chore: import upstream snapshot with attribution

apps/sim/lib/data-drains/sources/cursor.test.ts

@@ -0,0 +1,26 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it } from 'vitest'
+import { decodeTimeCursor, encodeTimeCursor } from '@/lib/data-drains/sources/cursor'
+
+describe('time cursor encoding', () => {
+  it('round-trips a valid cursor', () => {
+    const value = { ts: '2026-01-01T00:00:00.000Z', id: 'row-1' }
+    expect(decodeTimeCursor(encodeTimeCursor(value))).toEqual(value)
+  })
+
+  it('returns null for null input', () => {
+    expect(decodeTimeCursor(null)).toBeNull()
+  })
+
+  it('returns null for malformed JSON', () => {
+    expect(decodeTimeCursor('not-json')).toBeNull()
+  })
+
+  it('returns null when shape is wrong', () => {
+    expect(decodeTimeCursor(JSON.stringify({ ts: 1, id: 'x' }))).toBeNull()
+    expect(decodeTimeCursor(JSON.stringify({ ts: '2026', id: 5 }))).toBeNull()
+    expect(decodeTimeCursor(JSON.stringify({}))).toBeNull()
+  })
+})