Parquet files unreadable after upgrade

A nightly job writes Parquet files to your data lake; downstream Spark/Trino jobs read them for reporting. After a library bump in the writer image at 01:00, last night's partitions write fine and a few readers succeed, but most reader jobs fail with 'unsupported/unknown compression codec' or read garbage column values, while older partitions read perfectly. Dashboards: writer job exit code 0, file counts and sizes look normal in object storage. How do you triage, stop producing unreadable partitions, and recover the data?