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[Bug]: Opening a remote thread renders at the top, then animates a scroll all the way to the bottom #14224
Description
Activity
Root cause, from reading the code on
mainat 8f75697. I haven't reproduced it in a live client.- While a thread is working, the web timeline scrolls with an animated
maintainScrollAtEnd(apps/web/src/components/chat/MessagesTimeline.tsx~L1357-1367). That was added in feat(server): show finished paragraphs and code blocks while the response streams #11062 so streamed paragraphs glide in. The only guard is a two-frame "settling" window after a thread switch (~L592-600, cleared at ~L634-646). - For a running thread,
isWorkingcomes from the thread summary, which arrives before the messages (ChatView.tsx~L3531). So the list pins to the end while it holds only the thinking row. - The messages arrive later as one data change with
animated: true. The transcript paints at scrollTop ≈ 0 and then glides through every row to the bottom. - It shows up over a tunnel because local responses usually land inside the two-frame window, which uses the instant scroll. Running threads are also never written to the local cache (
packages/client-runtime/src/state/threads.ts~L109-121), so every open fetches from scratch. That's why it happens each time I check on a long run. - Idle threads aren't affected. Mobile isn't either: its follow scroll is never animated, and fix(mobile): running threads open at the latest message #13530 fixed the mobile version of this. fix(web): return to the saved scroll position after switching threads #14212, fix(web): reopen a thread that was following its stream at the end #14916 and fix(web): programmatic scrolls jump instead of glide when Reduce Motion is on #16014 don't touch this path.
Possible fix (~10-15 lines): keep the instant variant until the thread detail finishes syncing (
threadSyncPhase === null), and restart the settling window when that changes. Streaming after load keeps its glide. I'm happy to send a PR with a recording if this direction works.Interim workaround: turning on macOS Reduce Motion makes it snap instead.
- While a thread is working, the web timeline scrolls with an animated
Before submitting
Related: #5903, #14051, and #13601 are about threads settling in the wrong place. In this case the thread does reach the bottom. The problem is how it gets there: it renders at the top and then plays a long animated scroll through the whole transcript.
Area
apps/web
Steps to reproduce
Expected behavior
The thread opens already pinned to the latest message, with no visible scrolling. I check on long agent runs every ~15 minutes and only want to see the bottom.
Actual behavior
The thread first renders at the top of the transcript. Then it plays a smooth-scroll animation all the way down to the latest message. In a long thread, with lots of tool calls, the animation is slow and distracting, and it plays every time I open the thread to check on it.
Impact
Minor bug or occasional failure
Version or commit
v0.0.42 (desktop client and server)
Environment
Client: T3 Code (Alpha) desktop app 0.0.42 on macOS 26.2 (25C56), Apple M5, Electron 44.1 / Chrome 152. Server:
t3 servev0.0.42 on Linux (kernel 7.0.0), reached through the built-in cloudflared tunnel.Logs or stack traces
No response
Screenshots, recordings, or supporting files
No response
Workaround
None. Waiting for the animation to finish, or pressing End, gets to the bottom.