Topic
Lost-update races where concurrent read-modify-write sequences each succeed but overwrite one another's results.
Duplicate side effects all return 200, so nothing alerts on them. The write side of a file-based guard is a single O_EXCL create and it holds under forty processes; every defect four review rounds found afterwards sat in reclaim and in reads.
Reality
Umair Rafi's Python walkthrough gets the contract right, and the interesting failure is what a duplicate sees while the charge is still in flight, when the replay branch fires before there is anything stored to replay.
Reality
Vestibule's suite was green while pip install was broken. An AI reviewer caught a 390-second race in a design document, because someone had written the document.
Reality
A shared circuit breaker looks like a three-state machine until a stale decision lands on a fresh half-open period and kills a recovery it never observed.
Reality
A hackathon Electron app wrote every file successfully and still lost workspaces. The defect lived in the gap between an operation finishing and its result surviving.
Reality