The missing code in question, which amounted to just a handful of lines, is particularly interesting because unlike the rest of the collision-detection code which uses the logical playfield, it actually inspects pixels rendered during the draw_player_sprite() routine. This will have ramifications for ports to sprite-only systems, like the Neo Geo, and will likely require that the port maintains the bitmap screens in system memory even though they aren't used for the actual display.
Here's a video of the demo mode running for the 1st level:
That aside, the end result is that Lode Runner is now complete in the sense that it is 100% playable on the Coco 3. There are a few bells and whistles that have yet to be ported, so whilst I work on those I thought I'd release a playable demo for beta testing.
Please read the included README.TXT file before submitting any comments, suggestions and/or bug reports, but feedback is most welcome.
Without further ado, here's a link for an archive with the DSK file.
EDIT: I should add that I'm yet to run this on a real Coco! I plan to do that sometime this week!
UPDATE: I've fixed the problem with not being able to exit the demo. Please re-download.