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Tutorial: Sync Harness LangGraph Agent

This tutorial demonstrates how to build a synchronous LangGraph agent on AgentEx using the unified harness surface:

turn = LangGraphTurn(stream, model=None)
emitter = UnifiedEmitter(task_id=task_id, trace_id=task_id, ...)
async for event in emitter.yield_turn(turn):
    yield event

Compare with 030_langgraph, which uses the bespoke convert_langgraph_to_agentex_events helper directly.

Key Concepts

Unified Harness

LangGraphTurn implements the HarnessTurn protocol: it wraps the raw LangGraph astream() generator and exposes events (an async generator of TaskMessageUpdate) and usage() (token counts captured from the final AIMessage).

UnifiedEmitter.yield_turn(turn) iterates the turn's events and yields them to the sync ACP handler unchanged. The same LangGraphTurn object can also be passed to UnifiedEmitter.auto_send_turn in the async/temporal channels.

AGX1-377 Note

LangGraph emits tool requests as StreamTaskMessageFull events (from "updates" node outputs). The SpanDeriver does not open tool spans from Full events today; that gap is tracked in AGX1-373.

Files

File Description
project/acp.py ACP server using unified harness (LangGraphTurn + yield_turn)
project/graph.py LangGraph state graph (identical to 030_langgraph)
project/tools.py Tool definitions (weather example)
tests/test_agent.py Integration tests
manifest.yaml Agent configuration (name: s-harness-langgraph)

Running Locally

agentex agents run

Running Tests

pytest tests/test_agent.py -v