[Bug] Bun runtime segfault on Windows caused by astMC.dll (Hammock AssetView +) hook injection — triggered by image read operations

Summary

On Japanese enterprise Windows machines where Hammock AssetView + (an IT asset management / endpoint monitoring product widely deployed in Japan) is installed, Claude Code crashes with panic(main thread): Segmentation fault at address 0x0 whenever the assistant performs image-related operations (Read tool on an image file, or the user pastes an image into the chat).

The crash report URL from Bun consistently points to astMC.dll in the stack:

https://bun.report/1.3.13/...KERNELBASE.dll...BCSastMC.dll.../pMCSastMC.dll...UCSastMC.dll...

After decoding the URL separators, the actual faulting module is astMC.dll (the BC, pM, U prefixes are Bun crash-URL encoding delimiters, not part of the DLL name).

Environment

• OS: Windows 11 Pro (26200)
• Claude Code: v2.1.114 (also reproduced on prior v2.1.113)
• Bun (bundled): v1.3.13
• Third-party software: Hammock Corporation AssetView + / PLATINUM
• Faulting DLL: C:\Program Files (x86)\Hammock\PLATINUM\Client\{K,M}\astMC.dll
• Version on disk: 2501.102.11.1001
• Version in event log: 2501.102.11.10091
• Vendor: Hammock Corporation (https://www.hammock.jp/assetview/)

Confirming evidence — not unique to Claude Code

Windows Event Viewer (Application, Event ID 1000) records the same astMC.dll crashing another Microsoft process on the same day:

TimeCreated: 2026-04-18 18:49:10
Faulting application: MixedRealityPairingHelper.exe
Faulting module:      astMC.dll, version 2501.102.11.10091
Exception code:       0xc0000005 (access violation)

This proves the bug is in astMC.dll itself, not specific to Bun. However, Bun is hit disproportionately because AssetView + injects the DLL globally and hooks file / memory / image-decode APIs that Claude Code exercises heavily when reading images.

Reproduction

1. Install Claude Code on a Windows machine with AssetView + active
2. Start a fresh claude session
3. Ask Claude to read any PNG/JPEG file (e.g. a Playwright screenshot) or paste an image into the chat
4. Bun crashes immediately — no warm-up or long session required

Why it started suddenly

Images worked fine on 2026-04-17. Crashes began on 2026-04-18, matching an apparent silent auto-update of AssetView + that shipped a new astMC.dll build (2501.102.11.10091).

Ask

This is ultimately a vendor bug at Hammock, but:

1. Awareness — other Japanese enterprise users on Claude Code are likely affected without knowing the cause (AssetView + is common in Japan's SMB sector). A mention in docs / troubleshooting would help.
2. Resilience — if Bun could catch SEH access violations thrown by injected DLLs during image ops and report a cleaner error, users could at least identify the injecting module without decoding bun.report URLs.
3. Runtime alternative — the docs state claude.exe no longer invokes Node. Offering an opt-in Node.js runtime path (or a flag) as a fallback would help users whose enterprise EDR / asset-management tools specifically conflict with Bun's native FFI surface.

Workarounds (for other affected users)

• Do not paste / Read images inside Claude Code until AssetView is patched
• Ask IT to roll back AssetView astMC.dll to prior version (2501.102.11.1001 on disk) or exclude claude.exe / bun.exe from AssetView monitoring
• Use Claude.ai web UI for image-involving tasks