GHSA-R5JH-Q2MW-GCX4 Fission: SanitizeFilePath lexical HasPrefix bypass permits sibling-directory escape

SanitizeFilePath in pkg/utils/utils.go validated that a path stayed under a safe directory by calling strings.HasPrefixpath, safedir. This is a lexical check, not a directory boundary check: /packages-extra/evil starts with /packages, so it passed. The function did not enforce a path-separator...