refactor: add some part management utilities

tests/samples/tic-tac-toe.test.ts

@@ -163,9 +163,9 @@ describe('TicTacToe - helper functions', () => {
             const state = getState(ctx);
             placePiece(state, 1, 1, 'X');
 
-            expect(Object.keys(state.value.parts).length).toBe(1);
-            expect(state.value.parts['piece-X-1'].position).toEqual([1, 1]);
-            expect(state.value.parts['piece-X-1'].player).toBe('X');
+            expect(state.value.parts.length).toBe(1);
+            expect(state.value.parts.find(p => p.id === 'piece-X-1')!.position).toEqual([1, 1]);
+            expect(state.value.parts.find(p => p.id === 'piece-X-1')!.player).toBe('X');
         });
 
         it('should add piece to board region children', () => {
@@ -183,7 +183,7 @@ describe('TicTacToe - helper functions', () => {
             placePiece(state, 0, 0, 'X');
             placePiece(state, 0, 1, 'O');
 
-            const ids = Object.keys(state.value.parts);
+            const ids = state.value.parts.map(p => p.id);
             expect(new Set(ids).size).toBe(2);
         });
     });
@@ -229,8 +229,8 @@ describe('TicTacToe - game flow', () => {
         const result = await runPromise;
         expect(result.success).toBe(true);
         if (result.success) expect(result.result.winner).toBeNull();
-        expect(Object.keys(ctx.state.value.parts).length).toBe(1);
-        expect(ctx.state.value.parts['piece-X-1'].position).toEqual([1, 1]);
+        expect(ctx.state.value.parts.length).toBe(1);
+        expect(ctx.state.value.parts.find(p => p.id === 'piece-X-1')!.position).toEqual([1, 1]);
     });
 
     it('should reject move for wrong player and re-prompt', async () => {