ChatView: smoother stick-to-bottom during streaming

[hannesrudolph]

Fixes issues where sometimes the session would lose its stickyness to the bottom of the window during streaming events.

BEFORE

Sticky.-.Old.mp4

AFTER

Sticky.-.New.mp4

Summary

• Smoother, reliable stick-to-bottom during token streaming
• Use Virtuoso followOutput="smooth" + sticky follow mode
• Engage sticky on “scroll to bottom”, auto-disengage on user up-scroll or expanding rows
• All chat tests pass

Key changes

• ChatView: enable followOutput and manage sticky pin: webview-ui/src/components/chat/ChatView.tsx
• Guard textarea and row-height scrolls using isAtBottom

Tests

• webview-ui chat specs: 99/99 passing

Rationale

• Removes after-render debounce jumps and reduces complexity
• Lets Virtuoso own bottom-follow; tiny sticky follow ensures robust pin under fast streams

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Important

Enhances stick-to-bottom behavior in ChatView.tsx during streaming by using stickyFollowRef and isAtBottom for smoother scrolling and accurate UI updates.

• Behavior:
  • Improved stick-to-bottom behavior during streaming in ChatView.tsx using stickyFollowRef and isAtBottom.
  • Engages sticky follow on "scroll to bottom" and disengages on user up-scroll or row expansion.
  • Uses Virtuoso with followOutput="smooth" for smoother scrolling.
• State Management:
  • Replaces disableAutoScrollRef with stickyFollowRef for managing sticky follow state.
  • Updates isAtBottom state to track scroll position and control UI elements.
• UI Updates:
  • Shows/hides scroll-to-bottom button based on isAtBottom state.
  • Adjusts button visibility logic in the chat interface to reflect scroll position changes.

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[roomote]

Reviewed commit 9df6649. No new issues found.

Previous Reviews

• f858676: Review #1
• 27cb8ae: Review #2

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[Copilot]

Pull Request Overview

This PR refactors the auto-scroll behavior in the chat view by replacing the disableAutoScrollRef pattern with a more intuitive "sticky follow" approach that works in conjunction with Virtuoso's built-in followOutput feature.

Key changes:

• Renamed disableAutoScrollRef to stickyFollowRef with inverted logic (true = follow enabled, false = follow disabled)
• Added followOutput="smooth" to the Virtuoso component to leverage built-in scroll following
• Removed the custom auto-scroll effect that triggered on message length changes
• Simplified scroll behavior logic in atBottomStateChange and wheel event handlers

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