Pass quantum to fiber_initialize instead of setting it after the call

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

Author: samuel-williams-shopify

cont.c

@@ -2369,7 +2369,7 @@ rb_fiber_storage_aset(VALUE class, VALUE key, VALUE value)
 }
 
 static VALUE
-fiber_initialize(VALUE self, VALUE proc, struct fiber_pool * fiber_pool, unsigned int blocking, VALUE storage)
+fiber_initialize(VALUE self, VALUE proc, struct fiber_pool * fiber_pool, unsigned int blocking, VALUE storage, VALUE quantum)
 {
     if (storage == Qundef || storage == Qtrue) {
         // The default, inherit storage (dup) from the current fiber:
@@ -2387,6 +2387,12 @@ fiber_initialize(VALUE self, VALUE proc, struct fiber_pool * fiber_pool, unsigne
     fiber->stack.base = NULL;
     fiber->stack.pool = fiber_pool;
 
+    if (!UNDEF_P(quantum)) {
+        uint32_t q = NUM2UINT(quantum);
+        if (q == 0) rb_raise(rb_eArgError, "quantum must be positive");
+        fiber->cont.saved_ec.quantum = q;
+    }
+
     return self;
 }
 
@@ -2450,15 +2456,7 @@ rb_fiber_initialize_kw(int argc, VALUE* argv, VALUE self, int kw_splat)
         quantum = arguments[3];
     }
 
-    fiber_initialize(self, rb_block_proc(), rb_fiber_pool_default(pool), RTEST(blocking), storage);
-
-    if (!UNDEF_P(quantum)) {
-        uint32_t q = NUM2UINT(quantum);
-        if (q == 0) rb_raise(rb_eArgError, "quantum must be positive");
-        fiber_ptr(self)->cont.saved_ec.quantum = q;
-    }
-
-    return self;
+    return fiber_initialize(self, rb_block_proc(), rb_fiber_pool_default(pool), RTEST(blocking), storage, quantum);
 }
 
 /*
@@ -2519,7 +2517,7 @@ rb_fiber_initialize(int argc, VALUE* argv, VALUE self)
 VALUE
 rb_fiber_new_storage(rb_block_call_func_t func, VALUE obj, VALUE storage)
 {
-    return fiber_initialize(fiber_alloc(rb_cFiber), rb_proc_new(func, obj), rb_fiber_pool_default(Qnil), 0, storage);
+    return fiber_initialize(fiber_alloc(rb_cFiber), rb_proc_new(func, obj), rb_fiber_pool_default(Qnil), 0, storage, Qundef);
 }
 
 VALUE