resolveLaunchSurface function

DVLaunchOutcome resolveLaunchSurface({ required Set<DVRenderSurface> linked, required List<String> arguments, required bool displayAvailable, bool interactive = true, })

Decides where a launch should start.

linked is what the build actually contains — resolved at build time from the -cli/-tui suffix or a dartvel.terminal opt-in, never probed here.

The rules, in order:

1. One backend means no decision. A GUI-only build starts the GUI and fails to find a display exactly as it does today; an application that opted into nothing gains no prompt, no flag and no branch.
2. --tui starts the terminal. The explicit path, and the one to reach for over SSH.
3. A display means the GUI. A terminal is where the command was typed, not necessarily where the application belongs.
4. No display, and someone is there to answer: ask. Both silent answers are wrong — quietly redrawing as text is indistinguishable from a bug at the moment it happens, and failing outright wastes a capability the application was built with.
5. No display and nobody to ask: take the terminal. A prompt with no human at the other end is a hang, and the terminal is the only surface that can work.

Implementation

DVLaunchOutcome resolveLaunchSurface({
  required Set<DVRenderSurface> linked,
  required List<String> arguments,
  required bool displayAvailable,
  bool interactive = true,
}) {
  if (linked.isEmpty) {
    throw ArgumentError.value(
      linked,
      'linked',
      'A build must contain at least one rendering backend. An empty set is a '
          'build configuration error, not a runtime condition.',
    );
  }

  final hasTerminal = linked.contains(DVRenderSurface.terminal);
  final hasGui = linked.contains(DVRenderSurface.gui);

  if (!hasTerminal) return DVLaunchOutcome.gui;
  if (!hasGui) return DVLaunchOutcome.terminal;

  if (arguments.contains('--tui')) return DVLaunchOutcome.terminal;
  if (displayAvailable) return DVLaunchOutcome.gui;
  return interactive
      ? DVLaunchOutcome.askToUseTerminal
      : DVLaunchOutcome.terminal;
}