[teamleaderleo]

A tool call expanded at the transcript end now keeps that scroll extent when it collapses. Its header stays in place, and scrolling up and back—including scrolling before the collapse is first measured—keeps the blank room. New content can consume the room; Send, Jump to latest and switching chats reset it.

The assigned request, forwarded from Leo: “the bottom space added when a tool call expands must stay after it collapses, and after scrolling up.” Leo also clarified: “i literally said dont fold the steer”.

This builds on the landed #29686 expansion animation and #29740 steer/footer behavior. A browser regression verifies that the personal steer and assistant reply immediately before it stay visible across Worked-for toggles. The PR changes only scroll-room retention and its browser tests.

Design reference: leo-workspace/design/chat-transcript.md, Tool expansion at the bottom, updated for this behavior. Expansion keeps base's single compositor move; tool collapse retains the expanded end. No new timers or observers. Risk is scroll anchoring during a collapse; browser coverage measures extent, header movement and immediate reader input.

Validation:

• 52 passed, 0 failed in fleet run 41252283774 at 6b9cb38aec80f09f23f685a0999e1fe1ca0890e4: fold-anchor browser tests, popover animation audit, steer continuity and turn/footer tests.
• Base integration at a83f3e8b482fc03abc06cd13157e6f53e867ef66 leaves the retention implementation and tests unchanged. Independent exact-head review passed; all eight automated webview base-check verdicts passed at the final head.
• git diff --check passes.

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 a83f3e8: 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=pr29703 -f ref=lane/transcript-bottom-space-keep -f platform=macos -f backend_mode=local

Gallery before/after for a83f3e8: 16 states rendered, 0 images differ, 1100 more touched states not rendered. Images are in the run's artifact, not on this public PR; the independent review of this head reads them on its own, so the PR needs no hand-made screenshots of these states.

gh run download 41253650297 -R manaflow-ai/cmux -n gallery-advisory-29703-a83f3e8b482fc03abc06cd13157e6f53e867ef66 (then read gallery-review.json)

States

State	Theme	Status	Diff	Picked by
agent-pane.chat-width/standard	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/standard	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.chat-width/wide	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/wide	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.chat-width/wide-blocks	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.chat-width/wide-blocks	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/short-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/short-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/wide-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/wide-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-edge/no-edge	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-edge/no-edge	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-floats/scrolled-to-end	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-floats/scrolled-to-end	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.composer-floats/composer-grown	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.composer-floats/composer-grown	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/shipped	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/shipped	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/two-thirds	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/two-thirds	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/half-tucked	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/half-tucked	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/before	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.continuation-spacing/before	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.copy-controls/output	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.copy-controls/output	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.docked-chat/new-chat	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.docked-chat/new-chat	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.docked-chat/after-turn	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.docked-chat/after-turn	Apple System Colors	unchanged	0%	own App.tsx
agent-pane.docked-chat/working	Apple System Colors Light	unchanged	0%	own App.tsx
agent-pane.docked-chat/working	Apple System Colors	unchanged	0%	own App.tsx

_{Pick other states with a Gallery: entry.id, entry.id/variant line in the PR body.}

Passes: CI passes on a83f3e8b48.

CI passes on a83f3e8b48 (run 41253650532 attempt 1).

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.

web and size checks: green

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4130052256501 (28aa638015)

[teamleaderleo]

Review (subagent): SHIP at c322f89

[teamleaderleo]

Review (subagent): SHIP at c322f89

[teamleaderleo]

Review (subagent): SHIP at 4ee8970

[teamleaderleo]

Review (subagent): SHIP at 4ee8970

[cursor]

Bugbot needs on-demand usage enabled

Bugbot uses usage-based billing for this team and requires on-demand usage to be enabled.

A team admin can enable on-demand usage in the Cursor dashboard.

[teamleaderleo]

Review (subagent): SHIP at 6bc2412

[teamleaderleo]

Review (subagent): SHIP at 23f20a4

[teamleaderleo]

Review (subagent): SHIP at fd1fe34

[teamleaderleo]

Review (subagent): SHIP at ea3db30. Independently inspected the diff and carried steer/footer changes. The observed-shrink guard prevents immediate reader scrolling from releasing bottom room before collapse measurement; collapse retains the clicked line and extent, and base expansion behavior remains intact. No blocking findings. Fleet validation pending.

[teamleaderleo]

Review (subagent): SHIP at 6b9cb38. Verified the final delta restores the incoming report continuation marker; personal-steer retention explicitly excludes incoming reports. Prior full review found no blocking issues in retained bottom room, immediate-scroll handling, base expansion motion, and carried steer/footer behavior. Fleet at the preceding head passed both new bottom-room cases and the personal-steer browser case; the corrected report fixture is being rerun.

[teamleaderleo]

Review (subagent): SHIP at a83f3e8. Independently inspected the full two-file diff and base integration. The retention implementation and regression tests are unchanged; incoming App changes are outside VirtualTranscript. No blocking findings. diff --check passed; final automated webview verdicts pending.

[blacksmith-sh]

Found 4 test failures on Blacksmith runners:

Failures

Test	View Logs
main.DeveloperIdAppTests.test_download_prints_the_active_profile_only/ test_download_prints_the_active_profile_only	View Logs
stubs: /System/Library/Frameworks/Security.framework/Versions/A/Security has no stub/ Security has no stub	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_CFRetain']/ CoreFoundation, missing 1: ['_CFRetain']	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_log2']/ CoreFoundation, missing 1: ['_log2']	View Logs

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