fix(reports): fail closed on alert screenshot capture instead of delivering a blank

[eschutho]

SUMMARY

Scheduled alerts that attach a dashboard/chart screenshot (PNG/PDF) could deliver a blank or partial image on large or slow-rendering dashboards, while scheduled reports were already protected.

Root cause. AsyncExecuteReportScheduleCommand.run() built a ReportExecutionContext only when type == REPORT. Alerts ran with report_execution_context=None, and in superset/utils/screenshot_utils.py that None:

• selects the lenient readiness predicate (CHART_HOLDERS_READY_JS) instead of the fail-closed REPORT_CHART_HOLDERS_READY_JS, and
• sets allow_partial_fallback=True,

so partial/blank tiles were combined and delivered instead of failing.

Fix. Route alerts that deliver a rendered screenshot (PNG/PDF with ALERTS_ATTACH_REPORTS enabled) through the same execution context reports use, so a blank/incomplete capture raises ReportScheduleScreenshotFailedError and hands off to the existing retry/notification and error-handling machinery. The type == REPORT discriminator is replaced with an explicit "delivers a rendered artifact" check (_should_build_execution_context).

Deliberately left unchanged / lenient: CSV/text alerts, alerts without the attach flag, the non-delivered query-context capture (used to force a chart's saved query context), and UI thumbnails. Report behavior is unchanged (reports still always run under a context, regardless of format).

Secondary fix. ReportSuccessState (the Success/Grace path) logged ERROR on a delivery failure but did not notify the owner, unlike the first-run ReportNotTriggeredErrorState path which calls send_error(). A schedule whose previous run succeeded and then failed to deliver would fail silently — the common case once screenshots fail closed. The Success/Grace path now sends the owner error notification (respecting the error grace period), mirroring the first-run path.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Not applicable (no UI change).

TESTING INSTRUCTIONS

Automated (unit):

• _should_build_execution_context is True for all reports and for PNG/PDF alerts when ALERTS_ATTACH_REPORTS is enabled; False for CSV/text/xlsx alerts and for alerts with the flag off — see test_should_build_execution_context.
• The Success/Grace path notifies the owner on a delivery failure and respects the error grace period — see test_success_state_send_failure_notifies_owner and test_success_state_send_failure_skips_notification_in_error_grace.
• The delivered-screenshot fail-open vs fail-closed contract at the tile-combine layer is already covered in tests/unit_tests/utils/test_screenshot_utils.py.

Run:

pytest tests/unit_tests/commands/report/ \
       tests/unit_tests/utils/test_screenshot_utils.py \
       tests/unit_tests/utils/test_report_execution.py \
       tests/unit_tests/reports/

Manual: configure an alert with a PNG/PDF screenshot attachment (ALERTS_ATTACH_REPORTS on) against a large/slow dashboard. Instead of emailing a blank image, the execution now fails closed and follows the schedule's configured retry/error-notification behavior.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags: ALERTS_ATTACH_REPORTS (governs whether alerts attach a rendered screenshot; the fail-closed path applies only when it is enabled)
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

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[codecov]

Codecov Report

❌ Patch coverage is 31.81818% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.54%. Comparing base (bfa1e77) to head (4c5f317).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/commands/report/execute.py	31.81%	14 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #43031      +/-   ##
==========================================
- Coverage   66.59%   66.54%   -0.06%     
==========================================
  Files        2863     2864       +1     
  Lines      161734   161900     +166     
  Branches    37262    37301      +39     
==========================================
+ Hits       107712   107739      +27     
- Misses      51977    52116     +139     
  Partials     2045     2045              

Flag	Coverage Δ
hive	38.15% <4.54%> (-0.05%)	⬇️
mysql	57.67% <31.81%> (-0.09%)	⬇️
postgres	57.73% <31.81%> (-0.09%)	⬇️
presto	40.11% <4.54%> (-0.06%)	⬇️
python	59.11% <31.81%> (-0.10%)	⬇️
sqlite	57.34% <31.81%> (-0.09%)	⬇️
unit	100.00% <ø> (ø)

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