Got most of the new memory architecture roughed out.

src/c/payloads/read_stream.h

@@ -0,0 +1,34 @@
+/**
+ *  payloads/read_stream.h
+ *
+ *  A read stream.
+ *
+ *  (c) 2026 Simon Brooke <simon@journeyman.cc>
+ *  Licensed under GPL version 2.0, or, at your option, any later version.
+ */
+
+#ifndef __psse_payloads_read_stream_h
+#define __psse_payloads_read_stream_h
+
+#include <stdio.h>
+
+#include "memory/pointer.h"
+
+/**
+ * An open read stream.
+ */
+#define READTAG     "REA"
+
+/**
+ * payload of a read or write stream cell.
+ */
+struct stream_payload {
+    /** the stream to read from or write to. */
+    URL_FILE *stream;
+    /** metadata on the stream (e.g. its file attributes if a file, its HTTP
+     * headers if a URL, etc). Expected to be an association, or nil. Not yet
+     * implemented. */
+    struct cons_pointer meta;
+};
+
+#endif