LangGraph runtime does not enforce EndNode output schema constraints #233

The LangGraph Agent Spec runtime does not enforce the schema declared on an EndNode when returning the final flow output.

A minimal flow was created with:

• A permissive StartNode schema, allowing the test payload to enter the flow.
• A strict EndNode schema requiring:
  • name
  • profile
  • profile.score
  • profile.active
  • profile.tags
• A direct DataFlowEdge from the StartNode payload to the EndNode.

The serialized Agent Spec correctly contains the strict schema on the EndNode, including:

{
  "required": ["name", "profile"],
  "properties": {
    "profile": {
      "required": ["score", "active", "tags"]
    }
  }
}

Valid case

The following payload conforms to the EndNode schema:

{
  "name": "Ada",
  "profile": {
    "score": 0.98,
    "active": true,
    "tags": ["verified", "structured"]
  }
}

Both LangGraph and Wayflow successfully return this payload.

Invalid case

The following payload is intentionally missing the required nested field profile.active:

{
  "name": "Ada",
  "profile": {
    "score": 0.98,
    "tags": ["verified", "structured"]
  }
}

The permissive StartNode allows this value to enter the flow. The value then reaches an EndNode whose declared schema requires profile.active.

Expected Behavior

The runtime should reject the value at the EndNode boundary because it does not conform to the EndNode's declared output schema.

The invalid value should not be returned as a successful flow output.

Actual Behavior

LangGraph

LangGraph accepts the invalid value and successfully completes the flow:

AgentSpecFinishedExecutionStatus(
    outputs={
        "payload": {
            "name": "Ada",
            "profile": {
                "score": 0.98,
                "tags": ["verified", "structured"]
            }
        }
    },
    agent_messages=[]
)

No validation error is raised even though the returned value violates the EndNode schema.

Wayflow

Wayflow rejects the same value with a TypeError because it does not satisfy the expected ObjectProperty.

This is the expected behavior.

Runtime Comparison

Impact

An Agent Spec flow executed by the LangGraph runtime can successfully return values that violate the schema explicitly declared by its EndNode.

This makes the EndNode output contract unenforced and produces different behavior for the same Agent Spec across runtimes.