Defines the core interceptor interface and a chain builder for composing middleware. Includes conditional combinators (If, And, Or, Not, IsMethod) that allow fine-grained control over interceptor application. This pattern is self-contained (only depends on standard library and a simple Method type) and can be extracted for use in any Go server or RPC framework requiring a flexible middleware pipeline.

Provides a generic, thread-safe singleton factory using sync.Mutex and lazy initialization. The implementation is minimal and correct, handling double-checked locking and reset functionality. It can be extracted and reused anywhere a single instance of a type needs to be managed across goroutines.

Implements a sliding window data structure for counting events over time, using a ring buffer of buckets. Supports time-based and point-based window policies. This is a foundational component for rate limiting and metrics aggregation, and can be extracted for other projects needing rolling window calculations.

A state-machine implementation of the circuit breaker pattern with Closed/Open/HalfOpen states, failure counting, and automatic recovery. Uses a rolling window to track recent failures. The logic is self-contained (depends only on the rolling package) and can be extracted for resilience in any Go service.