fix: 优化收款码加载态，避免首屏错误占位闪现

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkanTests/PaymentCollectionDetailsViewModelTests.swift

@@ -69,6 +69,26 @@ final class PaymentCollectionDetailsViewModelTests: XCTestCase {
         XCTAssertFalse(viewModel.showAmountDialog)
     }
 
+    func testPayCodeLoadingStateCoversInitialRenderAndRequest() async {
+        let payCodeJSON = """
+        {"code":100000,"msg":"success","data":{"static_pay_url":"https://pay.example.com/static","dynamic_pay_url":"https://pay.example.com/dynamic"}}
+        """.data(using: .utf8)!
+        let session = MockURLSession(responses: [payCodeJSON])
+        let api = PaymentAPI(client: APIClient(environment: .testing, session: session))
+        let viewModel = PaymentCollectionDetailsViewModel(appStore: appStore)
+        var loadingStates = [viewModel.isPayCodeLoading]
+        viewModel.onStateChange = {
+            loadingStates.append(viewModel.isPayCodeLoading)
+        }
+
+        await viewModel.loadPayCode(api: api)
+
+        XCTAssertEqual(loadingStates.first, true)
+        XCTAssertTrue(loadingStates.dropLast().allSatisfy { $0 })
+        XCTAssertEqual(loadingStates.last, false)
+        XCTAssertTrue(viewModel.hasPayCode)
+    }
+
     func testToggleReceiveVoicePersistsInAppStore() {
         let viewModel = PaymentCollectionDetailsViewModel(appStore: appStore)
         viewModel.refreshLocalState()
@@ -105,6 +125,7 @@ final class PaymentCollectionDetailsViewModelTests: XCTestCase {
 
         await viewModel.loadPayCode(api: api)
 
+        XCTAssertFalse(viewModel.isPayCodeLoading)
         XCTAssertFalse(viewModel.hasPayCode)
         XCTAssertEqual(session.requests.count, 0)
     }