[BUG] Cowork: Persistent RPC "message too large: 2065853797 bytes" on every launch — constant across all local cleanup (Windows)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Cowork fails on every launch with the same RPC error in cowork-service.log:
[Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
The byte count (2065853797 ≈ 1.92 GiB) is identical on every launch and brushes the ~2 GiB RPC message ceiling, tearing down the persistent control connection. Symptoms downstream: workspace shows "Failed to start" / "VM connection timeout," MCP filesystem connection drops, and the client spins retrying the pipe at ~90%+ CPU.
The payload is account/session-state-derived, not local data. I verified this exhaustively — the byte count never changed across any of the following:

Removing connected folders from the project's spaces.json
Trimming all heavy task transcripts (removed the 6 largest local_* task folders, ~122 MB)
Repointing connected folders to a clean local path
Deleting sessiondata.vhdx (fresh empty session disk regenerated) — same bytes
Launching with zero projects — same bytes

Total on-disk project data is only ~188 MB; connected folders ~40 MB. Nothing locally is anywhere near 1.92 GB. The message is assembled internally and there is no user-facing way to scope or reduce it.

What Should Happen?

Cowork should bound or chunk the session-state RPC payload so it never exceeds the message cap, and degrade gracefully rather than crash-loop.

Related: behavior resembles the RPC-drop family (#40392, #29848) but with a specific, constant oversized-message size rather than an EOF/abort.

Error Messages/Logs

2026/06/22 20:01:42.921253 [VM] Creating HCS compute system...
2026/06/22 20:01:42.921253 [HCS] Calling HcsCreateComputeSystem with id=cowork-vm-96109d8c
2026/06/22 20:01:42.922252 [HCS] Config JSON:
{"Owner":"cowork-vm-96109d8c","SchemaVersion":{"Major":2,"Minor":2},"ShouldTerminateOnLastHandleClosed":true,"VirtualMachine":{"Chipset":{"LinuxKernelDirect":{"InitRdPath":"C:\\Users\\dsusca\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\initrd","KernelCmdLine":"console=ttyS0 earlyprintk=serial root=/dev/sda1 rootfstype=ext4 rw panic=10","KernelFilePath":"C:\\Users\\dsusca\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\vmlinuz"}},"ComputeTopology":{"Memory":{"AllowOvercommit":true,"SizeInMB":4096},"Processor":{"Count":2}},"Devices":{"HvSocket":{"HvSocketConfig":{"DefaultBindSecurityDescriptor":"D:P(A;;FA;;;WD)","DefaultConnectSecurityDescriptor":"D:P(A;;FA;;;WD)","ServiceTable":{"00000400-facb-11e6-bd58-64006a7986d3":{"AllowWildcardBinds":true,"BindSecurityDescriptor":"D:P(A;;FA;;;WD)","ConnectSecurityDescriptor":"D:P(A;;FA;;;WD)"},"0000c822-facb-11e6-bd58-64006a7986d3":{"AllowWildcardBinds":true,"BindSecurityDescriptor":"D:P(A;;FA;;;WD)","ConnectSecurityDescriptor":"D:P(A;;FA;;;WD)"}}}},"Plan9":{},"Scsi":{"Primary SCSI Controller":{"Attachments":{"0":{"Path":"C:\\Users\\dsusca\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\rootfs.vhdx","Type":"VirtualDisk"},"1":{"Path":"C:\\Users\\dsusca\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\smol-bin.vhdx","ReadOnly":true,"Type":"VirtualDisk"},"2":{"Path":"C:\\Users\\dsusca\\AppData\\Roaming\\Claude\\vm_bundles\\claudevm.bundle\\sessiondata.vhdx","Type":"VirtualDisk"}}}},"VirtioSerial":{"Ports":{"0":{"Name":"claude-daemon-console","NamedPipe":"\\\\.\\pipe\\cowork-daemon-console-cowork-vm-96109d8c"}}}}}}
2026/06/22 20:01:42.922252 [HCS] Created operation handle: 3045996647392
2026/06/22 20:01:44.621760 [HCS] HcsCreateComputeSystem returned: hr=0x0, handle=3045996648080, lastErr=The operation completed successfully.
2026/06/22 20:01:48.878925 [HCS] HcsWaitForOperationResult returned: hr=0x0
2026/06/22 20:01:48.878925 [HCS] Result JSON: (nil)
2026/06/22 20:01:48.911005 [HCS] HcsGetComputeSystemProperties returned: hr=0x0
2026/06/22 20:01:49.261008 [HCS] Properties result: {"Id":"cowork-vm-96109d8c","SystemType":"VirtualMachine","Owner":"cowork-vm-96109d8c","RuntimeId":"217421ee-4242-58e8-aece-4cc5baa5387b"}
2026/06/22 20:01:49.261008 [VM] Got VM runtime ID: 217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:49.261008 [VM] Starting RPC server for vsock connections...
2026/06/22 20:01:49.261008 [HVSock] Creating listener:
2026/06/22 20:01:49.261008 [HVSock]   VMID: 217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:49.261008 [HVSock]   Port: 51234 (0xc822)
2026/06/22 20:01:49.261008 [HVSock]   ServiceGUID: 0000c822-facb-11e6-bd58-64006a7986d3
2026/06/22 20:01:49.286020 [HVSock] Listening on port 51234 (service GUID: 0000c822-facb-11e6-bd58-64006a7986d3)
2026/06/22 20:01:49.286020 [RPC] Server started, waiting for sdk-daemon connection on port 51234
2026/06/22 20:01:49.286020 [HVSock] Creating listener:
2026/06/22 20:01:49.286020 [HVSock]   VMID: 217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:49.286020 [HVSock]   Port: 1024 (0x400)
2026/06/22 20:01:49.286020 [HVSock]   ServiceGUID: 00000400-facb-11e6-bd58-64006a7986d3
2026/06/22 20:01:49.286020 [HVSock] Listening on port 1024 (service GUID: 00000400-facb-11e6-bd58-64006a7986d3)
2026/06/22 20:01:49.286020 [VNet] Listening for VM network connections on vsock port 1024
2026/06/22 20:01:50.339836 [VM] Granted VM access to: C:\Users\dsusca\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\rootfs.vhdx for NT VIRTUAL MACHINE\217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:50.528765 [VM] Granted VM access to: C:\Users\dsusca\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\vmlinuz for NT VIRTUAL MACHINE\217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:50.608546 [VM] Granted VM access to: C:\Users\dsusca\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\initrd for NT VIRTUAL MACHINE\217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:50.687762 [VM] Granted VM access to: C:\Users\dsusca\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\smol-bin.vhdx for NT VIRTUAL MACHINE\217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:50.786974 [VM] Granted VM access to: C:\Users\dsusca\AppData\Roaming\Claude\vm_bundles\claudevm.bundle\sessiondata.vhdx for NT VIRTUAL MACHINE\217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:50.786974 [VM] Starting compute system...
2026/06/22 20:01:50.788971 [HCS] HcsStartComputeSystem returned: hr=0x0, lastErr=The operation completed successfully.
2026/06/22 20:01:52.756792 [VM] Adding Plan9 share via HcsModifyComputeSystem: name=c path=C:\ port=9902 flags=0x10 hasToken=true
2026/06/22 20:01:52.756792 [HCS] Calling HcsModifyComputeSystem
2026/06/22 20:01:52.756792 [HCS] Config: {"ResourcePath":"VirtualMachine/Devices/Plan9/Shares","RequestType":"Add","Settings":{"Name":"c","AccessName":"c","Path":"C:\\","Port":9902,"Flags":16}}
2026/06/22 20:01:52.799514 [HCS] HcsModifyComputeSystem returned: hr=0x0, lastErr=The operation completed successfully.
2026/06/22 20:01:52.808841 [VM] Adding Plan9 share via HcsModifyComputeSystem: name=z path=Z:\ port=9925 flags=0x10 hasToken=true
2026/06/22 20:01:52.808841 [HCS] Calling HcsModifyComputeSystem
2026/06/22 20:01:52.808841 [HCS] Config: {"ResourcePath":"VirtualMachine/Devices/Plan9/Shares","RequestType":"Add","Settings":{"Name":"z","AccessName":"z","Path":"Z:\\","Port":9925,"Flags":16}}
2026/06/22 20:01:52.809707 [HCS] HcsModifyComputeSystem returned: hr=0x0, lastErr=The operation completed successfully.
2026/06/22 20:01:52.811887 [VM] Starting daemon console reader: pipe=\\.\pipe\cowork-daemon-console-cowork-vm-96109d8c log=C:\ProgramData\Claude\Logs\coworkd\user-S-1-5-21-3584526160-3173429229-3341185249-1001.log
2026/06/22 20:01:52.812263 [VM] VM started successfully
2026/06/22 20:01:52.835696 [Console] Connected to daemon console pipe: \\.\pipe\cowork-daemon-console-cowork-vm-96109d8c
2026/06/22 20:01:58.100382 [HVSock] Accepted connection from VM=217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:01:58.100382 [VNet] VM network connected from 217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:02:01.354597 [HVSock] Accepted connection from VM=217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:02:01.354597 [RPC] sdk-daemon connected from VM 217421ee-4242-58e8-aece-4cc5baa5387b
2026/06/22 20:02:01.357240 [RPC] Network status: CONNECTED
2026/06/22 20:02:01.357758 [VM] Network status: CONNECTED
2026/06/22 20:02:01.357758 [RPC] sdk-daemon is ready
2026/06/22 20:02:01.357758 [VM] sdk-daemon is ready!
2026/06/22 20:02:01.357758 [VM] Sent plan9Shares notification (2 shares)
2026/06/22 20:02:01.374663 [Certs] Loaded 38 CA certificates from CurrentUser\ROOT
2026/06/22 20:02:01.385662 [Certs] Loaded 3 CA certificates from CurrentUser\CA (5 untrusted skipped)
2026/06/22 20:02:01.391216 [Certs] Loaded 0 CA certificates from LocalMachine\ROOT
2026/06/22 20:02:01.391216 [Certs] Loaded 0 CA certificates from LocalMachine\CA (5 untrusted skipped)
2026/06/22 20:02:01.391216 [Certs] Loaded 41 unique CA certificates from Windows ROOT+CA stores
2026/06/22 20:02:01.391216 [RPC] Sending 41 CA certificates for installation
2026/06/22 20:02:03.472308 [VM] Installed 41 CA certificates in guest
2026/06/22 20:02:03.751020 [RPC] API reachability: REACHABLE
2026/06/22 20:02:03.751565 [VM] API reachability: REACHABLE
2026/06/22 20:02:54.988754 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:02:54.988754 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:03:00.013485 [Server] Client connected
2026/06/22 20:03:13.774837 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:03:16.751882 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:03:16.752882 [Server] Persistent RPC: entering loop
2026/06/22 20:03:24.670269 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:03:24.707269 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:03:28.288963 [Server] Client connected
2026/06/22 20:03:49.141823 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:03:51.167138 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:03:51.167138 [Server] Persistent RPC: entering loop
2026/06/22 20:04:32.137434 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:04:32.137434 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:04:34.527724 [Server] Client connected
2026/06/22 20:04:47.934921 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:04:48.877413 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:04:48.920417 [Server] Persistent RPC: entering loop
2026/06/22 20:04:57.178345 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:04:57.178345 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:04:58.852715 [Server] Client connected
2026/06/22 20:05:10.218448 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:05:10.860452 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:05:10.860452 [Server] Persistent RPC: entering loop
2026/06/22 20:05:19.888520 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:05:19.888520 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:05:23.621762 [Server] Client connected
2026/06/22 20:05:39.379186 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:05:40.752277 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:05:40.769270 [Server] Persistent RPC: entering loop
2026/06/22 20:05:46.417613 [Server] Persistent RPC: connection ended: message too large: 2065853797 bytes
2026/06/22 20:05:46.417613 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:05:51.633966 [Server] Client connected
2026/06/22 20:06:00.889610 [Server] Client signature verified: C:\Program Files\WindowsApps\Claude_1.14271.0.0_x64__pzs8sxrjxfjjc\app\claude.exe (subject: Anthropic, PBC)
2026/06/22 20:06:00.928535 [Server] Client connected: user=dsusca exe=claude.exe isDev=false
2026/06/22 20:06:00.928535 [Server] Persistent RPC: entering loop
2026/06/22 20:06:01.397517 Service stop requested
2026/06/22 20:06:01.397517 Shutdown signal received...
2026/06/22 20:06:01.397517 [Server] Stopping server...
2026/06/22 20:06:01.397517 [Server] Event subscriber disconnected for dsusca:C:\Users\dsusca\AppData\Roaming\Claude (remaining: 0)
2026/06/22 20:06:02.965531 [Server] Persistent RPC: connection ended: failed to read length: EOF
2026/06/22 20:06:02.965531 [Server] Session dsusca:C:\Users\dsusca\AppData\Roaming\Claude has no active connections, idle timeout starts
2026/06/22 20:06:02.965531 [Server] Stopping VM for session dsusca:C:\Users\dsusca\AppData\Roaming\Claude...
2026/06/22 20:06:02.965531 [VM] Stopping VM...
2026/06/22 20:06:02.966724 [VM] Graceful shutdown failed, forcing termination: HcsShutdownComputeSystem failed with HRESULT 0x0/0x80070032
2026/06/22 20:06:02.972246 [VNet] VM network connection ended: cannot receive packets from 217421ee-4242-58e8-aece-4cc5baa5387b, disconnecting: cannot read size from socket: An established connection was aborted by the software in your host machine.
2026/06/22 20:06:02.972785 [RPC] Read error: failed to read length: An established connection was aborted by the software in your host machine.
2026/06/22 20:06:02.972785 [RPC] sdk-daemon disconnected
2026/06/22 20:06:02.978826 [Console] Daemon console read error: No process is on the other end of the pipe.
2026/06/22 20:06:03.209099 [VM] Releasing VM resources...
2026/06/22 20:06:03.209099 [VM] Stopping console reader (VM no longer running)...
2026/06/22 20:06:03.211092 [VNet] Virtual network stopped
2026/06/22 20:06:03.212097 [RPC] Server stopped
2026/06/22 20:06:03.212097 [VM] VM stopped
2026/06/22 20:06:03.212097 [Server] Server stopped
2026/06/22 20:06:03.212097 Service stopped.

Steps to Reproduce

open the Claude desktop in windows.

that is all.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Desktop 1.14271.0.0 (x64, MSIX/Store install)

Platform

Claude Desktop

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Host is Windows 10 running as a guest under QEMU/KVM (nested virtualization). The nested VM boots and connects normally every time - sdk-daemon is ready and API reachability: REACHABLE both appear in the log before the oversized message fires - so this is a host-side serialization issue, not a VM/virtualization failure.