- The `libcxxhardeningextensive` hardening flag has been **disabled** by default. Enabling it by default in 25.11 was unintentional and may have had a negative effect on performance in some cases. `libcxxhardeningfast` remains enabled by default.
- The packages `ibtool`, `actool` and `re-plistbuddy` have been added, providing reimplementations of the corresponding proprietary Apple tools. They are more compatible with the originals than the previously existing `xcbuild` package, and should enable more darwin software to be built from source.
- Switch inhibitors were introduced, which add a pre-switch check that compares a list of strings between the previous and the new generation, and refuses to switch into the new generation when there is a difference between the two lists. This allows to avoid switching into a system when for instance the systemd version changed by adding `config.systemd.package.version` to the switch inhibitors for your system. You can still forcefully switch into any generation by setting `NIXOS_NO_CHECK=1`.
