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The Wikimedia feed's thumbnail is 330px, which upscales blurry in our hero. Use originalimage.source instead — it's reliably sharp. (Can't just request a bigger thumbnail width: for very large source images Wikimedia only serves pre-generated bucket sizes and 400s on arbitrary widths — e.g. 500px ok, 800/1024px fail.) - onthisday._best_image() prefers originalimage, falls back to the thumbnail. - scripts/otd_image_upsize_backfill.py re-fetches each stored MM-DD and upgrades image_url in onthisday_pool + daily_onthisday in place (ran on host: pool + 6 daily rows now sharp; today's hero verified 200). Only the /onthisday hero loads this image (home card is text-only), so larger files are a single-page, one-time load. - test_best_image locks the prefer-original/fallback behavior. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>