[Bug]: Working shelf animation overlaps Snoozed and Settled headers#25383

Expanding the bottom-anchored Working shelf briefly draws thread rows over the Snoozed and Settled headers. The labels become superimposed during the transition, even though the layout is correct after it finishes.

Steps to reproduce

1. Enable the Working shelf in the new sidebar design.
2. Have 2 threads in Working, with Snoozed and Settled headers visible below it.
3. Collapse Working, then expand it again.
4. Watch the second Working row while the shelf opens; repeat the toggle if necessary.

Expected behavior

Thread rows and section headers remain separate throughout expanding and collapsing a shelf.

Actual behavior and impact

The newly revealed rows translate through the stationary headers below them. Snoozed and Settled labels overlap thread titles and metadata for part of the 150 ms animation. This is a transient visual defect that makes the sidebar hard to read during a routine toggle, rather than a persistent layout error.

Before: video

https://github.com/user-attachments/assets/ca0d66df-2e2b-4642-83f7-b73cce2027ed

Before: screenshot during the overlap

The video first shows a normal expand/collapse cycle, then holds the opening animation at 60 ms so the overlap can be inspected. The screenshot is from that checkpoint. The 150 ms animation timing and keyframes were not changed. Demo titles and local display states replace private thread data in the evidence.

At the checkpoint, the second Working row spans y=738.23–820.23 px while Snoozed spans y=750–782 px and Settled spans y=783–815 px, so the row intersects both headers.

Environment

• Originally observed in the macOS desktop app; the installed build version was not supplied.
• Reproduced in the Chromium web client on Linux at pingdotgg/t3code commit bfc7177f9f54b0a4b9d3571d30723a51cd4b31bd, 1440 × 900 viewport, dark theme, new design, reduced motion off.
• The desktop app shares this sidebar implementation with web. Provider/model choice is not required to trigger the layout issue.

Searched existing issues for this Working/Snoozed/Settled overlap and did not find a duplicate.

— Brandon Julio Thenaro

Prepared with GPT-6.1-Sol in T3 Code through the Codex harness.