UCI: stop FEN parsing at the "moves" keyword

ChessKit/Sources/ChessProtocol/UCI.swift

@@ -69,7 +69,7 @@ public final class UCIEngine {
 
     // MARK: - Command handlers
 
-    /// Parses `position [startpos | fen <6 fields>] [moves <uci>...]`.
+    /// Parses `position [startpos | fen <fen fields>] [moves <uci>...]`.
     private func applyPosition(_ args: [String]) {
         var index = 0
         var newBoard: Board?
@@ -78,8 +78,11 @@ public final class UCIEngine {
             newBoard = Board()
             index = 1
         } else if args.first == "fen" {
-            // A FEN is up to six space-separated fields following "fen".
-            let fenFields = Array(args.dropFirst().prefix(6))
+            // The FEN runs until the "moves" keyword, capped at six fields.
+            // Stopping at "moves" is what lets a short FEN (Board accepts 4–5
+            // fields, defaulting the clocks) keep its trailing moves instead of
+            // swallowing the "moves" token and the moves into the FEN string.
+            let fenFields = Array(args.dropFirst().prefix { $0 != "moves" }.prefix(6))
             newBoard = Board(fen: fenFields.joined(separator: " "))
             index = 1 + fenFields.count
         }

ChessKit/Tests/ChessProtocolTests/UCITests.swift

@@ -42,6 +42,16 @@ final class UCITests: XCTestCase {
         XCTAssertNil(uci.currentBoard[Sq.parse("e2")!])
     }
 
+    func testPositionShortFENWithMoves() {
+        // A 4-field FEN (no halfmove/fullmove counters) followed by moves.
+        // The "moves" keyword must not be absorbed into the FEN, or the move
+        // is silently dropped and e2e4 is never applied.
+        let uci = makeAdapter()
+        uci.process("position fen 4k3/8/8/8/8/8/4P3/4K3 w - - moves e2e4")
+        XCTAssertEqual(uci.currentBoard[Sq.parse("e4")!], Piece(color: .white, kind: .pawn))
+        XCTAssertNil(uci.currentBoard[Sq.parse("e2")!])
+    }
+
     func testUCINewGameResets() {
         let uci = makeAdapter()
         uci.process("position startpos moves e2e4")