fix(reports): fail report on tiled screenshot error instead of sending blank PDF

When take_tiled_screenshot returns None, the previous fallback immediately took
a standard element.screenshot() with no spinner check or animation wait, which
produced a blank image that silently became a blank PDF sent to recipients.

Remove the fallback: return None instead, which propagates up through
_get_screenshots() → ReportScheduleScreenshotFailedError → ERROR execution
state with owner notification.

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

superset/utils/webdriver.py

@@ -375,15 +375,12 @@ class WebDriverPlaywright(WebDriverProxy):
                             animation_wait=selenium_animation_wait,
                         )
                         if img is None:
-                            logger.warning(
-                                (
-                                    "Tiled screenshot failed, "
-                                    "falling back to standard screenshot"
-                                )
-                            )
-                            img = WebDriverPlaywright._get_screenshot(
-                                page, element, element_name
+                            logger.error(
+                                "Tiled screenshot failed at url %s; "
+                                "not falling back to avoid sending a blank PDF",
+                                url,
                             )
+                            return None
                     else:
                         # Standard screenshot captures the full element including
                         # below-the-fold content, so wait for all spinners globally.

tests/unit_tests/utils/webdriver_test.py

@@ -898,3 +898,76 @@ class TestWebDriverPlaywrightErrorHandling:
             "dashboard",
             "http://example.com",
         )
+
+    @patch("superset.utils.webdriver.PLAYWRIGHT_AVAILABLE", True)
+    @patch("superset.utils.webdriver.sync_playwright")
+    @patch("superset.utils.webdriver.logger")
+    @patch("superset.utils.webdriver.take_tiled_screenshot")
+    def test_tiled_screenshot_failure_returns_none_without_fallback(
+        self, mock_take_tiled, mock_logger, mock_sync_playwright
+    ):
+        """When take_tiled_screenshot fails, return None rather than fall back to a
+        potentially blank standard screenshot."""
+        mock_user = MagicMock()
+        mock_user.username = "test_user"
+
+        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.wait_for.return_value = None
+        mock_element.screenshot.return_value = b"should_not_be_called"
+
+        def evaluate_side_effect(script):
+            if "querySelectorAll" in script:
+                return 25  # chart_count >= threshold
+            if "const target" in script:
+                return 6000  # dashboard_height > height_threshold and > tile_height
+            return None
+
+        mock_page.evaluate.side_effect = evaluate_side_effect
+        mock_take_tiled.return_value = None  # tiled screenshot fails
+
+        with patch("superset.utils.webdriver.app") as mock_app:
+            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_LOCATE_WAIT": 10,
+                "SCREENSHOT_LOAD_WAIT": 10,
+                "SCREENSHOT_WAIT_FOR_ERROR_MODAL_VISIBLE": 10,
+                "SCREENSHOT_WAIT_FOR_ERROR_MODAL_INVISIBLE": 10,
+                "SCREENSHOT_REPLACE_UNEXPECTED_ERRORS": False,
+                "SCREENSHOT_TILED_ENABLED": True,
+                "SCREENSHOT_TILED_CHART_THRESHOLD": 20,
+                "SCREENSHOT_TILED_HEIGHT_THRESHOLD": 5000,
+                "SCREENSHOT_TILED_VIEWPORT_HEIGHT": 600,
+            }
+
+            with patch.object(WebDriverPlaywright, "auth") as mock_auth:
+                mock_auth.return_value = mock_context
+
+                driver = WebDriverPlaywright("chrome")
+                result = driver.get_screenshot(
+                    "http://example.com", "dashboard", mock_user
+                )
+
+        assert result is None
+        mock_element.screenshot.assert_not_called()
+        mock_logger.error.assert_any_call(
+            "Tiled screenshot failed at url %s; "
+            "not falling back to avoid sending a blank PDF",
+            "http://example.com",
+        )