[BUG] Cold-start AppHangXProcB1 on Win 11 Home 25H2 — "YukonSilver not supported" + Claude Code binary not found

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?

Claude Desktop hangs frequently with AppHangXProcB1 (cross-process hang) on cold-start scenarios — boot, new session, or after idle. 17 hangs in 7 days. A coworker on Windows 11 Pro with the same workflow shows 0 hangs in 90 days.

main.log reveals three concurrent issues that may compound to exceed Windows' 5-second hang threshold:

1. "YukonSilver not supported" — Cowork VM warm download is skipped with a Korean error message saying "the latest installer is required" (user is already on the latest official installer).

1. "Claude Code native binary not found" ReferenceError — fired even though the binary exists at the exact reported path and is currently running. Appears to be a path-resolution race condition.

1. 403 + Cloudflare Turnstile loop on every Desktop launch — https://claude.ai/api/challenge_redirect and https://claude.ai/ both return 403 with Turnstile challenge.

The hang pattern: Claude works briefly (~1-2 min after cold start) then hangs. Active sessions that have been continuously used do not hang.

What Should Happen?

Claude Desktop should:

1. Detect unsupported environments at startup and run gracefully in chat-only mode without repeatedly attempting Cowork/VM init.
2. Resolve the Claude Code binary path correctly without false "not found" errors when the binary exists and is running.
3. Not exceed the Windows 5-second hang threshold during cold-start or new-session scenarios on supported Windows builds.
4. Provide a clear UI path for users to diagnose/disable problematic features like Cowork on incompatible setups (Windows 11 Home, etc.).

Error Messages/Logs

========== From %APPDATA%\Claude\logs\main.log ==========

2026-04-29 12:33:43 [info] [warm] Skipping VM warm download - YukonSilver not supported (Cowork를 사용하려면 최신 설치 프로그램으로 Claude Desktop을 설치해야 합니다)

error: ReferenceError: Claude Code native binary not found at C:\Users\<USER>\AppData\Roaming\Claude\claude-code\2.1.121\claude.exe. Please ensure Claude Code is installed via native installer or specify a valid path with options.pathToClaudeCodeExecutable.
    at onErrorNT (node:internal/child_process:508:16)
    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

[info] Navigation to https://claude.ai/api/challenge_redirect?to=https%3A%2F%2Fclaude.ai%2Fepitaxy failed with status code 403
[info] Turnstile iframe detected. Removing error overlay.
[info] Navigation to https://claude.ai/ failed with status code 403

========== From Windows Event Log (Application) ==========

Event Type: AppHangXProcB1 (cross-process hang)
Provider: Windows Error Reporting
Subject process: claude.exe (versions 1.5220.0.0 and 1.5354.0.0)
Frequency: 17 occurrences in 7 days

Also recorded: RADAR_PRE_LEAK_64 on ccSvcHst.exe (SEP) — likely environmental, not caused by Claude.

Steps to Reproduce

1. Install Claude Desktop on Windows 11 Home 25H2 (Build 26200.x).
2. Have corporate security software active (Symantec Endpoint Protection + Korean enterprise DRM such as SoftCamp Document Security Client).
3. Reboot the PC.
4. Wait until login.
5. Launch Claude Desktop (or let it auto-start).
6. Either:

a) Wait 30+ seconds without interacting, then start a chat → hang
b) Start chatting briefly (~1-2 min), then open a new session → hang
c) After cold-starting, click anywhere requiring Code spawn → hang

1. Windows Event Log shows AppHangXProcB1 events.

Active sessions that have been continuously used do NOT hang. The issue is specifically cold-start / first-IPC scenarios.

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.121 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Environment

| Item | Value |
|---|---|
| OS | Windows 11 Home 25H2 (Build 26200.8246) |
| Hardware | LG gram 15Z90Q-GA5HK / Intel i5-1240P / 16GB RAM / NVMe SSD |
| Claude Desktop | 1.5354.0.0 (also reproduced on 1.5220.0.0) |
| Claude Code | 2.1.121 |
| Domain Status | Not domain-joined (WORKGROUP) |
| Windows Install Age | 503 days (stable, no recent format) |
| Corporate Security | Symantec Endpoint Protection 14.3.7393.4000, SoftCamp Document Security Client 5.0 |
| Active Filesystem Minifilters | 19 (incl. SCShield, BHDrvx64, SymEvnt, SRTSP, SymEFASI, PISecSmartDrv, FileCrypt, CldFlt) |

Boot Timeline (security tools come online over ~3.5 minutes)