[BUG] Cowork Windows: SDK 2.1.260 fails .verified check consistently even after full VM/SDK rebuild; auto-reinstall gated behind same error

What's Wrong?

Cowork fails to start with RPC error -1: SDK version 2.1.260 not verified at /mnt/.virtiofs-root/shared/c/Users/.../claude-code-vm/2.1.260/.verified, consistently, even after a full clean rebuild of both the VM bundle and the SDK download.

Environment

• Claude Desktop 1.49585.0.0, Windows 11 Pro build 26200, x64
• SDK version affected: 2.1.260
• AppData at default location (C:\Users\<user>\AppData\Local), no redirection, no symlinks

What was verified/ruled out as cause

1. Binary integrity - SHA256 of downloaded claude binary matches .payload exactly on every retry (7a2fdc74b6836ea3d183f665b869f0ee3baebc9713cbebffe5838da4ea7bd82e, size 214687216 bytes).
2. File permissions on .verified - correct ACL (SYSTEM, Administrators, user all FullControl).
3. Authenticode signature of claude.exe and cowork-svc.exe - both Valid.
4. HCS/vmcompute state - found and cleared a zombie VM object persisting the same RuntimeId across multiple app-level restarts (confirmed via hcsdiag list / hcsdiag kill). This was itself contributing to a separate Plan9 "invalid argument" failure (matches #25132 / #31632 pattern), resolved by restarting vmcompute.
5. Host memory - plenty free (12+ GB) at time of failure, ruling out OOM-related guest kernel death (which was a real, separate issue earlier in the same session at low memory; resolved by freeing RAM).
6. Full rebuild - deleted vm_bundles and claude-code-vm folders entirely, forcing complete redownload from scratch. Same .verified content (ad1c0b3f2de334f4bcb4a783c275b1af7a5945c0c955a9c7352cf4fa0666a7ec) and same error reproduced identically.
7. Checked the JesperLive/ClaudeFix community toolkit and Jonas Kamsker's write-up - neither documents this specific .verified mismatch; both cover Plan9/NAT/HCS failures which were separate issues already resolved on this machine.

Key observation

The .verified file content is byte-identical across every fresh redownload, which suggests the verification value served by the backend for build 2.1.260 does not match what the guest VM's validation logic expects - this looks like a backend/build-side mismatch rather than a client-side integrity or permissions issue.

Secondary bug confirmed

Skipping auto-reinstall (already attempted once) blocks the only automatic recovery path after the first failure, matching the same pattern reported in #31632 and #90283. This forces manual folder deletion on every single attempt since the "Reinstall workspace" button is gated behind the same failure condition it exists to fix.

Steps to Reproduce

1. Open Claude Desktop, go to Cowork tab.
2. Attempt to start a workspace with SDK 2.1.260.
3. Error: RPC error -1: SDK version 2.1.260 not verified at .../claude-code-vm/2.1.260/.verified
4. Delete %LOCALAPPDATA%\Claude-3p\claude-code-vm and %LOCALAPPDATA%\Claude-3p\vm_bundles, restart Claude.
5. Same error reproduces identically after full redownload.

What Should Happen?

Cowork should start successfully, or at minimum the auto-reinstall/recovery path should not be gated behind the same error condition it is meant to resolve.

Error Messages/Logs

2026-09-10 21:40:31 [error] [VM:start] Startup failed: Error: RPC error -1: SDK version 2.1.260 not verified at /mnt/.virtiofs-root/shared/c/Users/sgomi/AppData/Local/Claude-3p/claude-code-vm/2.1.260/.verified
    at Socket.<anonymous> (C:\Program Files\WindowsApps\Claude_1.49585.0.0_x64__pzs8sxrjxfjjc\app\resources\app.asar\.vite\build\index.chunk-BRN0sgAk.js:13:1513253)
    at Socket.emit (node:events:514:28)
    at addChunk (node:internal/streams/readable:567:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:518:3)
    at Readable.push (node:internal/streams/readable:398:5)
    at Pipe.onStreamRead (node:internal/stream_base_commons:189:23) {
  [message]: 'RPC error -1: SDK version 2.1.260 not verified at /mnt/.virtiofs-root/shared/c/Users/sgomi/AppData/Local/Claude-3p/claude-code-vm/2.1.260/.verified'
}
2026-09-10 21:40:31 [info] [VM:start] Skipping auto-reinstall (already attempted once)

Is this a regression?

Unknown - Cowork worked previously on this machine before a CoworkVMService crash/recovery incident (unrelated to this specific SDK verification issue) required manual vmcompute and HCS cleanup.

Platform

Anthropic API

Operating System

Windows

2026-09-02 19:26:48  version=2.1.255
2026-09-04 09:13:51  version=2.1.255
2026-09-09 19:00:15  version=2.1.258   <- first appearance
2026-09-09 19:01:42  version=2.1.258
2026-09-09 19:07:35  version=2.1.260   <- first appearance, 6 minutes after 2.1.258
2026-09-09 19:07:51  version=2.1.260   (all subsequent attempts, including today, stuck on 2.1.260)