Got most of the new memory architecture roughed out.

src/c/payloads/exception.h

@@ -0,0 +1,28 @@
+/**
+ *  payloads/exception.h
+ *
+ *  An exception; required three pointers, so use object of size class 3.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __psse_payloads_exception_h
+#define __psse_payloads_exception_h
+
+#include "memory/pointer.h"
+
+/**
+ * @brief An exception; required three pointers, so use object of size class 3.
+ */
+struct exception_payload {
+  /** @brief the exception message. Expected to be a string, but may be anything printable. */
+    struct pso_pointer message;
+  /** @brief the stack frame at which the exception was thrown. */
+    struct pso_pointer stack;
+    /** @brief the cause; expected to be another exception, or (usually) `nil`. */
+    struct cons_pointer cause;
+};
+
+
+#endif