[Bug]: Thread info panel has a rectangular shadow behind its rounded card

[PixPMusic]

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web (shared desktop UI)

Steps to reproduce

1. Set Appearance to Iris dark, contrast to 200%, and glass opacity to 100%.
2. Open the thread info panel from the upper-right toolbar, in a window narrow enough to use its floating popover presentation.
3. Inspect the shadow around the panel, especially its left and bottom edges. This is visible on a new thread and an existing thread with Lineage entries.

Expected behavior

No rectangular shadow or frame should appear behind the rounded card. Any shadow should follow the card shape and fade smoothly into the background.

Actual behavior

A rectangular shadow/frame with square corners appears behind the rounded card. Its outer edges have an abrupt cutoff. The attached examples show this with short and tall panels.

Impact

Cosmetic issue

Version or commit

Reported on October 2, 2026. Exact installed version was not recorded. Investigation base: main @ db51460.

Environment

macOS desktop; Iris dark theme, 200% contrast, fully opaque glass.

Screenshots

Workaround

No workaround confirmed.

Additional theme evidence

Matched before/after comparisons in PR #15069 cover Iris light and the default T3 Code Light/Dark themes at the same 200% contrast and 100% glass opacity. The wrapper is already shadowless in both light themes. T3 Code Dark has the same extra rectangular shadow as Iris dark, but it is less visible against the nearly black background.