Checkpoint: production architecture

Checkpoint: production architecture

The last gate. Submit duplicates, exceed capacity, run everything: if all three counters come out exactly as the tests demand, you have implemented the core contracts of a production job platform — idempotency, backpressure, and exactly-once execution — in a form you can defend line by line.

Common failures: accepting duplicates (the seen-set came after the capacity check), counting rejections wrong (duplicates are rejected twice in the schedule: once per extra delivery), or double-executing because RunAll did not clear pending. Each maps to a real production bug with a real outage story.