The December 20, 2025 build included LTS kernel 6.12.63, which broke system-extension merging with an overlayfs stacking-depth error (maximum fs stacking depth exceeded). Kernel 6.12.62 in the December 18 build did not show the issue.
The issue affected system-extension use; other LTS-kernel cases had not shown the same problem. The project restored the upstream kernel to stable and introduced a separate lts stream for the stable base with a longterm kernel. At publication, stable was the documented workaround for affected system-extension users.
The original investigation is recorded in issue #339.