Following the directives given in the story.

The most important thing is that the cache should be generated by the same OPM version than the catalog.

ie. if oc-mirror is vendoring OPM v1.26.1 and the catalog was generated with OPM v1.25.4 or v1.26.8 (examples), the cache cannot be generated with OPM v1.26.1. It has to be generated by OPM v1.25.4 or v1.26.8 resp.

The case where the OPM version is too old and that the following command fails because --cache-only or --cache-dir are not supported should be handled.

opm serve /config --cache-dir /tmp/cache --cache-only

Cache integrity can be verified using --cache-enforce-integrity (runs a opm service!)