Missile/jet trail position history is a fixed guest-address ring, so its
vertex fetch constants never change and the command processor's
vertex_buffer_states_ address cache skipped RequestRange forever, the GPU
copy of the trail history froze at zero (trails invisible) while CPU memory was
correct.
Register a physical-memory invalidation callback that flags when the CPU writes
watched GPU-visible memory, and drop the cached vertex-buffer states at the next
draw so the ring's pages get re-uploaded. Also notify those callbacks from the
access-violation page-recovery path (xmemory), since a recovered page becomes
read-write and would otherwise never fault again to report the write. Gated by
ac6_fix_trails (default ON).
Suspend the FPS unlock while a demo-manager Exec (DD sub_82184460 / EM sub_821856F8) ticks, so the frame-locked IngameCinematics Sequencer plays at native ~30fps instead of double speed. Adds ac6_cutscene_clamp CVar (default on).