[Bug] Cowork VM sandbox disk exhaustion: yes.exe output unbounded to VHDX without size limits

Bug Description
bug | Area: Cowork VM sandbox (desktop app)

Details:

• What happened: System froze; yes.exe (Git-for-Windows MSYS2) ran with no manual invocation, wrote continuously until C: free space dropped from 20GB to 5-6GB (~14GB). No matching flat file found on host filesystem by extension/size/timestamp search.
• What the user said: "my system froze and yes.exe launched completely on its own in the background... continuously wrote data to disk... dropping my C: drive free space from 20GB down to 5-6GB." Then: "ur a agent, find out what happened for me."
• Repro: CoworkVMService (DisplayName "Claude", LocalSystem, cowork-svc.exe) installed/started at incident time. Boots Linux micro-VM (vmlinuz+initrd via Hyper-V vmcompute), root filesystem backed by dynamically-expanding rootfs.vhdx at %LOCALAPPDATA%\Packages\Claude_\LocalCache\Roaming\Claude\vm_bundles\claudevm.bundle\rootfs.vhdx. VHDX write timestamps matched incident window (7.6GB now, after apparent auto-recovery already trimmed it). yes.exe LastAccessTime matched same window — yes ran inside a Cowork VM session, redirected to a file, and the VM's disk growth showed up on host as VHDX growth — invisible to normal big-file search since it's a virtual disk image, not a flat dump.
• Evidence: Service CoworkVMService, binary C:\Program Files\WindowsApps\Claude_2.2553.1.0_x64__pzs8sxrjxfjjc\app\resources\cowork-svc.exe; event log 2026-09-20 15:09:49-15:09:50 (service install/start), 15:11:17-15:11:28 (rootfs.vhdx + .origin rewrites); yes.exe LastAccessTime 15:13:54.
• Cause: Not fully confirmed (VM session contents gone after reset) but strongly indicated — agent/Cowork task inside sandbox ran yes redirected to a file instead of piped to a consumer, and the VHDX had no apparent size cap, letting it balloon before something reset the bundle.

Environment Info

• Platform: win32
• Terminal: null
• Version: 2.1.278
• Feedback ID: cb65f8a3-db37-456a-b309-4acb493c7cbd

Errors

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Start with CoworkVMService and cowork-svc.exe, then trace how the VM bundle's rootfs.vhdx is created and expanded under the Claude package LocalCache. Reproduce a Cowork VM task that runs yes.exe with redirected output and observe VHDX growth. Done means unbounded guest writes cannot exhaust the host disk and the behavior is covered by an appropriate regression check.