Fix: scroll to bottom on thread load

[urjitc]

Fixes thread loading dropping users at the top of history instead of the latest exchange. <Messages> now calls scrollToIndex(lastIndex, { align: "end" }) on mount when messages exist and we're not streaming, landing the user at the bottom of the thread (typically the most recent assistant response). The existing pin-to-top behavior for new turns remains unchanged.

Summary by CodeRabbit

• Bug Fixes
  • Improved message viewport auto-scrolling behavior when loading or switching between conversation threads for a smoother experience.

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Project	Deployment	Actions	Updated (UTC)
thinkex	Ready	Preview, Comment	Apr 26, 2026 7:06am

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 63dc3d3a-5e54-47a2-bed6-7de466929347

📥 Commits

Reviewing files that changed from the base of the PR and between 83ca5c8 and 0a879b0.

📒 Files selected for processing (2)

• src/components/chat/Messages.tsx
• src/components/chat/ThreadBody.tsx

📝 Walkthrough

Walkthrough

Adds a useLayoutEffect hook to the Messages component that auto-scrolls the virtualized message viewport to the end when a thread loads or switches, using the Virtua list handle to perform the scroll operation via requestAnimationFrame.

Changes

Cohort / File(s)	Summary
Auto-scroll on mount src/components/chat/Messages.tsx	Introduces useLayoutEffect with early-return during streaming or when no messages exist; schedules scroll using requestAnimationFrame and Virtua list handle with empty dependency array to prevent scroll jank.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• Virtualize thread messages with react-virtual #389: Introduces the Virtua virtual list handle that enables the programmatic scroll functionality in this PR.
• Fix chat scroll jitter and reduce viewport slack space #363: Implements complementary "scroll-to-bottom" behavior using similar requestAnimationFrame and viewport reference patterns.

Suggested reviewers

• cubic-dev-ai

Poem

🐰 Hop hop, scroll scroll, the messages now flow,
At thread load we bound to the very last row,
No jank, no jump, just smooth animation,
A virtualized list reaching its destination! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix: scroll to bottom on thread load' directly and clearly summarizes the main change: adding auto-scroll functionality when a thread is loaded.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch capy/scroll-bottom-thread-load

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[greptile-apps]

Greptile Summary

This PR adds a mount-time useLayoutEffect in MessagesImpl that calls scrollToIndex(lastIndex, { align: "end" }) (via requestAnimationFrame) when a thread loads with existing messages and streaming isn't active. A useRef gate ensures the scroll fires exactly once per component mount, and because <Messages> unmounts on every thread switch, the gate resets naturally for each new thread.

Confidence Score: 5/5

Safe to merge — the change is a focused, well-guarded one-shot scroll on mount with no regressions to the existing pin-to-top or streaming flows.

No P0 or P1 issues found. The ref gate, the isStreaming guard, and the rAF deferral are all consistent with the existing patterns in the file. The architectural assumption that unmounts on thread switch is clearly documented in comments and enforced by ChatProvider/ThreadBody.

No files require special attention.

Important Files Changed

Filename	Overview
src/components/chat/Messages.tsx	Adds a one-shot useLayoutEffect that scrolls to the last message index on mount when messages exist and the thread isn't streaming, landing users at the bottom of a loaded thread.

_{Reviews (1): Last reviewed commit: "Scroll to bottom when thread loads so la..." | Re-trigger Greptile}

[cubic-dev-ai]

2 issues found across 1 file

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/components/chat/Messages.tsx">

<violation number="1" location="src/components/chat/Messages.tsx:140">
P2: Custom agent: **Flag AI Slop and Fabricated Changes**

Behavior-changing thread-load scroll fix was added without regression test coverage for the new initial-scroll path.</violation>

<violation number="2" location="src/components/chat/Messages.tsx:146">
P2: This early return leaves the initial bottom-scroll effect armed during active turns, so it can fire right after streaming ends and cause an unexpected jump to bottom.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

0 issues found across 2 files (changes from recent commits).

_{Auto-approved: Isolated UI fix for scroll position on thread load using standard React patterns. Low risk of side effects.}