CVE-2026-58270: Sync-in Server has a ReDoS via Unsanitized Regex in Sync Diff `pathFilters`

In the vulnerable version, the sync diff endpoint accepted a user-controlled regex pattern through pathFilters and compiled it into a RegExp without complexity validation. The resulting regex was then executed synchronously against relative file paths during diff generation.

A catastrophic-backtracking pattern, such as ^(a+)+b, can block the affected Node.js event loop when evaluated against a worst-case path shape. In a single-process deployment, this can make the server unavailable to other users while the regex evaluation is running. Repeated malicious requests can sustain the denial of service.