I've got my own interpretation of all this.Here are my working definitions of terminal and non-terminal:
- Terminal Action - A card that, when played, decreases the number of additional terminal actions you can play on the same turn.
- Non-Terminal Action - A card that, when played, does not decrease the number of additional terminal actions you can play on the same turn.
Action splitters( or "villages") are a subset of non-terminal actions.
- Action Splitter - A card that, when played, increases the number of additional terminal actions you can play on the same turn.
You kinda have to add a special rule to the game that stipulates "When you cannot play any additional actions on your turn, you cannot play any additional non-terminals on that turn either". Notice the emphasis on the current turn. I'll explain why I define them like that shortly.
What are the consequences of these definitions? Well, all existing cantrips and cards that give +1 action are clearly non-terminal. What's key is that the number of non-terminals you can have in play is unbounded by the number of actions available, assuming the available number of actions is not zero.
Also, KC/TR/Golem/etc. are not only non-terminal, but action splitters as well. For example, playing one TR lets me play at least two additional terminal actions. An unbounded chain of them can play an unbounded number of terminals. I mean, a hypothetical hand of 50 Throne Rooms and 50 Militias can have all 50 Militias played and then some.
The big point I wanted to discuss is what durations fit into the "Terminal" category. By my definition Wharf, Tactician, and Merchant Ship are terminal, but Fishing Village and Caravan are non-terminals.
A hypothetical card that had an effect like "+1 action. At the start of your next turn, -1 action" would actually be non-terminal. Why? Because on the turn you play that hypothetical card, you can play as many other copies of it as possible, as well as any number of other non-terminals as well. Admittedly, my definition breaks down when the Tactician effect is considered (-1 action now, +2 actions next turn).
In theory, a delayed village (-1 action now, +2 actions next turn) can have two more copies of the delayed village played next turn, which can in turn lead to another 4 copies of the delayed village being played the turn after. At least, that doesn't happen with Tactician due to the hand discarding that can only be overcome with specific action splitters (Herald, Golem). But Wharf? Without action splitters, you can only have at most 2 copies of them in play at one time (one will have had to been played last the turn, the other in the current turn). Compare that to, say, Market that can have an unbounded number of them in play at once. The difference between infinity to 1 (The case for most terminals) and infinity to 2 (Durations like Wharf and Merchant Ship) is virtually nothing. It's also impossible to put into play 2 Wharves on the same turn, because there is no way to put Wharf in play in the first place without losing an available action first.
The notion of "half-terminal" doesn't have much theoretical significance, although when put to practical analysis it means you can reduce the number of terminal collisions with half-terminals. I also feel like introducing the notion of "half non-terminal", for any hypothetical card that says something like "set aside a copy of this card from your hand. If you do, +1 action. Discard the cards set aside this way during clean-up". The closest we have to a card like that is Nobles.
tl,dr: I say KC/TR/Golem/etc. are non-terminal, and are even action splitters. Wharf is terminal. Tactician is effectively terminal due to the discard-the-hand thing, but would otherwise be non-terminal.
Edit: Formatting