question - where is this used - the usually graceful exit is the followup to a broken plugin at least in the apps im aware of

You are right to ask for a concrete consumer. I searched the local source/docs and found no project call site that catches PluginValidationError and then continues registration: load_setuptools_entrypoints() propagates it, and the common host behavior is to exit.

The change was prompted by the existing register() XXX about returning with changed state, not by a reported downstream recovery failure. The focused test is valid in the project environment (tox -e py311 -- testing/test_pluginmanager.py -q: 44 passed), but it only establishes the invariant and not a demonstrated consumer need.

I therefore do not want to overstate this as a bug fix. If maintaining atomic registration is not a desired API invariant, I am happy to close the PR rather than add behavior without a concrete caller.

"You are right to push back on this" is a classic AI line.

closing as unattended ai