[Bug]: macOS project picker flickers during mouse scrolling; disabling backdrop blur stops it #30759

Summary

On macOS, the entire command-palette project picker and its dimmed backdrop intermittently disappear for a frame while scrolling with a physical mouse. This became noticeable after updating to 0.1.8-nightly.20261104.4165 today; the reporter did not observe it yesterday. It is most noticeable at the beginning of a scroll and becomes less frequent while screen recording.

Related: #23788 and #25552 describe similar older macOS dialog flicker. This report adds a current project-picker reproduction and a live-tested backdrop-blur workaround; it does not establish a different underlying bug.

Environment

• macOS 27.2 (26B123), desktop app.
• T3 Code 0.1.8-nightly.20261104.4165, commit 8b44f42b14c8e273156474a924ccf29680dd7857.
• Electron 44.10.1 / Chromium 152.0.7977.169.
• Physical mouse; mouse model and any scrolling utility were not established.

Steps to reproduce

1. Open the desktop command palette with Cmd+K.
2. Choose New thread in... and have enough projects for the list to scroll.
3. Scroll the project list with a physical mouse, especially the first movement after a pause or opening the picker.
4. Repeat without screen recording if it does not appear immediately.

Expected: the picker and backdrop stay visible throughout scrolling.

Actual: the whole picker, including its text, and backdrop briefly vanish, then return at the expected scroll position. Intermittent; automated wheel input did not reproduce it even in the main desktop window, while the reporter's physical mouse did.

Recordings

Before — reporter's original recording, cropped to the picker (1 second):

Before: project picker flashes during mouse scrolling

After — same installed desktop app with only full-window backdrop blur disabled:

After: project picker scrolling with backdrop blur disabled

The after clip is a roughly 7-second sequence of 40 native desktop captures, encoded as MP4; it is a lower-frequency visual illustration, not proof against single-frame drops. The stronger verification was the reporter repeatedly scrolling with their own mouse without recording during the tests below.

These external evidence links expire approximately 72 hours after upload. Both MP4s are retained locally for reattachment.

Live isolation results

Tested with temporary DevTools CSS overrides in the actual installed desktop window; DevTools was closed before each physical-mouse check.

A MutationObserver probe recorded 28 wheel events during a flickering test with no removal of the existing dialog DOM node. The computed mask was verified as none in the mask-disabled test. Computed styles were also checked for the blur isolation tests.

Potential fix / verified workaround

Remove only the full-window backdrop blur in apps/web/src/index.css:

 @utility dialog-backdrop {
   background: color-mix(in srgb, var(--background) 60%, transparent);
-  -webkit-backdrop-filter: blur(4px);
-  backdrop-filter: blur(4px);

The backdrop tint, dark-mode tint, popup's own glass blur, and scroll-edge fades remain. This is a two-line local source change, not a merged fix or PR. The shared utility also affects other dialogs, alert dialogs, and the Clerk modal backdrop; the visual tradeoff is an unblurred but dimmed page behind them. Web/desktop share this styling; native mobile is unaffected. Other dialogs/platforms have not been behaviorally verified.

Formatting and git diff --check passed; the dev CSS compiled successfully. No UI test was added for this compositor/visual issue.

Regression candidate, not confirmed cause

Electron upgrade #30161 changed 44.10.0 to 44.10.1 on November 3 at 23:49 UTC, between yesterday's nightly and today's. The relevant picker scrolling, dialog styling and backdrop CSS were unchanged in that interval; the 4px backdrop blur itself dates to July 23.

The timing makes the runtime update worth investigating, but no Electron-version A/B test has been performed. The related reports show similar symptoms on older Electron versions, so this could be an existing compositor problem made more visible rather than a new 44.10.1 defect.

Investigated with Codex (gpt-6.1-sol) in T3 Code, with live physical-mouse verification by the reporter.