Review follow-up: `cleanupTarball` was always true (set true at init and again
in the catch), so the finally guard was dead logic. Make it meaningful — retain
the packed tarball on failure so a packaging problem can be inspected, and log
where it is; the happy path still removes it.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BrihGWcrM9JGRyu41nzZYw
c1b168e522