The Find and Replace preview did not correctly reflect the rename the sync performs, and the rename engine differed from the preview engine.
- The preview rendered the literal $1 instead of the substituted capture group, because the replacement was passed straight into the regex engine, which honors \1, not the JS-style $1 the field accepts.
- The preview compiled patterns with the regex module while the live rename used stdlib re, so patterns valid in regex but not re (for example ^*) previewed a transform the sync silently skipped.
- A rename that expanded a name past the Channel.name column length aborted the whole bulk_create sync, while the preview showed the full name.
- Convert JS-style $1 backreferences to \1 via a shared helper used by both the preview and the live rename.
- Switch the live rename from re.sub to regex.sub, matching the preview engine and the sync's own include/exclude filters, with a timeout to bound catastrophic backtracking on user patterns.
- Cap the rename result at the Channel.name column length in both paths, so an over-length result cannot abort the sync.
- Add unit, integration, and differential parity tests covering the above.
