Implements LangGraph cast components following systematic workflow (state, deps, nodes, conditions, graph). Use when implementing cast, building nodes/agents/tools, need LangGraph patterns (memory, retry, guardrails, vector stores), or ask "implement cast", "build graph", "add node".

Implements DeepAgent components using LangChain's deepagents SDK. Use when building deep agents with create_deep_agent, configuring backends/subagents/skills/memory, need DeepAgent patterns (sandbox, HITL interrupts, long-term memory, subagent spawning), or ask "implement deep agent", "add subagent", "configure backend".

Implements LangGraph v2 streaming for graphs with subgraphs and agents. Use when adding streaming to runtime/API endpoint, need token streaming, custom stream events, namespace parsing, or ask "add streaming", "stream tokens", "stream graph".

Guides pytest test writing for LangGraph casts with mocking patterns for LLM/API/Store calls. Use when writing tests, need mock strategies, setting up fixtures, testing nodes/graphs, or ask "write tests", "mock LLM", "test coverage".