fix: remove 500-message limit to prevent scrollbar jumping in long conversations

[roomote]

Fixes #7063 and #7052

Summary

This PR fixes the scrollbar jumping issue that occurs in long conversations (>500 messages) by removing the array slicing that was causing index shifting.

Problem

When conversations exceeded 500 messages, the chat view would limit the visible messages to the last 500 by slicing the array. This caused:

• The oldest message to be dropped when a new message arrived
• All remaining messages to shift down by one index position
• Virtuoso (the virtual scrolling library) to lose track of the current scroll position
• The viewport to jump to approximately the middle of the conversation

Solution

Implemented Option 1 from the issue analysis: Remove the 500-message limit entirely and let Virtuoso handle virtualization of all messages. Virtuoso is designed to efficiently handle large lists through virtualization, so the memory impact is minimal.

Changes

• Removed the array slicing logic that limited messages to 500 in webview-ui/src/components/chat/ChatView.tsx
• Simplified the visibleMessages useMemo to directly filter modifiedMessages without slicing

Testing

✅ All existing ChatView tests pass
✅ Linting passes
✅ Type checking passes
✅ The fix completely eliminates array index shifting

Impact

This fix ensures that users can follow along with streaming responses in long conversations without the view jumping around, significantly improving the user experience for extended chat sessions.

Related Issues

• Closes 🔍 [TRACKING] Chat Scrollbar Jumping Issue - Investigation & Resolution #7063 (Tracking issue for scrollbar jumping)
• Closes Fix: Scrollbar jumps to middle of conversation due to array index shifting in long chats #7052 (Technical analysis of the root cause)
• Related to Scrollbar does not stay scrolled to the bottom of the RooCode window #6987 (Original report)
• Related to Scrolling in Roo window jumps around #7026 (Another report of the same issue)

---

Important

Removes 500-message limit in ChatView.tsx to fix scrollbar jumping in long conversations, allowing Virtuoso to handle all messages efficiently.

• Behavior:
  • Removes 500-message limit in ChatView.tsx to prevent scrollbar jumping in long conversations.
  • Allows Virtuoso to handle all messages efficiently through virtualization.
• Code Changes:
  • Eliminates array slicing logic in visibleMessages useMemo in ChatView.tsx.
  • Simplifies visibleMessages to filter modifiedMessages without slicing.
• Testing:
  • All existing ChatView tests pass.
  • Linting and type checking pass.
  • Fix eliminates array index shifting.

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[roomote]

Reviewing my own code is like debugging in a mirror - everything looks backwards but the bugs are still mine.

[roomote]

Is this intentional? PR #7053 appears to implement the exact same fix and was created earlier. Should we close one to avoid confusion, or is there a specific reason for having both PRs open?

[roomote]

Consider enhancing this comment to explain why removing the limit fixes the scrollbar jumping:

This would help future developers understand the context better.

[roomote]

While Virtuoso handles virtualization efficiently, have we considered adding telemetry or monitoring for extremely long conversations (thousands of messages)? This could help us track memory usage in production and identify if we need additional optimizations in the future.

Perhaps we could log a metric when conversations exceed certain thresholds (e.g., 1000, 5000 messages)?

[daniel-lxs]

LGTM