Scripts

Does anyone have a suggestion for how to determine, using scripts, which game mode is running: multiplayer or single-player?

Ask the player directly in a message at the start of the map. Or, check the status of all players – whether they are controlled by the computer or by a human. If all players except one are computers, then the mode is single-player. And rely on the fact that no one will launch a pseudo-single-player game through multiplayer (a hotseat game against only computer opponents).