What happens to third‑party plugins when a pytest upgrade is only partially applied?

After a pytest upgrade fails mid‑install, the environment may contain a mixture of old and new pytest files while third‑party plugins remain tied to the version they were originally installed against.

The goal is to determine whether the pytest test runner can automatically reconcile these version differences or whether manual intervention is required to restore a consistent plugin‑core set.

Does pytest automatically unload older plugin versions when core modules are upgraded? Does a force‑reinstall of pytest also reinstall plugins to matching versions? What steps are required to guarantee a consistent plugin‑core version set after a failed upgrade?