fix(browser): restore a working rasterizer for screen-share capture

[Lazare-42]

Problem

Teams recordings turn into row-shifted garbage the moment someone screen-shares. Confirmed on prod bot cdb011f5-9530-4a3c-81af-5ef42baaaafa (2026-07-09, customer-reported): clean for the first 3 min, then 46 minutes of unusable video — and zero errors logged. Corruption is present in raw_video.mp4, i.e. at capture, so ffmpeg/branding is not involved. The Teams DOM overlay stays crisp, so x11grab is fine — Chromium is painting the video surfaces as garbage.

Reproduced live on prod today with a fresh bot + screen share.

Cause

f531646 (Jul 2) moved Teams from plain Chrome to CloakBrowser, carrying over these flags:

--disable-gpu --disable-software-rasterizer --disable-gpu-compositing

CloakBrowser launches through Playwright with ignoreDefaultArgs = ["--enable-automation", "--enable-unsafe-swiftshader"] (its config.js), so it drops the SwiftShader flag Playwright normally passes, and adds --ignore-gpu-blocklist in headed mode. Result: no hardware GPU, no SwiftShader, no GPU compositing — but the blocklist ignored. Nothing is left that can raster a large surface. Small camera tiles still paint; a full-size share track does not.

The pre-Jul-2 Chrome path passed no GPU flags and kept --enable-unsafe-swiftshader, which is why this never happened before. Meet has run this same broken combo since Jun 2 — its screen-shares are likely affected too, just unreported.

Fix

BROWSER_GPU_MODE env var selects the flag set (browser/browser.ts):

mode	flags
swiftshader (default)	--disable-gpu --use-gl=angle --use-angle=swiftshader
none	(none — pre-Jul-2 plain-Chrome behaviour)
legacy	the broken combo, kept to reproduce on demand

Env-selectable so preprod can bisect the three variants without rebuilding the image.

Note: --enable-unsafe-swiftshader is deliberately not passed — Playwright applies ignoreDefaultArgs as a filter over the whole arg list, user args included (coreBundle.js:38322), so it would just be stripped again. It only gates WebGL; ANGLE-SwiftShader raster/compositing works without it.

Test plan

• Preprod Teams bot + screen share on swiftshader → clean capture
• If still corrupt, flip BROWSER_GPU_MODE=none (no rebuild) → clean capture
• Confirm Meet join/record unaffected (Meet keeps CloakBrowser)
• Then promote to prod and re-check a real screen-shared meeting

🤖 Generated with Claude Code

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 8fd8f7f6-a5fa-400a-a0cb-2a5ae334b52f

📥 Commits

Reviewing files that changed from the base of the PR and between 434c2d6 and fa8a602.

📒 Files selected for processing (2)

• src/browser/browser.ts
• src/config/env-vars.ts

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Summary by CodeRabbit

• New Features
  • Added configurable Chromium GPU modes: swiftshader, none, and legacy.
  • GPU behavior is now selectable via an environment setting, with swiftshader as the default.
  • Allows swapping GPU launch behavior across environments without rebuilding.

Walkthrough

Chromium browser startup now supports configurable GPU argument profiles. The environment schema validates BROWSER_GPU_MODE and defaults it to swiftshader; openBrowser selects the matching profile with a fallback for unrecognized values.

Changes

GPU mode configuration

Layer / File(s)	Summary
GPU mode contract and profiles src/config/env-vars.ts, src/browser/browser.ts	Defines the supported BROWSER_GPU_MODE values and Chromium argument profiles for swiftshader, none, and legacy.
Browser launch selection src/browser/browser.ts	Selects GPU arguments from the configured mode and falls back to swiftshader.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: yusuf023, amr-meetingbaas, pdrion

Poem

A rabbit sees flags in a neat little row,
Swiftshader hops where the browsers go.
“None” and “legacy” join the parade,
With defaults carefully made.
GPU carrots launch bright and true!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: restoring a working browser rasterizer for screen-share capture.
Description check	✅ Passed	The description matches the changeset and explains the browser GPU mode fix and rollout plan.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/teams-screenshare-gpu-rasterizer

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