fix(console-ui): chat transcript snapping during live status updates

[bradleydwyer]

Fixes #1077.

Original problem

In live mode, frequent status updates rerendered ChatLayout, whose layout effect unconditionally returned the transcript to the latest message. Readers scrolling through a long response were repeatedly snapped back to the bottom.

Diagnostics

The live status stream produced 49 payloads in 12 seconds. Each payload updated the status query, rerendered the chat layout, and ran the unconditional scroll effect. Safari applied the user's scroll normally before the next React render overwrote the position.

Fix

• Track whether the transcript is within 64px of the bottom and only follow new content while that remains true.
• Resume following when the reader returns near the bottom.
• Return to the latest message on conversation switches and explicit Send, Queue, or Retry actions.
• Re-check reader intent inside the deferred animation-frame scroll.
• Add regression coverage for unrelated rerenders, threshold behavior, conversation changes, send/queue/retry flows, and the animation-frame race.

This is a UI-only behavior change with no protocol, storage, or migration impact.

Summary by CodeRabbit

• New Features

  • Chat transcripts now preserve your manual scroll position when you read older messages.
  • Automatic scrolling resumes when you’re near the bottom of the conversation.
  • Sending a message, retrying a response, or switching conversations returns the view to the latest message.

• Bug Fixes

  • Prevented delayed scrolling from overriding upward scrolling.
  • Improved transcript positioning during live updates, retries, and queued messages.

[github-actions]

This pull request is currently a draft. Reviews will not take place until the PR is marked as ready for review.

[coderabbitai]

📝 Walkthrough

Walkthrough

ChatLayout now preserves manual transcript positions unless the reader is near the bottom. ChatPageContent resets bottom-sticking when conversations change or new and retried turns begin, with expanded tests covering these scroll flows.

Changes

Chat transcript scrolling

Layer / File(s)	Summary
Conditional transcript scrolling crates/mesh-llm-ui/src/features/chat/layouts/ChatLayout.tsx	Tracks distance from the transcript bottom, conditionally performs automatic scrolling, resets on stickToBottomKey changes, and wires scroll events from the message list.
Latest-turn reset wiring crates/mesh-llm-ui/src/features/chat/pages/ChatPage.tsx	Adds latestTurnToken, increments it for sends and retries, and passes it with the conversation ID as stickToBottomKey.
Scroll behavior test coverage crates/mesh-llm-ui/src/features/chat/pages/ChatPage.test.tsx	Adds deterministic scroll geometry helpers and tests for manual positions, threshold behavior, queued frames, conversation changes, retries, sends, and queued prompts.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ChatPageContent
  participant ChatLayout
  participant MessageList
  ChatPageContent->>ChatLayout: pass stickToBottomKey
  MessageList->>ChatLayout: report scroll position
  ChatLayout->>MessageList: scroll to latest when enabled

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Suggested reviewers: ndizazzo, i386

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The implementation matches #1077 by tracking bottom proximity, preserving user scroll position, and resetting on conversation changes.
Out of Scope Changes check	✅ Passed	The changes stay within the chat scroll-behavior fix and supporting tests, with no obvious unrelated scope added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main UI fix: preventing chat transcript snapping during live status updates.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ndizazzo]

Thanks for the fix @bradleydwyer!