fix(reports): poll for spinner absence instead of snapshotting loading elements

The Playwright screenshot path waited for `.loading` elements to detach
by calling `page.locator(".loading").all()` once and iterating the
snapshot. Spinners that appeared after the snapshot was taken (common on
long dashboards where charts load lazily) were never waited for, causing
PDF reports to capture charts that were still fetching data.

Replace the snapshot loop with `page.wait_for_function` which
continuously polls `document.querySelectorAll('.loading').length === 0`
until the page is genuinely clear of all spinners, then use
`self._screenshot_load_wait` (already stored on the base class) for the
timeout to stay consistent with the Selenium path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit_tests/utils/webdriver_test.py

@@ -640,6 +640,114 @@ class TestWebDriverPlaywrightErrorHandling:
         mock_button.click.assert_called_once()
         mock_close_button.click.assert_called_once()
 
+    @patch("superset.utils.webdriver.PLAYWRIGHT_AVAILABLE", True)
+    @patch("superset.utils.webdriver.sync_playwright")
+    @patch("superset.utils.webdriver.app")
+    def test_uses_wait_for_function_to_detect_spinners(
+        self, mock_app, mock_sync_playwright
+    ):
+        """wait_for_function polls for spinner absence rather than snapshotting."""
+        mock_user = MagicMock()
+        mock_user.username = "test_user"
+        mock_app.config = {
+            "WEBDRIVER_OPTION_ARGS": [],
+            "WEBDRIVER_WINDOW": {"pixel_density": 1},
+            "SCREENSHOT_PLAYWRIGHT_DEFAULT_TIMEOUT": 30000,
+            "SCREENSHOT_PLAYWRIGHT_WAIT_EVENT": "networkidle",
+            "SCREENSHOT_SELENIUM_HEADSTART": 0,
+            "SCREENSHOT_SELENIUM_ANIMATION_WAIT": 0,
+            "SCREENSHOT_REPLACE_UNEXPECTED_ERRORS": False,
+            "SCREENSHOT_TILED_ENABLED": False,
+            "SCREENSHOT_LOCATE_WAIT": 10,
+            "SCREENSHOT_LOAD_WAIT": 60,
+            "SCREENSHOT_WAIT_FOR_ERROR_MODAL_VISIBLE": 10,
+            "SCREENSHOT_WAIT_FOR_ERROR_MODAL_INVISIBLE": 10,
+        }
+
+        mock_playwright_instance = MagicMock()
+        mock_browser = MagicMock()
+        mock_context = MagicMock()
+        mock_page = MagicMock()
+        mock_element = MagicMock()
+
+        mock_sync_playwright.return_value.__enter__.return_value = (
+            mock_playwright_instance
+        )
+        mock_playwright_instance.chromium.launch.return_value = mock_browser
+        mock_browser.new_context.return_value = mock_context
+        mock_context.new_page.return_value = mock_page
+        mock_page.locator.return_value = mock_element
+        mock_element.screenshot.return_value = b"screenshot"
+
+        with patch.object(WebDriverPlaywright, "auth", return_value=mock_context):
+            driver = WebDriverPlaywright("chrome")
+            driver.get_screenshot("http://example.com", "test-element", mock_user)
+
+        mock_page.wait_for_function.assert_called_once_with(
+            "() => document.querySelectorAll('.loading').length === 0",
+            timeout=60 * 1000,
+        )
+        # Guard against reintroducing the old snapshot-based approach
+        loading_locator_calls = [
+            c for c in mock_page.locator.call_args_list if c.args == (".loading",)
+        ]
+        assert loading_locator_calls == []
+
+    @patch("superset.utils.webdriver.PLAYWRIGHT_AVAILABLE", True)
+    @patch("superset.utils.webdriver.sync_playwright")
+    @patch("superset.utils.webdriver.logger")
+    @patch("superset.utils.webdriver.app")
+    def test_spinner_timeout_logs_warning_and_raises(
+        self, mock_app, mock_logger, mock_sync_playwright
+    ):
+        """Spinner timeout is logged as a warning and re-raised."""
+        from superset.utils.webdriver import PlaywrightTimeout
+
+        mock_user = MagicMock()
+        mock_user.username = "test_user"
+        mock_app.config = {
+            "WEBDRIVER_OPTION_ARGS": [],
+            "WEBDRIVER_WINDOW": {"pixel_density": 1},
+            "SCREENSHOT_PLAYWRIGHT_DEFAULT_TIMEOUT": 30000,
+            "SCREENSHOT_PLAYWRIGHT_WAIT_EVENT": "networkidle",
+            "SCREENSHOT_SELENIUM_HEADSTART": 0,
+            "SCREENSHOT_SELENIUM_ANIMATION_WAIT": 0,
+            "SCREENSHOT_REPLACE_UNEXPECTED_ERRORS": False,
+            "SCREENSHOT_TILED_ENABLED": False,
+            "SCREENSHOT_LOCATE_WAIT": 10,
+            "SCREENSHOT_LOAD_WAIT": 60,
+            "SCREENSHOT_WAIT_FOR_ERROR_MODAL_VISIBLE": 10,
+            "SCREENSHOT_WAIT_FOR_ERROR_MODAL_INVISIBLE": 10,
+        }
+
+        mock_playwright_instance = MagicMock()
+        mock_browser = MagicMock()
+        mock_context = MagicMock()
+        mock_page = MagicMock()
+        mock_element = MagicMock()
+
+        mock_sync_playwright.return_value.__enter__.return_value = (
+            mock_playwright_instance
+        )
+        mock_playwright_instance.chromium.launch.return_value = mock_browser
+        mock_browser.new_context.return_value = mock_context
+        mock_context.new_page.return_value = mock_page
+        mock_page.locator.return_value = mock_element
+
+        timeout = PlaywrightTimeout()
+        mock_page.wait_for_function.side_effect = timeout
+
+        with patch.object(WebDriverPlaywright, "auth", return_value=mock_context):
+            driver = WebDriverPlaywright("chrome")
+            with pytest.raises(PlaywrightTimeout) as exc_info:
+                driver.get_screenshot("http://example.com", "test-element", mock_user)
+
+        assert exc_info.value is timeout
+        mock_logger.warning.assert_any_call(
+            "Timed out waiting for charts to load at url %s",
+            "http://example.com",
+        )
+
     @patch("superset.utils.webdriver.PLAYWRIGHT_AVAILABLE", True)
     @patch("superset.utils.webdriver.sync_playwright")
     @patch("superset.utils.webdriver.logger")