Chunked Promise.allSettled with a UI yield between batches. ops/s is computed over pure write time (yields excluded), failures are counted separately.
While two peers are online together, changes travel live as upsert op
batches — delta/full-state are catch-up messages for missed history. To see them: connect a second
browser, close it, insert items here, then reopen it — bulks within
oplogSize arrive as deltaSync; larger ones force a fullStateSync.
Verifies structuredClone deep copy and MessagePack persistence for Date and nested structures.
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