Implements a BaseContext class that manages per-subclass ContextVar instances, supporting nesting, async context switching, and cleanup. This is a reusable pattern for any Python application needing isolated context per class hierarchy (e.g., request-scoped state, transaction contexts). It demonstrates non-obvious skill in leveraging ContextVar with metaclass-like per-class storage.

Defines a Transport protocol (Request/Response dataclasses, TransportError hierarchy) with both async and sync implementations (aiohttp, httpx, httpx2). The abstraction is clean, minimal, and easily extensible to new HTTP backends. Reusable for any API client that needs to support multiple HTTP libraries without coupling to a specific one.

Implements a Postgres LISTEN/NOTIFY listener with exponential backoff, connection pool awareness, and graceful shutdown. This is a reusable component for any application needing inter-process notifications via Postgres, demonstrating careful handling of connection lifecycle and backoff strategies.

Provides an A/B benchmark runner that interleaves execution of two test subjects to mitigate machine drift and produce statistically sound comparisons. It includes warmup, measurement phases, and result aggregation. This is a reusable pattern for any performance testing framework that needs to compare two versions of code under noisy environments.

A vendored lazy module loader (from Scientific Python) that defers module imports until attribute access, supporting PEP 810 compatibility. It provides a clean API (attach, LazyModule) and handles edge cases like submodule imports and error propagation. Reusable for any Python project that wants to reduce startup time by lazily importing heavy modules.