Temp spool cleanup missing

An upload service's hosts start returning 500s at 16:00 with ENOSPC; df -h shows /tmp's volume at 100%. du -sh /tmp/* reveals millions of upload-*.part files totaling the whole volume, with timestamps spread over the last three weeks. The service streams multipart uploads to a .part spool file, then renames it into place on success and is supposed to unlink it on failure. A deploy three weeks ago added an early return in the request handler's error path that skips the cleanup unlink. Upload error rate has been a steady low single-digit percent the whole time. Triage and recover.