~/.claude.json corrupts repeatedly on Windows, silently wiping user-scope mcpServers

What happens

On Windows, ~/.claude.json is periodically corrupted and rewritten. Claude Code saves the damaged copy as .claude.json.corrupted.<epoch> and then continues with a config whose user-scope mcpServers is empty, silently dropping configured MCP servers (in my case: gitlab, playwright, ssh).

Evidence (my machine)

• 45 .claude.json.corrupted.* files accumulated between 2026-04-11 and 2026-07-01 (corruption on 13 distinct days).
• 4 of them are 0 bytes; the rest range up to ~90 KB.
• The current live .claude.json has mcpServers: {}, while a 2026-06-26 backup clearly contains {ssh, gitlab, playwright}.

Impact

Silent loss of configured MCP servers (and potentially other user config) with no warning surfaced in the UI. Recovery requires manually digging through the .corrupted.* backups and re-adding each server.

Environment

• OS: Windows 11 (10.0.26200.8655)
• Claude Code: 2.1.198

Suspected cause

Non-atomic / concurrent writes to the single large (~90 KB) monolithic ~/.claude.json. A crash or an overlapping write mid-serialize truncates the file (hence the 0-byte and partial copies), and the fallback path then proceeds from defaults, dropping mcpServers.

Suggested fixes

• Atomic write for ~/.claude.json (write to a temp file + rename), so a partial write never replaces the good file.
• On parse failure, auto-restore mcpServers from the last known-good backup instead of silently starting empty.
• Surface a warning in the UI when a corrupted config is detected and a .corrupted.* backup is written, so the loss isn't silent.