warpbuild-screenshot-repro

Minimum reproduction of a screen-capture issue on WarpBuild's warp-macos-latest-arm64-6x macOS runners.

Symptom

screencapture of an active macOS app (e.g. TextEdit) returns a PNG where:

• The menu bar renders correctly (proves the screencapture pipeline works)
• The entire desktop area below the menu bar is solid black (mean pixel brightness ≈ 5/255)
• The expected window content (e.g. TextEdit's "Untitled" document with toolbar/ruler) is not visible

This blocks any workflow that needs visual verification of macOS apps in CI: XCUITest screenshot diffs, dogfood screenshots after build, screen recording for visual regression, etc.

Repro

.github/workflows/repro.yml runs two jobs side-by-side:

1. warpbuild — runs-on: warp-macos-latest-arm64-6x
2. github-hosted-control — runs-on: macos-15 (GitHub-hosted)

Both:

open -a TextEdit
sleep 4
screencapture -x desktop.png

Then measure mean pixel brightness for the full image and the body region (excluding menu bar).

Expected: WarpBuild body brightness ≈ 5 (black), GitHub control body brightness > 100 (real desktop with TextEdit window visible).

Trigger

Push to main or run manually:

gh workflow run repro.yml --repo manaflow-ai/warpbuild-screenshot-repro

Then download the screenshots artifact to compare.

Suspected root cause

Apple's Virtualization.framework does not pass the host GPU through to macOS guests, so Metal/CoreAnimation has no real compositor target. Window backing stores never get rasterized.

Reference: cirruslabs/tart#1032.

This is consistent with what we observe on:

Provider	Result
WarpBuild warp-macos-latest-arm64-6x (M4 Pro Virtual)	❌ black
Depot depot-macos-latest (M2 Pro Virtual)	❌ black
GitHub macos-15 and macos-15-xlarge	✅ renders
Self-hosted physical Mac mini (M4)	✅ renders

GUI session itself is fine on WarpBuild (launchctl print gui/$(id -u) shows type=login session=Aqua creator=loginwindow, WindowServer is running). The problem is GPU-side, not session-side.

What we'd love to know

Is GPU-accelerated macOS on WarpBuild's roadmap? The M4 Pro hardware is great otherwise.