Unclear What decides whether the safer write is used is not stated.
What
Before an mcp_call request runs a tool, Claude Code stages its input as files on disk. When a check passes, it now writes these files under the folder's real, fully resolved location instead of writing them directly. A failure is reported as "input stage failed".
Why
This guards against a symlink (a file that points to another place on disk) being changed to point somewhere else, so staged input cannot be redirected to an unexpected location.
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What decides whether the safer write is used is not stated.