Browser Preview leaks WebView2 temp profiles: 5,577 folders / 46.5 GB in %LOCALAPPDATA%\Temp\github-app-browser-previews filled the system drive

从 canvas 和 preview 面板使用的 Browser Preview 生命周期入手，然后跟踪 %LOCALAPPDATA%\Temp\github-app-browser-previews\github-app-browser-preview-* 目录的创建。重现多个预览，并验证关闭这些预览或退出应用时会删除其 WebView2 配置文件；还要检查启动时是否会处理因崩溃而遗留的目录。

Summary

Browser Preview leaks its temporary WebView2 profile directory on every use. Each preview creates a new %LOCALAPPDATA%\Temp\github-app-browser-previews\github-app-browser-preview-XXXXXX\EBWebView\ folder (~20 MB) and never deletes it when the preview is closed or when the app exits. On my machine this accumulated 5,577 folders / 46.5 GB in ~3 days and filled the system drive to 0 bytes free, which broke unrelated software (a game could no longer write save files).

Environment

Steps to reproduce

1. Use the app normally with Browser Preview (canvas / preview panels) over a few sessions.
2. Open %LOCALAPPDATA%\Temp\github-app-browser-previews\.
3. Observe one github-app-browser-preview-<random> folder per preview, each containing a full EBWebView profile (cache, IndexedDB, GPU cache, etc.), none of which are removed.

Measurements

PS> (Get-ChildItem "$env:LOCALAPPDATA\Temp\github-app-browser-previews" -Force).Count
5577

PS> Get-ChildItem "$env:LOCALAPPDATA\Temp" -Force | sort by size
   GB Name                        Modified
----- --------------------------- --------------------
46.47 github-app-browser-previews 9/14/2026 9:02:17 PM
 0.51 DLSS5-Swapper
 0.18 Highlights
 ...

Every folder had a LastWriteTime between 2026-09-11 and 2026-09-14, i.e. this is ~12 GB/day of growth under normal use. Each folder is roughly 20 MB and contains only EBWebView\ (the WebView2 user-data dir).

Deleting all folders older than 30 minutes freed 47.7 GB and the app kept working normally, so nothing in there is needed after the preview is closed.

Expected behavior

• Closing a Browser Preview (or exiting the app) should delete its github-app-browser-preview-* user-data directory.
• Ideally, on startup the app should also sweep stale directories left over from a crash.
• Alternatively, reuse a single persistent user-data dir per app instance instead of creating a new one per preview.

Actual behavior

Directories are created per preview and never removed. Disk usage grows unbounded until the system drive is full.

Workaround

Get-ChildItem "$env:LOCALAPPDATA\Temp\github-app-browser-previews" -Force |
  Where-Object { $_.LastWriteTime -lt (Get-Date).AddMinutes(-30) } |
  Remove-Item -Recurse -Force

Filed by Copilot on behalf of the user, from a Copilot chat session that diagnosed the full disk.