LangChain 1.4.0 adds a first-party MCP namespace

LangChain 1.4.0 introduced the langchain.mcp namespace and MCPAdapter, added runnable examples, changed middleware tracing to omit inputs, and included the model destination in tool routing.

Why it matters: first-party Model Context Protocol support reduces glue code, while tracing and routing changes can alter observability and policy enforcement.

Impact: run integration regression tests and confirm trace redaction before upgrading. Official GitHub releases