Module reliability 

Reliability tier: retry with backoff + jitter, circuit breaker. Reliability tier: backpressure (bounded backend concurrency), retry with exponential backoff + jitter, and a closed/open/half-open circuit breaker around backend operations.

All three are composed by a private ReliableBackend decorator around any crate::backend::Backend, applied by the builder when a ReliabilityConfig is set (see crate::CacheKitBuilder::reliability). The intent presets production, encrypted, and io enable it by default; minimal does not — mirroring the TypeScript SDK’s preset posture.

Composition order is backpressure(breaker(retry(op))):

• The retry loop is inside the breaker (matching the TypeScript SDK’s ReliabilityExecutor), so one exhausted retry sequence counts as a single breaker failure, and a fast-failing open breaker never spends time retrying.
• The concurrency limiter is outermost: one permit per logical cache operation, held across the entire breaker/retry sequence. That bounds in-flight work including retry amplification (K callers mid-backoff are still K permits — new work queues behind them instead of piling onto a struggling backend), and a shed call never touches breaker counters or half-open probe slots, so the breaker keeps measuring backend health, not caller-side overload. A permit holder never re-enters the limiter (backend ops don’t nest), so holding permits across retry backoff cannot deadlock.

Unlike the TypeScript breaker (which counts every error), only errors classified retryable by crate::error::BackendErrorKind::is_retryable (Transient, Timeout) count toward opening the circuit: they are the backend-health signals. Permanent / Authentication errors are request-specific — five malformed requests must not cut off healthy traffic.

Requires a tokio runtime for backoff timers (redis and cachekitio backends already do). Not available on wasm32 targets.

Structs

BackpressureConfig

Backpressure configuration: bound how many backend data operations may be in flight at once, so a slow or failing backend cannot exhaust the caller’s connection pool or memory.

CircuitBreakerConfig

Circuit breaker configuration.

ReliabilityConfig

Reliability stack configuration: which layers to apply around backend ops.

RetryConfig

Retry policy configuration (truncated exponential backoff with jitter).