Framework vs. runtime vs. harness

A clarifying conceptual hierarchy, taught through the canonical open-source example.
A framework provides abstractions for building agents; a runtime provides
production infrastructure such as durable execution, streaming, and
human-in-the-loop; a harness is an opinionated, batteries-included agent that
runs out of the box. The LangChain stack maps onto these three layers exactly —
LangChain (framework), LangGraph (runtime), and DeepAgents (harness) — which makes
the otherwise-abstract word "harness" concrete.