[z-machine] "State of play" for restart/restore

[David Kinder]

> Does anyone have comments on what gets restarted other than the game
> memory? All the stuff like output_stream, input_stream, buffer_mode,
> which window you're writing to and what its dimensions are, that kind
> of stuff. The spec does say you'll have to rewrite the status line, but
> I'm looking for a bit more detail on this issue. From looking at a
> couple interpreters, it looks like different ones restart different
> things.

Section 6 of the spec defines what it means by "the state of play",
which is what is restored. The obvious reading of that section is that
games cannot rely on anything not defined in the state of play, like
streams. In fact, in the remarks section at the end:

  Note that the "state of play" does not include numerous input/output
  settings (the current window, cursor position, splitness or otherwise,
  which streams are selected, etc.)

Which seems to cover the issue.

David