---
status: accepted
supersedes: ADR-0001
---

# LangGraph holds Execution state; ADK agents reason and act

An Execution is a hierarchy of ReAct agents shaped by the dependencies between Deliverables ([ADR-0002](0002-skills-are-the-portable-unit-of-behaviour.md)).

- **LangGraph holds the Execution.** A LangGraph `StateGraph` holds the dependency graph and each Deliverable's state. It checkpoints after every step and pauses with `interrupt()` whenever the user must answer or approve. This follows the KAB workflow standard and the platform's `langgraph-workflow-agent`.
- **ADK agents reason and act.** The Orchestrator and every Specialist is an ADK `LlmAgent`, each running its own ReAct loop, with a `SkillToolset` for progressive Skill loading. This follows the platform's `google-adk-base-agent/app/skills_integration.py`.
- **Agents sit behind one interface.** Each agent runs behind a single agent-runtime interface, so LangChain Deep Agents can be added as a second implementation without touching the graph.

The dependency graph is declared as data in code. The Orchestrator picks what to do next through tools that refuse work whose dependencies aren't met. Dependencies are guaranteed by code, while ordering and parallelism are the model's choice.

## Considered Options

- **ADK end to end** (root `LlmAgent` with `sub_agents`/`AgentTool`, and ADK sessions for pauses): rejected. It departs from the KAB workflow standard, and LangGraph's checkpointed `interrupt()` is the proven platform path for resumable user Approvals.
- **Deep Agents end to end** (`create_deep_agent(skills=, subagents=)`): viable, and it compiles to LangGraph. It was deferred rather than rejected: ADK `SkillToolset` already has working prior art on this platform, and Deep Agents stays reachable as the second implementation of the agent-runtime interface.
- **Code runs the dependency graph with no Orchestrator model**: rejected. The top level wouldn't be ReAct, and the Skill's conversational flexibility (such as skipping work the user says is already approved) would need hand-coding.

## Consequences

- There are two frameworks in one process. Framework types stay inside the agent-runtime implementation and never appear in graph state.
- ADK Skills are *Experimental* (Python ≥ 1.25.0), so pin the version.