[Bug]: Picking up a sidebar thread to reorder it starts the drag far below the pointer #27586

Before submitting

• I searched existing issues and did not find a duplicate. Nearby but different: [Bug]: 0.1.5 cannot drag a thread to the top of the list, and renaming a thread title does not work #27195 (drag does not start at all on 0.1.5), [Bug]: Pen taps on sidebar rows start a drag and lose their click #26548 (pen taps start a drag), [Bug]: Boring sidebar: threads can no longer be dragged onto the composer #26676 (boring sidebar cannot drag onto the composer).
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Open T3 Code (Beta) 0.1.5 on macOS with the default (non-boring, non-legacy) sidebar and Working section turned off.
2. Have several threads in the Active list.
3. Press on a thread row and start dragging it up or down to reorder it.
4. This happens even with the sidebar scrolled all the way to the top, so it does not depend on the list's scroll offset.

Expected behavior

The lifted row stays under the pointer at the spot where it was picked up, and moves with the pointer from there.

Actual behavior

As soon as the drag starts, the lifted row (and the insertion gap) jumps a long way down the list, to roughly the middle of the Active list, well below the pointer. The drag then continues from that position. It happens with the sidebar scrolled to the very top as well. Reordering to a nearby spot means dragging all the way back up from the wrong place.

This makes manual ordering painful, and with Working turned off manual ordering is the only way to keep recent threads near the top (the Active list ignores "Last user message" there, see #21639).

Impact

Major degradation or frequent failure

Version or commit

T3 Code (Beta) 0.1.5 (6d450a4)

Environment

macOS 27.0.1 (26A434), desktop app. Sidebar settings: Working section off, boring sidebar off, legacy sidebar off, project grouping "repository".

Workaround

None found.