, and tsc shows no errors in them. The full bun run check fails only on Oxfmt in four settings files this PR does not touch (base).
• Observed on b318d91 (base merge of 2e38ac1): the fleet app compile and link (cmux-ci compile-check --app) passes. CI's cmux-next swift test built the package and tests; its one red test, AgentPaneImageActionsTests.swift:72 followed by an index-out-of-range crash, fails the same way on the unrelated cmux-next: a clicked link's tab takes the focus; closing it gives the focus back #22990 (base). Webview shards: after one rerun, the reds are only the base ones (composer + glyph, gallery coverage, Oxfmt in App.tsx); agent-pane-stream-jitter, thread-minimap-feel and bare-pr-refs passed on the rerun. cmux-next checks: only base reds (Tier routing on CmuxNextHomeEngineTests); "Pushed commits add no violations". Capture: media-tour.
• Not run: CI's own Release compile and Debug scheme compile stayed queued for over three hours (fleet backlog); the fleet app compile above stands in for them. No native before/after recording beyond the media tour.

Agent session: cosmic-gray

🤖 Generated with Claude Code

[teamleaderleo]

Bead cx-ad4l8 created for this PR by the cmux coordinator.

[github-actions]

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

Review f14cb97: 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=pr22795 -f ref=cmux/directional-motion -f platform=macos -f backend_mode=local

Unclear: web / react-apps-check failed: no known signature; failed step: Check webview test shards.

CI failed on b318d91543 (run 39580881321 attempt 1): 2 code, 1 unknown.
macOS jobs did not run: compile and app tests were skipped: Fast static checks skipped.

Job	Verdict	Why
web / react-apps-check (1)	code	a Python test failed
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 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 [1889.22ms]

Not re-run automatically: web / react-apps-check (1), 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: cmux-next checks (god files, concurrency, crash safety, l10n); base red: the same failure on the base 2e38ac1; does not block
red: web / Web status; base red: the same failure on the base 2e38ac1; does not block
red: web / react-apps-check; base red: the same failure on the base 2e38ac1; does not block
red: web / react-apps-check (1); NEW: - [] + [ + "agent-pane.background-hint#claudeAcp: variant names are lower kebab case", + ] - Expected - 1 + Received + 3 at <anonymous> (/tmp/tmprri0aoaw/webvie is not red on the base 2e38ac1; do not merge until green; see lane-rules
red: web / react-apps-check (2); NEW: { "name": "Add", "text": "", - "tooltip": "", + "tooltip": "Add files, screenshots and more", } - Expected - 1 + Received + 1 at <anonymous> (/home/runner/_work is not red on the base 2e38ac1; do not merge until green; see lane-rules

CI fast guards failed on b318d91543 (https://github.com/manaflow-ai/cmux/actions/runs/39580881321). 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 b318d91543 (run): no media. The tour job failed before the tour ran (build or setup); the run log has the output.

[blacksmith-sh]

Found 7 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmp93_eddgs/summary-missing.json (live):/summary-missing.json (live):	View Logs
/tmp/tmpvfrdjq0h/summary-fail.json (live):/summary-fail.json (live):	View Logs
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	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
test_every_source_and_test_directory_is_a_target (main.GraphCoversThePackage.test_e very_source_and_test_directory_is_a_target) (directory='CmuxNextHomeEngineTests')/ test_every_source_and_test_directory_is_a_target (main.GraphCoversThePackage.test_e very_source_and_test_directory_is_a_target) (directory='CmuxNextHomeEngineTests')	View Logs

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

[teamleaderleo]

cmux-next guards / nightly-guards / workflow-guard-tests / release-notary is red on 15 of 18 fresh feat-cmux-next PR heads in the last 2:00:00, so it is most likely a base red, not this PR's. The base-reds lane has it; a base merge picks up the fix once it lands.

[teamleaderleo]

owner: 01a15c78-6428-7081-b456-fe0fcbc491fc

[teamleaderleo]

cmux-next guards / defaults-snapshot is red on 18 of 18 fresh feat-cmux-next PR heads in the last 2:00:00, so it is most likely a base red, not this PR's. The base-reds lane has it; a base merge picks up the fix once it lands.

[teamleaderleo]

Owned by directional-motion-78 on huge-blue · session

[teamleaderleo]

codex-review: SHIP at b318d91

• Reviewed the current diff, focused tests, and affected call paths; no correctness bug found.

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.3959785532701 (e572af1fb9)
• cmux NEXT nightly 1.0.0-nightly.3959940656701 (94e9496e05)