set_current_layout() mutated label_'s GTK style context (remove_class/
add_class) while being called from the sway IPC worker thread via
onEvent(). Off-main-thread GTK widget mutation caused a SIGSEGV.
Record only the target layout in set_current_layout() and apply the
matching CSS class in update(), which the dispatcher runs on the GTK
main thread. A new applied_class_ member tracks the currently applied
class so update() can swap it. The shared layout_/applied_class_ state
is guarded by the existing mutex_.
Fixes#3702.
Alex
c0a26104a5