Wow. Courtesy of jvprat, the mansion is now navigable. This is not *that* big a step from where we were before, but it feels enormous because it actually makes the game at least partially playable (whereas before we essentially just had a movie player). As you can see, the engine also compiled on Windows CE with no changes at all.
There is still plenty left for us to do: the MIDI music, save games and, well, the puzzles. But this is so exciting!