Mark the root context in `final_marking_phase`.
Because the root context cannot be marked from fibers.
MODIFY
src/gc.c
src/gc.c
@@ -997,6 +997,7 @@ final_marking_phase(mrb_state *mrb, mrb_gc *gc)
{
mrb_gc_mark_gv(mrb);
mark_context(mrb, mrb->c);
+ mark_context(mrb, mrb->root_c);
mrb_gc_mark(mrb, (struct RBasic*)mrb->exc);
gc_mark_gray_list(mrb, gc);
mrb_assert(gc->gray_list == NULL);

Mark the root context in `final_marking_phase`.

Because the root context cannot be marked from fibers.