fix(mothership): stop-button transitions freeze in place

[TheodoreSpeaks]

Summary

• Hitting stop no longer settle-scrolls: a user stop suppresses the post-stream chase (shouldFollowSettle), so the transcript freezes where it is
• "Stopped by user" now swaps into the thinking shimmer's slot in the same render — stopping mid-"Thinking…" reads as an in-place replacement instead of a collapse/mount shuffle
• Fixed a 1px/frame upward creep when the sizer floor is load-bearing (fractional min-height rounded scrollHeight above the scrolled-to extent; now Math.floored)

Type of Change

• Bug fix

Testing

Tested manually on a local dev server (stop mid-thinking, credential-request reply); vitest 110/110 in the touched tree; lint + strict boundary validation + typecheck clean

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Jul 22, 2026 7:24pm

[cursor]

PR Summary

Medium Risk
Touches intricate pinned-scroll, virtualizer sizing, and end-of-turn layout in the primary workspace chat; regressions would show as scroll jumps or stuck follow, but no auth or data-path changes.

Overview
Improves stop and end-of-turn behavior in mothership chat so the transcript does not jump or creep when generation ends or the user hits stop.

Message tail layout: "Stopped by user" and message actions now render in the same fixed-height tail region as the thinking shimmer (TAIL_REGION_CLASSES), so mid-stop replaces the shimmer in place instead of collapsing and remounting elsewhere. When a stopped block follows trailing text, reveal/scroll hooks stay on the text segment until the reveal finishes, not on the stopped marker.

Scroll / auto-follow: Chat scroll containers disable overflow anchor. Auto-scroll follows sizer ResizeObserver growth (replacing subtree mutation + CSS animation follow), extends post-teardown idle chase (~800ms) for late-mounted stop UI, and cancels overlapping settle when a new stream starts. The virtualizer sizer min-height floor uses Math.floor, a 1px dead-band, and an eased drain at SMOOTH_CHASE_RATE instead of clearing all phantom height at once. createSmoothBottomChase compares scroll-top vs content-bottom moves so floor drains are not mistaken for user scroll-up.

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[greptile-apps]

Greptile Summary

This PR fixes transcript movement around user-stopped chat turns. The main changes are:

• Replaces the thinking shimmer with the stopped marker in place.
• Keeps reveal tracking active for text immediately before a stopped marker.
• Adds a short, cancellable settle chase after streaming ends.
• Drains the virtualized sizer floor gradually and limits fractional-pixel feedback.
• Disables native scroll anchoring in both chat layouts.

Confidence Score: 5/5

This looks safe to merge.

• The latest changes preserve reveal tracking through stopped turns.
• Settle listeners and animation handles are cleaned up on resend and unmount.
• The floor drain handles visible debt without restoring the earlier abrupt clamp.
• No blocking issue was found in the changed code.

Important Files Changed

Filename	Overview
apps/sim/app/workspace/[workspaceId]/home/components/message-content/message-content.tsx	Moves the stopped marker into the tail region and keeps reveal callbacks attached to trailing text.
apps/sim/app/workspace/[workspaceId]/home/components/mothership-chat/mothership-chat.tsx	Adds scroll-anchor control and a guarded, debt-aware sizer-floor drain.
apps/sim/hooks/use-auto-scroll.ts	Uses sizer resize observation and retains cleanup for the post-stream settle window.
apps/sim/lib/core/utils/smooth-bottom-chase.ts	Separates user upward scrolling from movement caused by content shrink.

_{Reviews (11): Last reviewed commit: "fix(mothership): debt-aware drain fast-p..." | Re-trigger Greptile}

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