Circuit Breaker. A boundary that stops calling, mutating, retrying, or enforcing through a failing dependency after declared failure conditions are met. A circuit breaker turns repeated failure into an explicit degraded state instead of letting the system keep applying pressure.
A circuit breaker is useful only when it is observable, recoverable, and tied to a governed path: what opens it, what work is refused or queued while it is open, who can reset it, and which source of record or health check proves the primary path is safe to resume. It should open within a named failure domain, not turn a local failure into a platform-wide outage. Its opening conditions belong in the retry policy, not in an unbounded loop.