My monster, it not only compiles, it now runs!

src/c/ops/stack_ops.h

@@ -0,0 +1,30 @@
+/**
+ *  ops/stack_ops.h
+ *
+ *  Operations on a Lisp stack frame.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __psse_ops_stack_ops_h
+#define __psse_ops_stack_ops_h
+
+#include "memory/pointer.h"
+#include "memory/pso4.h"
+
+/*
+ * number of arguments stored in a stack frame
+ */
+#define args_in_frame 8
+
+/** 
+ * @brief The maximum depth of stack before we throw an exception.
+ *
+ * `0` is interpeted as `unlimited`.
+ */
+extern uint32_t stack_limit;
+
+struct pso_pointer fetch_arg( struct pso4 *frame, unsigned int index );
+
+#endif