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MCP filesystem server silently wrote to the wrong path when handed a Windows drive path on POSIX
PR #4704 in modelcontextprotocol/servers, merged 2026-08-30, fixes issue #4686: on POSIX hosts a path like `C:\Users\me\notes\file.md` was treated as a relative filename inside the allowed directory, so the write reported success while landing somewhere else entirely. The 13-line fix rejects drive-letter forms before relative path resolution on POSIX only, leaving Windows behavior unchanged, with a regression test. Anyone running the reference filesystem server with cross-platform agents should pull this.
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