diff --git a/.aios-core/core/execution/build-state-manager.js b/.aios-core/core/execution/build-state-manager.js
index a2ca4ad0c9..29a06e95c2 100644
--- a/.aios-core/core/execution/build-state-manager.js
+++ b/.aios-core/core/execution/build-state-manager.js
@@ -397,7 +397,7 @@ class BuildStateManager {
    * @returns {Object|null} Last checkpoint or null
    */
   getLastCheckpoint() {
-    if (!this._state || this._state.checkpoints.length === 0) {
+    if (!this._state || !this._state.checkpoints || this._state.checkpoints.length === 0) {
       return null;
     }
     return this._state.checkpoints[this._state.checkpoints.length - 1];
@@ -410,7 +410,7 @@ class BuildStateManager {
    * @returns {Object|null} Checkpoint or null
    */
   getCheckpoint(checkpointId) {
-    if (!this._state) {
+    if (!this._state || !this._state.checkpoints) {
       return null;
     }
     return this._state.checkpoints.find((c) => c.id === checkpointId) || null;
@@ -551,11 +551,11 @@ class BuildStateManager {
             : 0,
       },
       metrics: state.metrics,
-      recentFailures: state.failedAttempts.slice(-5),
+      recentFailures: (state.failedAttempts || []).slice(-5),
       abandoned: isAbandoned,
       worktree: state.worktree,
-      checkpointCount: state.checkpoints.length,
-      notificationCount: state.notifications.filter((n) => !n.acknowledged).length,
+      checkpointCount: (state.checkpoints || []).length,
+      notificationCount: (state.notifications || []).filter((n) => !n.acknowledged).length,
     };
   }
 
@@ -781,6 +781,8 @@ class BuildStateManager {
       throw new Error('No state loaded');
     }
 
+    this._state.failedAttempts ??= [];
+
     const failure = {
       subtaskId,
       attempt:
@@ -831,7 +833,7 @@ class BuildStateManager {
     }
 
     // Get attempts for this subtask
-    const attempts = this._state.failedAttempts
+    const attempts = (this._state.failedAttempts || [])
       .filter((f) => f.subtaskId === subtaskId)
       .map((f) => ({
         success: false,
@@ -895,7 +897,7 @@ class BuildStateManager {
    */
   getNotifications() {
     if (!this._state) return [];
-    return this._state.notifications.filter((n) => !n.acknowledged);
+    return (this._state.notifications || []).filter((n) => !n.acknowledged);
   }
 
   /**
@@ -904,7 +906,7 @@ class BuildStateManager {
    * @param {number} index - Notification index
    */
   acknowledgeNotification(index) {
-    if (!this._state || !this._state.notifications[index]) return;
+    if (!this._state || !this._state.notifications || !this._state.notifications[index]) return;
     this._state.notifications[index].acknowledged = true;
     this.saveState();
   }
diff --git a/tests/core/execution/build-state-manager-guards.test.js b/tests/core/execution/build-state-manager-guards.test.js
new file mode 100644
index 0000000000..6b3be28ce0
--- /dev/null
+++ b/tests/core/execution/build-state-manager-guards.test.js
@@ -0,0 +1,239 @@
+/**
+ * Testes para null guards em BuildStateManager
+ *
+ * Valida que getLastCheckpoint, getCheckpoint, getStatus,
+ * getNotifications, acknowledgeNotification e recordFailure
+ * não falham com TypeError quando arrays são undefined.
+ *
+ * Closes #513
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+// Mock fs para evitar I/O real
+jest.spyOn(fs, 'existsSync').mockReturnValue(false);
+jest.spyOn(fs, 'mkdirSync').mockImplementation(() => {});
+
+const { BuildStateManager } = require('../../../.aios-core/core/execution/build-state-manager');
+
+describe('BuildStateManager - null guards (#513)', () => {
+  let manager;
+
+  beforeEach(() => {
+    manager = new BuildStateManager('test-story', {
+      rootPath: '/fake/project',
+    });
+  });
+
+  // ============================================================
+  // getLastCheckpoint
+  // ============================================================
+  describe('getLastCheckpoint', () => {
+    test('retorna null quando _state é null', () => {
+      manager._state = null;
+      expect(manager.getLastCheckpoint()).toBeNull();
+    });
+
+    test('retorna null quando checkpoints é undefined', () => {
+      manager._state = { status: 'running' };
+      expect(manager.getLastCheckpoint()).toBeNull();
+    });
+
+    test('retorna null quando checkpoints é array vazio', () => {
+      manager._state = { checkpoints: [] };
+      expect(manager.getLastCheckpoint()).toBeNull();
+    });
+
+    test('retorna último checkpoint', () => {
+      const checkpoint = { id: 'cp-2', phase: 'build' };
+      manager._state = {
+        checkpoints: [{ id: 'cp-1', phase: 'setup' }, checkpoint],
+      };
+      expect(manager.getLastCheckpoint()).toEqual(checkpoint);
+    });
+  });
+
+  // ============================================================
+  // getCheckpoint
+  // ============================================================
+  describe('getCheckpoint', () => {
+    test('retorna null quando _state é null', () => {
+      manager._state = null;
+      expect(manager.getCheckpoint('cp-1')).toBeNull();
+    });
+
+    test('retorna null quando checkpoints é undefined', () => {
+      manager._state = { status: 'running' };
+      expect(manager.getCheckpoint('cp-1')).toBeNull();
+    });
+
+    test('retorna null quando checkpoint não existe', () => {
+      manager._state = { checkpoints: [{ id: 'cp-1' }] };
+      expect(manager.getCheckpoint('cp-999')).toBeNull();
+    });
+
+    test('retorna checkpoint pelo ID', () => {
+      const target = { id: 'cp-2', phase: 'test' };
+      manager._state = {
+        checkpoints: [{ id: 'cp-1' }, target],
+      };
+      expect(manager.getCheckpoint('cp-2')).toEqual(target);
+    });
+  });
+
+  // ============================================================
+  // constructor
+  // ============================================================
+  describe('constructor', () => {
+    test('requer storyId', () => {
+      expect(() => new BuildStateManager()).toThrow('storyId is required');
+    });
+
+    test('aceita storyId string', () => {
+      const m = new BuildStateManager('story-123');
+      expect(m.storyId).toBe('story-123');
+    });
+
+    test('inicializa _state como null', () => {
+      expect(manager._state).toBeNull();
+    });
+
+    test('usa rootPath padrão se não fornecido', () => {
+      const m = new BuildStateManager('s1');
+      expect(m.rootPath).toBe(process.cwd());
+    });
+  });
+
+  // ============================================================
+  // getStatus - null guards para arrays opcionais
+  // ============================================================
+  describe('getStatus', () => {
+    test('retorna exists:false quando loadState retorna null', () => {
+      jest.spyOn(manager, 'loadState').mockReturnValue(null);
+      const status = manager.getStatus();
+      expect(status.exists).toBe(false);
+    });
+
+    test('calcula recentFailures com failedAttempts undefined', () => {
+      jest.spyOn(manager, 'loadState').mockReturnValue({
+        status: 'running',
+        startedAt: new Date().toISOString(),
+        currentPhase: 'build',
+        currentSubtask: null,
+        metrics: { completedSubtasks: 0, totalSubtasks: 1, totalFailures: 0, totalAttempts: 0 },
+        worktree: null,
+        lastCheckpoint: null,
+      });
+      jest.spyOn(manager, '_checkAbandoned').mockReturnValue(false);
+      const status = manager.getStatus();
+      expect(status.recentFailures).toEqual([]);
+      expect(status.checkpointCount).toBe(0);
+      expect(status.notificationCount).toBe(0);
+    });
+
+    test('calcula checkpointCount e notificationCount com arrays presentes', () => {
+      jest.spyOn(manager, 'loadState').mockReturnValue({
+        status: 'running',
+        startedAt: new Date().toISOString(),
+        currentPhase: 'build',
+        currentSubtask: null,
+        metrics: { completedSubtasks: 0, totalSubtasks: 1, totalFailures: 0, totalAttempts: 0 },
+        worktree: null,
+        lastCheckpoint: null,
+        checkpoints: [{ id: 'cp-1' }, { id: 'cp-2' }],
+        notifications: [
+          { acknowledged: false },
+          { acknowledged: true },
+          { acknowledged: false },
+        ],
+        failedAttempts: [{ subtaskId: 'a' }, { subtaskId: 'b' }],
+      });
+      jest.spyOn(manager, '_checkAbandoned').mockReturnValue(false);
+      const status = manager.getStatus();
+      expect(status.checkpointCount).toBe(2);
+      expect(status.notificationCount).toBe(2);
+      expect(status.recentFailures).toHaveLength(2);
+    });
+  });
+
+  // ============================================================
+  // getNotifications - null guard
+  // ============================================================
+  describe('getNotifications', () => {
+    test('retorna array vazio quando _state é null', () => {
+      manager._state = null;
+      expect(manager.getNotifications()).toEqual([]);
+    });
+
+    test('retorna array vazio quando notifications é undefined', () => {
+      manager._state = { status: 'running' };
+      expect(manager.getNotifications()).toEqual([]);
+    });
+
+    test('filtra apenas não-acknowledged', () => {
+      manager._state = {
+        notifications: [
+          { message: 'a', acknowledged: false },
+          { message: 'b', acknowledged: true },
+          { message: 'c', acknowledged: false },
+        ],
+      };
+      const result = manager.getNotifications();
+      expect(result).toHaveLength(2);
+      expect(result[0].message).toBe('a');
+      expect(result[1].message).toBe('c');
+    });
+  });
+
+  // ============================================================
+  // acknowledgeNotification - null guard
+  // ============================================================
+  describe('acknowledgeNotification', () => {
+    test('não falha quando _state é null', () => {
+      manager._state = null;
+      expect(() => manager.acknowledgeNotification(0)).not.toThrow();
+    });
+
+    test('não falha quando notifications é undefined', () => {
+      manager._state = { status: 'running' };
+      expect(() => manager.acknowledgeNotification(0)).not.toThrow();
+    });
+
+    test('não falha com índice inválido', () => {
+      manager._state = { notifications: [{ acknowledged: false }] };
+      jest.spyOn(manager, 'saveState').mockImplementation(() => {});
+      expect(() => manager.acknowledgeNotification(99)).not.toThrow();
+    });
+
+    test('marca notification como acknowledged', () => {
+      manager._state = {
+        notifications: [
+          { message: 'alerta', acknowledged: false },
+        ],
+      };
+      jest.spyOn(manager, 'saveState').mockImplementation(() => {});
+      manager.acknowledgeNotification(0);
+      expect(manager._state.notifications[0].acknowledged).toBe(true);
+    });
+  });
+
+  // ============================================================
+  // recordFailure - failedAttempts null guard
+  // ============================================================
+  describe('recordFailure', () => {
+    test('inicializa failedAttempts quando undefined', () => {
+      manager._state = {
+        status: 'running',
+        metrics: { totalFailures: 0, totalAttempts: 0 },
+        notifications: [],
+      };
+      jest.spyOn(manager, 'saveState').mockImplementation(() => {});
+      jest.spyOn(manager, '_logAttempt').mockImplementation(() => {});
+
+      const result = manager.recordFailure('subtask-1', { error: 'test error' });
+      expect(result.failure.subtaskId).toBe('subtask-1');
+      expect(manager._state.failedAttempts).toHaveLength(1);
+    });
+  });
+});