[bronze-ff]

The Builder removes its working copy of exefs before reading game files. If a locked file prevents removal, the current code ignores the error. The update path then tries to copy into an existing directory, and fresh extraction can move the new files underneath the stale directory.

Report the cleanup failure through the Builder's existing error flow, including the work path and OS error. Stop before copying or extracting so the previous game cache and saves are preserved. A missing working directory still permits a fresh build.

Refs #1354 and #1273.

Validation

• On main, the updated game-free fixture reproduced both reported Windows errors, including a copy into an existing directory and a read of nested exefs/exefs. Both paths now stop at the failed cleanup before touching the saved cache. A normal update still replaces a clearable working copy.
• The focused strict runner passed on Windows and Ubuntu under WSL for make_game_cache, lift_cleanup_error, and builder_status.
• Held a real temporary file open without delete sharing on Windows. The Builder reported WinError 32 before copying. After releasing the handle, the same update reached the fixture's lift checkpoint. All fixtures used authored temporary files.