fix(dashboard): batch virtualized chart force-render for large-dashboard export

[rusackas]

SUMMARY

Follow-up to #42561, stacked on top of it (base branch is upstream-fix-29719-force-render-export, not master, so this diff only shows what's new here).

#42561 fixes the client-side Download as Image/PDF path exporting virtualized dashboard rows as loading spinners, by forcing every row into view before capture. The fix is correct, but it forces every row into view in a single instant window event with no batching. On a dashboard with hundreds of charts, that reintroduces the exact thundering-herd load DASHBOARD_VIRTUALIZATION exists to prevent in the first place, just moved from page-load time to export time, with no concurrency limit and no signal to the user that anything expensive is about to happen.

This adds:

• Row-level batching. Rows now carry a data-row-id attribute; the export path force-renders them in groups of 5 rather than all at once, waiting (with a bounded 10s per-batch timeout) for each batch before moving to the next. The per-batch wait is scoped to just that batch's own row elements, not the whole container, so a chart stuck in one batch doesn't force every later batch to also burn its full timeout re-checking that same stale spinner (caught this via a failing test, not by inspection, see commit for details). Dashboards small enough to fit in one batch keep the original single-event behavior unchanged. The existing whole-container 60s check after all batches still runs as a final safety net.
• An upfront info toast ("Preparing N charts for export. This may take a moment.") when a multi-batch export starts, so the user gets a signal that a large export is underway rather than wondering if the click did nothing. A live per-batch progress bar felt like a bigger UI commitment than this follow-up warranted; forceLoadAllCharts now accepts an optional onProgress callback as an extensibility hook if that's wanted later.
• Test coverage for Row.tsx's event handling. fix(dashboard): force-render virtualized charts before client-side export #42561 added the force-in-view/restore-virtualization listeners to Row.tsx but never tested them directly, only the dispatching side in downloadUtils.test.ts. This adds coverage for the actual consumer: scoped batch targeting (responds only when its own row id is in the event, or when no rowIds filter is present at all) and observer re-attachment on restore.
• Test coverage for the batching logic: grouping into batches of 5, progress callback sequencing, per-batch timeout isolation (the bug mentioned above), and confirming the existing single-pass/flag-off paths from fix(dashboard): force-render virtualized charts before client-side export #42561 are unchanged.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A — this changes the pacing/signaling of an existing export flow, not its visual output.

TESTING INSTRUCTIONS

npx jest src/utils/downloadUtils.test.ts src/dashboard/components/gridComponents/Row/Row.test.tsx

Manually: with DASHBOARD_VIRTUALIZATION enabled, open a dashboard with more than 5 charts in one tab (enough to span multiple batches), and use Download → Export to Image/PDF. You should see a "Preparing N charts for export" toast, and the export should still contain every chart rendered (not loading spinners), same end result as #42561, just staggered.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• 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

🤖 Generated with Claude Code

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[bito-code-review]

The flagged issue is correct. The current implementation of forceLoadAllCharts in superset-frontend/src/utils/downloadUtils.ts already addresses this by introducing batching and a per-batch timeout (BATCH_LOAD_TIMEOUT_MS), followed by a final waitForChartsToLoad call that acts as the overall safety net. The implementation ensures that a slow chart in one batch does not block subsequent batches, and the final check ensures that any stragglers are accounted for before the export proceeds.

superset-frontend/src/utils/downloadUtils.ts

// eslint-disable-next-line no-await-in-loop -- see above
        await waitForRowsToLoad(batch, BATCH_LOAD_TIMEOUT_MS);
        onProgress?.({
          loadedBatches: index + 1,
          totalBatches: rowBatches.length,
        });
      }
    }
    const allLoaded = await waitForChartsToLoad(container);

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.28%. Comparing base (9b31f3b) to head (8569629).

Additional details and impacted files

@@                           Coverage Diff                           @@
##           upstream-fix-29719-force-render-export   #42786   +/-   ##
=======================================================================
  Coverage                                   65.27%   65.28%           
=======================================================================
  Files                                        2798     2798           
  Lines                                      158048   158088   +40     
  Branches                                    36114    36120    +6     
=======================================================================
+ Hits                                       103169   103205   +36     
- Misses                                      52884    52888    +4     
  Partials                                     1995     1995           

Flag	Coverage Δ
javascript	71.41% <100.00%> (+<0.01%)	⬆️

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