Are there any in-game restrictions on playing the trapped! and the tool-breaking cards in the end of the round? For example, can I play the trapped card as my last one on a player who has no more cards?
In the rules there are no special restrictions for the new action cards.
In the normal gameplay:
When it is your turn, you have to take one of the four following actions:
- Place a path card in the tunnel maze then draw 1 card.
- Play an action card then draw 1 card.
- Discard two cards from your hand to remove a card in front of you then draw 1 card.
- Pass and discard 1-3 face-down cards from your hand then draw 1-3 cards.
Then your turn is over and it's the next player's turn.
There is also no restriction mentioned for the trapped card:
Trapped! (3 in the game)
Play this card face-up in front of another player of your choice. This player is trapped and cannot play any more path cards. If a player is trapped when the round ends, they don't get counted as one of the winners and don't get a cut of the treasure.
So yes you can play an trapped card on a player that has no cards in hand. It literally traps the player, but he or she can be rescued by another player using the "Free at last!" card.