Right, I'm committing this session because I'm too cold and tired to go on.

It does not at present build (and it's going to take a good bit more work
before it does).

src/c/payloads/write_stream.h

@@ -13,6 +13,7 @@
 /* write stream shares a payload with /see read_streem.h */
 
 #include "io/fopen.h"
-struct pso_pointer make_write_stream( URL_FILE * output,
+struct pso_pointer make_write_stream( struct pso4 *frame_pointer,
+                                      URL_FILE * output,
                                       struct pso_pointer metadata );
 #endif