v5.9.0-LTS — P0.1 CLOSED

P0.1 CLOSED — the intermittent ring-3 [fault] was a preemptible CR3-switch→iretq window in the syscall-exit path, fixed with a single cli. LTS release.

Also includes: 3 GUI highs (paint divide-by-zero, menu hit-test skew, fb backbuffer repoint, level-triggered menus), VFS fd refcounts, ext2 write-path overhaul verified by e2fsck (9 defects), editor truncation guard, full audit/hardening (ELF bounds, user_v2p, FMASK, cld, TSS struct, 22-pixel GUI offset, framebuffer clipping, dynamic linker, fork isolation with mprotect), SMP stages (per-CPU TSS, user procs on APs, spinlocks, TLB shootdown IPIs), thread/fd table coherence, and the full rc1-rc17 arc.