Claude App crashes on preview_start (local preview server); Claude Code via VS Code extension unaffected

Bug report: Claude App crashes on preview_start (local preview server), Claude Code unaffected

Summary

Using Claude Code (Anthropic's CLI/agent tool) while it is hosted inside the Claude desktop/web App, calling the preview_start tool (which launches a local static file server, e.g. python -m http.server, and opens a preview browser tab) reliably crashes the App. The exact same operation, run from Claude Code via the VS Code extension, completes without issue.

Environment

• Claude Code, hosted inside the Claude App (crashes) vs. Claude Code as a VS Code extension (works)
• OS: Windows 11
• Task: local static-site preview via preview_start on a plain HTML/CSS/JS project (no framework), local Python http.server as the backing process

Steps to reproduce

1. In a Claude-App-hosted Claude Code session, work on a static website project (plain HTML/CSS/JS, no dev server framework).
2. Call the preview_start tool with a .claude/launch.json configuration that runs python -m http.server <port> --directory <path>.
3. Observe: the session/App crashes shortly after the tool call, sometimes before any further tool output is visible.

Reproduction count

• Crashed 4 out of 4 times when preview_start was called from a Claude-App-hosted session.
• Ran the identical sequence (including a preview_start call) 1 time without issue in Claude Code via the VS Code extension. Only one such run has been performed so far — not yet repeated independently in that environment.

Hypotheses tested and ruled out

1. Low disk space — system drive was at ~8.6% free at the time of the first crashes. Cleaned up to ~20% free, crash still reproduced on the next attempt. Ruled out.
2. Corrupted/malformed bundle output being served (the project's build pipeline had a byte-order-mark issue in some input files) — verified byte-for-byte that all served output files were valid UTF-8 with no BOM, before and after a fix. Crash still occurred with clean files. Ruled out.
3. File/key permission issue — investigated via Windows Event Log entries appearing around the crash window (Event ID 5061, Security-Auditing, "Microsoft Software Key Storage Provider", NTE_BAD_KEYSET return code). On inspection these keys don't exist in either the user or machine CNG key store, and the key names suggest unrelated Microsoft Edge background activity (browser tile/certificate caching for microsoft.com-family domains), not something tied to the crashing process. Inconclusive / likely unrelated red herring — not confirmed as the cause.
4. Not yet checked: whether a stale/orphaned server process from a previous preview_start call (e.g. port already in use) contributes — one clean run and one crash both involved the same port; not isolated yet.

What's confirmed

• The crash is tied specifically to preview_start (or the local server process it starts) when run from a Claude-App-hosted Claude Code session.
• It is not reproducible in Claude Code running as a VS Code extension, using the identical project, command, and port.
• It is not caused by the served content (verified clean output files) or by low disk space (ruled out after remediation).

Ask

Any pointers on what to check next (e.g., what preview_start does differently when the App hosts Claude Code vs. the VS Code extension hosting it) would help narrow this down further from our side.