feat(heartbeat): add process memory and backup health checks

src/backup/status.test.ts

@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'vitest';
+import {
+  getBackupHealthSnapshot,
+  initBackupHealth,
+  markBackupFailure,
+  markBackupSuccess,
+} from './status.js';
+
+describe('backup status tracker', () => {
+  it('tracks failures and resets on success', () => {
+    initBackupHealth(true);
+    expect(getBackupHealthSnapshot()).toMatchObject({
+      enabled: true,
+      hasRun: false,
+      consecutiveFailures: 0,
+    });
+
+    markBackupFailure('upload failed', 123);
+    expect(getBackupHealthSnapshot()).toMatchObject({
+      enabled: true,
+      hasRun: true,
+      consecutiveFailures: 1,
+      lastFailureAt: 123,
+      lastError: 'upload failed',
+    });
+
+    markBackupFailure('upload failed again', 456);
+    expect(getBackupHealthSnapshot()).toMatchObject({
+      consecutiveFailures: 2,
+      lastFailureAt: 456,
+      lastError: 'upload failed again',
+    });
+
+    markBackupSuccess(789);
+    expect(getBackupHealthSnapshot()).toMatchObject({
+      hasRun: true,
+      consecutiveFailures: 0,
+      lastSuccessAt: 789,
+      lastError: undefined,
+    });
+  });
+});