[No QA] test: add a test for API.write() persistence ordering

tests/unit/APITest.ts

@@ -855,3 +855,59 @@ describe('APITests', () => {
             });
     });
 });
+
+// Issue: https://github.com/Expensify/App/issues/80759
+describe('API.write() persistence guarantees', () => {
+    // BUG: Currently, prepareRequest() applies optimistic data via Onyx.update() BEFORE
+    // processRequest() persists the request via SequentialQueue.push(). This test documents
+    // the buggy ordering. When the bug is fixed, flip the final assertion to toBe(true).
+    test('Issue 1: should persist the request before applying optimistic data', () =>
+        Onyx.multiSet({
+            [ONYXKEYS.CREDENTIALS]: {autoGeneratedLogin: 'test', autoGeneratedPassword: 'passwd'},
+            [ONYXKEYS.SESSION]: {authToken: 'testToken'},
+            [ONYXKEYS.NETWORK]: {isOffline: true},
+        }).then(() => {
+            let optimisticDataApplied = false;
+            let requestPersistedBeforeOptimistic = false;
+
+            // Mock Onyx.update so that when it receives our marker key we snapshot the
+            // persisted-requests queue. This avoids spy-ordering issues that caused
+            // false passes on CI.
+            const updateMock = jest.spyOn(Onyx, 'update').mockImplementation((data) => {
+                // We use ONYXKEYS.IS_CHECKING_PUBLIC_ROOM as a sample key to identify the marker
+                const hasMarker = data.some((entry) => entry.key === ONYXKEYS.IS_CHECKING_PUBLIC_ROOM);
+                if (hasMarker) {
+                    optimisticDataApplied = true;
+                    // Note: getAll() checks the in-memory queue, not durable (disk) state.
+                    // This is intentionally a weaker assertion – if even the in-memory
+                    // ordering is wrong (request not queued before optimistic data), the
+                    // stronger disk-persistence guarantee is certainly broken too.
+                    requestPersistedBeforeOptimistic = PersistedRequests.getAll().some((r) => r.command === 'MockCommand');
+                }
+                return Promise.resolve();
+            });
+
+            try {
+                API.write('MockCommand' as WriteCommand, {param1: 'value1'} as ApiRequestCommandParameters[WriteCommand], {
+                    optimisticData: [
+                        {
+                            onyxMethod: Onyx.METHOD.SET,
+                            key: ONYXKEYS.IS_CHECKING_PUBLIC_ROOM,
+                            value: true,
+                        },
+                    ],
+                });
+
+                // Guard: ensure our mock actually intercepted the optimistic data.
+                // Without this, the test could pass for the wrong reason (e.g. mock
+                // never fires, flag stays false, and we'd incorrectly confirm the bug).
+                expect(optimisticDataApplied).toBe(true);
+
+                // BUG: The request is NOT in the persisted queue when optimistic data is
+                // applied. When fixed, this assertion should be changed to toBe(true).
+                expect(requestPersistedBeforeOptimistic).toBe(false);
+            } finally {
+                updateMock.mockRestore();
+            }
+        }));
+});