Villager Connect Four

That Master-level librarian drives a hard bargain. They have also solved Connect Four, and they are going first.

Open any villager's trade screen and hit Connect Four. A full board opens right there - no items, no commands, no setup.

The villager goes first, and that is the point

Connect Four is a solved game. On the standard 7×6 board the player who drops first can force a win - that is a proved result, not a rule of thumb. Whoever moves first is playing a won game.

So the villager gets it. A Master villager isn't "very strong": it is unbeatable. If you would rather have the winning side, one line of config hands it to you. Your colour follows the turn order, so whoever drops first plays yellow.

How strong are they?

A villager's trading level sets its strength, and each level thinks in a genuinely different way rather than just deeper:

Villager level	Connect Four strength
Novice	Drops almost at random - won't take a win, won't block yours
Apprentice	Takes the win in front of it, blocks yours, sees nothing further
Journeyman	Never plays into a loss; makes and spots double threats
Expert	Understands odd/even threat parity
Master	Has solved the game

The Journeyman-to-Expert step is the interesting one. Every column holds an even number of cells, so in a pure filling race the first player takes the 1st, 3rd and 5th cell of a column and the second takes the 2nd, 4th and 6th. A threat only pays off if its row falls to its owner - the same three-in-a-row one row higher can be worth nothing at all. A Journeyman counts threats; an Expert counts the ones that will actually be reached.

How to play

Click a column, or anywhere above it. A ghost disc hangs over the column you are pointing at.
A full column flashes red with a dull note rather than quietly ignoring you.
The winning four are outlined and the rest of the board dims.
Resign with the button, or just close the board. Walking more than 16 blocks away, the villager dying, or disconnecting abandons the game.
No stakes, no rewards - just for fun.

Configuration

config/villagerconnectfour.properties, written on first run and documented inline:

first-player=player - you drop first, and get the theoretically winning side.
board-size=7x6 - anything from 4x4 to 8x7. This changes the value of the game, not just its scale: several smaller boards are draws with perfect play.

Under the hood

A from-scratch pure-Java engine. The board is two bitboards in a single 64-bit word, one column per seven bits; the spare bit per column is a sentinel that stays empty, which is what lets four-in-a-row be found by and-ing the board with shifted copies of itself with no edge checks.
Scores are counted in discs on the board rather than plies from the search root, so they are absolute facts about a position. One transposition table is shared by every game on the server, and a Master's knowledge compounds through a game rather than starting cold each move.
Fully server-authoritative - the client sends a column and nothing else.
The engine thinks on a background thread, so the server never stalls.
Zero art: board, discs, holes and highlights are drawn procedurally and stay crisp at any size.

Compatibility

Plays nicely with the other Villager Games mods - the trade-screen buttons stack instead of overlapping.

Requires Fabric API. Client and server both need the mod.

Requirements

Minecraft 26.2
Fabric Loader 0.19.3+ and Fabric API
Java 25
Install on both client and server (works in singleplayer out of the box)