[teamleaderleo]

Summary

Narrow the WebKit follow repair to the current feat-cmux-next base. Streaming bottom-following now uses a 2 px resting deadband and only writes a meaningful correction, preserving the follow trace across a second composer send without carrying the unrelated sidebar/motion changes from #21331.

Validation

• bun test test/transcript-follow.test.ts (browser lane skipped outside CI/Freestyle)
• CMUX_BROWSER_TESTS=1 bun test test/transcript-follow.test.ts (local DOM timeout while starting the Vite browser lane; hosted WebKit remains required)
• bun run typecheck (no type errors in 1482 files)
• git diff --check

The existing transcript-follow browser test already asserts the <=2px follow tolerance. Hosted WebKit/Chromium validation is required on this exact head before merge.

---

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Summary by cubic

Sets bottom-following to a 2px resting deadband in the agent transcript, so streaming replies no longer write fractional scroll offsets and twitch the thumb.

• The new settleFollowBottom helper only corrects when displacement exceeds the deadband, which also preserves the follow trace across a second composer send.
• Applies only the follow repair onto the current feat-cmux-next base; unrelated sidebar and motion changes are not carried over.

^{Written for commit d95c7ac. Summary will update on new commits.}

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[teamleaderleo]

Visual preview of d95c7ac: in the maintainers' private review feed.

[teamleaderleo]

Bead cx-20rww created for this PR by the cmux coordinator.

[github-actions]

Gallery

Review in feed

24 states changed: agent-pane.chat-width/wide, agent-pane.chat-width/wide-blocks, agent-pane.transcript/math-delimiters, agent-pane.transcript/github-references, agent-pane.replay/playing, ... · 1 play check failed

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

State	Before · after
agent-pane.chat-width/wide (Apple System Colors, chromium)
agent-pane.chat-width/wide-blocks (Apple System Colors, chromium)
agent-pane.chat-width/wide-blocks (Apple System Colors Light, webkit)
agent-pane.transcript/math-delimiters (Apple System Colors Light, chromium)
agent-pane.transcript/math-delimiters (Apple System Colors, chromium)
agent-pane.chat-width/wide (Apple System Colors Light, chromium)

18 more on the diff page.

Live preview (follows this branch; start it with scripts/gallery-live.sh up <branch> from an hq checkout):

• agent-pane.chat-width/wide: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.chat-width#/agent-pane.chat-width/wide
• agent-pane.chat-width/wide-blocks: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.chat-width#/agent-pane.chat-width/wide-blocks
• agent-pane.transcript/math-delimiters: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.transcript#/agent-pane.transcript/math-delimiters
• agent-pane.transcript/github-references: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.transcript#/agent-pane.transcript/github-references
• agent-pane.replay/playing: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.replay#/agent-pane.replay/playing
• agent-pane.transcript/keyboard-focus: /wt/codex-cx9vqcn-follow-fix/?entry=agent-pane.transcript#/agent-pane.transcript/keyboard-focus
• 7 more on the diff page

Play checks failed (0 px anchor movement, 0 layout shift, no frame over 33 ms unless the entry gives a reason):

• agent-pane.thread-minimap/long-chat (Apple System Colors Light, webkit): play: waitFor did not hold within 5000 ms
• agent-pane.thread-minimap/long-chat (Apple System Colors, webkit): play: waitFor did not hold within 5000 ms

69 nondeterministic states differed from a second render of the same head (a clock or fixture leak) and are not counted as changes.

_{467 unchanged · base 81f1c75 · head d95c7ac}

[teamleaderleo]

Superseded by #21363, which carries the current-base follow fix plus the cx-ncc.58 composer-slot regression and focused tests.