TEST: insert rb_gc_start() after rb_funcall to force deterministic crash

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: samuel-williams-shopify

scheduler.c

@@ -1109,10 +1109,11 @@ VALUE rb_fiber_scheduler_blocking_operation_wait(VALUE scheduler, void* (*functi
     // after all uses of `operation` (the raw pointer derived from blocking_operation)
     // so the object cannot be moved while the raw pointer is live.
     VALUE blocking_operation = rb_fiber_scheduler_blocking_operation_new(function, data, unblock_function, data2, flags, state);
-    rb_gc_register_address(&blocking_operation);
 
     VALUE result = rb_funcall(scheduler, id_blocking_operation_wait, 1, blocking_operation);
 
+    rb_gc_start();
+
     // Get the operation data to check if it was executed
     rb_fiber_scheduler_blocking_operation_t *operation = get_blocking_operation(blocking_operation);
     rb_atomic_t current_status = RUBY_ATOMIC_LOAD(operation->status);
@@ -1124,10 +1125,6 @@ VALUE rb_fiber_scheduler_blocking_operation_wait(VALUE scheduler, void* (*functi
     operation->data2 = NULL;
     operation->unblock_function = NULL;
 
-    // All uses of blocking_operation (directly and via the `operation` pointer)
-    // are complete — safe to remove from the GC root list.
-    rb_gc_unregister_address(&blocking_operation);
-
     // If the blocking operation was never executed, return Qundef to signal the caller to use rb_nogvl instead
     if (current_status == RB_FIBER_SCHEDULER_BLOCKING_OPERATION_STATUS_QUEUED) {
         return Qundef;