feat: add Session and stage active check

packages/game/test/stage.test.ts

@@ -2,6 +2,7 @@ import { test, expect } from '@jest/globals'
 import { Stage } from '../src/Stage'
 import { FileType } from '../src/types'
 import { MockFileChecker } from './asyncCondition.test'
+import { Session } from '../src/Session'
 
 const checker = new MockFileChecker()
 
@@ -67,3 +68,21 @@ test('check stage with async condition falsy', async () => {
   })
   expect(await stage.satisfies({}, checker)).toBe(false)
 })
+
+test('stage active checks', () => {
+  const session = new Session({
+    completedStages: ['stage1'],
+  })
+  const stage3 = new Stage({
+    id: 'stage3',
+    requirements: ['stage1', 'stage2'],
+    condition: {},
+  })
+  expect(stage3.active(session)).toBe(false)
+
+  session.complete('stage2')
+  expect(stage3.active(session)).toBe(true)
+
+  session.complete('stage3')
+  expect(stage3.active(session)).toBe(false)
+})