The checkmate scene has one mate: a Scarlet Thief watches d1, so the Oliphant that goes there gives check and dies for it

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CCLa2PaEeCj8njQZSWGqHx

src/lib/game/lessons.test.ts

@@ -52,10 +52,19 @@ describe('the lessons', () => {
 		const king = sceneCells(at('king'));
 		expect(inCheck(king, 'gold')).toBe(true);
 		expect(legalMovesFrom(king, square('2g1'), 'printed').map((i) => i).sort()).toEqual([square('1g1'), square('2f1'), square('2h1'), square('3g1')].sort());
-		// The last scene is mate in one, and only that move mates.
+		// The last scene is mate in one by either listed move, and by no other.
 		const mate = play('mate');
-		expect(inCheck(mate.after.cells, 'scarlet')).toBe(true);
-		expect(hasLegalMove(mate.after.cells, 'scarlet', 'printed')).toBe(false);
+		for (const [from, to] of mate.s.moves) {
+			const after = playOn(mate.cells, square(from), square(to)).cells;
+			expect(inCheck(after, 'scarlet'), `${from} to ${to}`).toBe(true);
+			expect(hasLegalMove(after, 'scarlet', 'printed'), `${from} to ${to}`).toBe(false);
+		}
+		const listed = new Set(mate.s.moves.map(([a, b]) => `${square(a)}-${square(b)}`));
+		for (const to of legalMovesFrom(mate.cells, square('2a1'), 'printed')) {
+			if (listed.has(`${square('2a1')}-${to}`)) continue;
+			const after = playOn(mate.cells, square('2a1'), to).cells;
+			expect(inCheck(after, 'scarlet') && !hasLegalMove(after, 'scarlet', 'printed'), `unlisted mate by the Oliphant to ${to}`).toBe(false);
+		}
 		expect(kindOf(mate.cells[square('2d4')])).toBe('K');
 		expect(frozen(mate.cells, square('2d4'))).toBe(true);
 		void other;