exemplar-harness-sdk 0.2.0

Exemplar harness eval SDK — ingest framework callbacks to the Exemplar platform API

exemplar-harness-sdk

Python SDK for ingesting framework-native agent telemetry into Exemplar harness eval.

Multiple framework integrations — LangChain, LangGraph, OpenAI, Anthropic, Google GenAI SDK, Google ADK, and more. See Framework integrations.

Install

pip install exemplar-harness-sdk

# One framework
pip install "exemplar-harness-sdk[langchain]"

# Everything
pip install "exemplar-harness-sdk[all]"

Licensed for non-commercial use only. Commercial use requires a separate license from Exemplar Dev LLC. See LICENSE.

---

Quick start

Follow these steps to send your first agent turn to Exemplar harness eval. The walkthrough uses LangChain; other frameworks follow the same pattern.

Step 1 — Install

pip install "exemplar-harness-sdk[langchain]"

Need a different framework? Install the matching extra instead (e.g. [anthropic], [openai], [google-adk]). See optional extras.

Step 2 — Configure credentials

Set your Exemplar org API key:

export EXEMPLAR_API_KEY="eis_your_org_api_key"

Variable	Purpose
EXEMPLAR_API_KEY	Org API key (required)

The SDK sends requests to https://production-api.exemplar.dev.

Step 3 — Create a Harness client

from exemplar_harness import Harness

harness = Harness.from_env()

Or pass the API key explicitly:

from exemplar_harness import Harness

harness = Harness(api_key="eis_...")

Pick one session_id per conversation — all turns with the same ID are grouped into a single eval session.

Step 4 — Wire the LangChain integration

Create a callback handler and pass it to your LLM or chain:

from exemplar_harness.integrations.langchain import make_langchain_callback_handler

SESSION_ID = "support-sess-001"  # reuse for every turn in this chat

handler = make_langchain_callback_handler(
    harness,
    session_id=SESSION_ID,
    chain_name="support-bot",
    source_app="my-app",
)

Each completed LLM call invokes Harness.ingest() automatically — you do not call ingest() yourself for callback-based integrations.

Step 5 — Run your agent

from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI  # or ChatGoogleGenerativeAI, etc.

llm = ChatOpenAI(model="gpt-4o", callbacks=[handler])
chain = ChatPromptTemplate.from_messages([("human", "{question}")]) | llm

chain.invoke({"question": "Summarize our refund policy."})
chain.invoke({"question": "What is the return window?"})  # same SESSION_ID → same eval session

Step 6 — (Optional) Trigger eval on ingest

Pass auto_run=True when you call harness.ingest() directly, or bind it on a session helper:

session = harness.session(
    SESSION_ID,
    agent_name="support-bot",
    source_app="my-app",
    auto_run=True,  # run eval after each ingest through this session
)

Callback-based integrations (LangChain, LangGraph, Agno, etc.) call harness.ingest() internally with platform defaults.

What happens under the hood

flowchart LR
  Agent[Your agent] --> Integration[SDK integration]
  Integration --> Harness[Harness.ingest]
  Harness --> API[Exemplar platform API]
  API --> Eval[Harness eval]

Each ingest POSTs an envelope v1 payload (sourceType + framework-native data). The Exemplar platform API maps it to eval session turns.

A successful ingest returns metadata such as sessionId, turnCount, and evalStatus.

Complete example (steps 3–5)

from exemplar_harness import Harness
from exemplar_harness.integrations.langchain import make_langchain_callback_handler
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI

harness = Harness.from_env()
session_id = "support-sess-001"

handler = make_langchain_callback_handler(
    harness,
    session_id=session_id,
    chain_name="support-bot",
    source_app="my-app",
)

llm = ChatOpenAI(model="gpt-4o", callbacks=[handler])
chain = ChatPromptTemplate.from_messages([("human", "{question}")]) | llm

for question in (
    "Summarize our refund policy.",
    "What is the return window?",
):
    chain.invoke({"question": question})

No framework? Ingest turns directly

For fixtures, batch replay, or custom pipelines:

harness.ingest(
    "generic",
    session_id="sess-abc",
    event="turns",
    data={
        "turns": [
            {
                "input": "What is harness eval?",
                "output": "Automated judge over agent sessions.",
                "model": "gpt-4o",
            }
        ]
    },
    agent_name="my-agent",
    source_app="my-app",
)

Choose a different framework

Framework	Extra	Wire this
LangChain	langchain	make_langchain_callback_handler → callbacks=[handler]
LangGraph	langgraph	HarnessLangGraphHandler.make_graph_callback_handler() → invoke(..., config={"callbacks": [...]})
LiteLLM	litellm	register_litellm_handler + metadata={"session_id": ...}
OpenAI SDK	openai	HarnessOpenAICallback.on_completion after chat.completions.create
Anthropic SDK	anthropic	make_anthropic_middleware → Anthropic(middleware=[...])
Claude Agent SDK	claude-agent	run_query() or record_agent_result after query()
Portkey	portkey	HarnessPortkeyCallback.on_completion after chat.completions.create
Agno	agno	harness_agno_post_hook → Agent.post_hooks
Haystack	haystack	HarnessHaystackHandler.run_and_record or record_generator_run
LlamaIndex	llamaindex	register_llamaindex_handler (auto) or record_llm_chat_end
AutoGen	autogen	HarnessAutoGenHandler.on_agent_run_complete after agent.run
CrewAI	crewai	make_crewai_listener (auto) or on_task_complete
Google GenAI SDK	google-genai	instrument_google_genai_client or sdk_generate_content
Google ADK	google-adk	ingest_adk_session after session.model_dump()
Pydantic AI	pydantic-ai	instrument_pydantic_ai_agent or record_run after agent.run
Semantic Kernel	semantic-kernel	register_semantic_kernel_filter on Kernel
smolagents	smolagents	harness_smolagents_step_callback → step_callbacks

Copy-paste snippets for each framework are in Framework integrations below.

Ingest parameters

Parameter	Purpose
session_id	Groups turns into one eval session
agent_name	Agent identifier on the ingest body
source_app	Your application name (defaults to source_type)
auto_run	Run eval immediately after ingest (True / False / omit)
harness	Optional eval metadata (scenario tags, categories, etc.)

---

Harness memory (long-term recall)

The SDK can add and search long-term memories via the integration-service memory API (/api/harness-memory). Eval ingest (Harness.ingest()) is unchanged.

Configure

export EXEMPLAR_API_KEY="eis_your_org_api_key"
# optional for JWT auth or explicit org override:
# export EXEMPLAR_ORGANIZATION_ID="your_org_id"
# optional for local dev:
export EXEMPLAR_BASE_URL="http://localhost:8000"

Variable	Purpose
EXEMPLAR_API_KEY	Org API key (required)
EXEMPLAR_ORGANIZATION_ID	Optional org override (JWT auth); omitted when using org API keys
EXEMPLAR_BASE_URL	Override API host (default: production)

Add, search, recall

from exemplar_harness import Harness

harness = Harness.from_env()  # org API key is enough; organization_id optional
memory = harness.memory(user_id="user-123", session_id="chat-abc", app_id="my-app")

memory.add("User prefers bullet-point answers.", memory_type="preference")
results = memory.search("formatting preferences", top_k=5)
context = memory.recall("how should I format answers?")  # for system prompts

Generic hook (any agent loop)

from exemplar_harness.integrations.memory import MemoryHook

hook = MemoryHook(memory, recall_top_k=5, auto_add=False)
recall = hook.before_turn(user_input)          # inject into system prompt
# ... run LLM ...
hook.after_turn(user_input, assistant_output)  # no-op unless auto_add=True

LangChain

from exemplar_harness.integrations.memory.langchain import make_langchain_memory_handler

handler = make_langchain_memory_handler(harness, user_id="user-123", session_id="chat-abc")
recall = handler.recall_for("What do you know about me?")
# pass handler in callbacks=[handler]; prepend handler.system_prompt_prefix() to system message

LiteLLM

from exemplar_harness.integrations.memory.litellm import make_litellm_memory_logger

mem_logger = make_litellm_memory_logger(harness, user_id="user-123")
messages = mem_logger.prepare_messages([{"role": "user", "content": "Hello"}])
# register_litellm_memory_logger(harness, user_id="user-123") for global callbacks

Framework memory helpers

Each eval integration has a matching memory helper under exemplar_harness.integrations.memory.*:

Framework	Import	Wire this
Generic	MemoryHook	before_turn / after_turn on any loop
LangChain	make_langchain_memory_handler	callbacks=[handler] + recall_for()
LangGraph	make_langgraph_memory_handler	same as LangChain in graph config
LiteLLM	make_litellm_memory_logger	prepare_messages() or register_litellm_memory_logger
OpenAI SDK	make_openai_memory_helper	sdk_chat_completion_with_memory(helper, client, ...)
Anthropic SDK	make_anthropic_memory_helper	make_anthropic_memory_middleware(helper)
Portkey	make_portkey_memory_helper	same pattern as OpenAI
Google GenAI	make_google_genai_memory_helper	prepare_contents() / sdk_generate_content_with_memory
Agno	make_agno_memory_helper	harness_agno_memory_hooks(helper) pre/post hooks
Pydantic AI	make_pydantic_ai_memory_helper	prepare_prompt() before agent.run()
Haystack	make_haystack_memory_helper	prepare_generator_messages() before generator run
LlamaIndex	make_llamaindex_memory_helper	prepare_chat_messages() before chat
AutoGen	make_autogen_memory_helper	prepare_task() before agent run
CrewAI	make_crewai_memory_helper	prepare_task_context() before task
smolagents	make_smolagents_memory_helper	harness_smolagents_memory_step_callback(helper)
Semantic Kernel	make_semantic_kernel_memory_helper	prepare_arguments() before invoke
Claude Agent SDK	make_claude_agent_memory_helper	prepare_prompt() before query()
Google ADK	make_google_adk_memory_helper	prepare_user_message() before turn

Live examples: examples/live/memory_demo.py, examples/live/langchain_memory_demo.py, and:

python -m examples.live.run_memory_demos --list
HARNESS_EXAMPLES_SIMULATED=1 python -m examples.live.run_memory_demos
EXEMPLAR_API_KEY=... GOOGLE_API_KEY=... python -m examples.live.run_memory_demos --only memory_google_genai

---

Framework integrations

Step-by-step quick start above uses LangChain. Below are equivalent snippets for each supported framework.

LangChain

Already covered in Quick start. Minimal reference:

from exemplar_harness.integrations.langchain import make_langchain_callback_handler
from langchain_openai import ChatOpenAI

handler = make_langchain_callback_handler(harness, session_id="sess-abc", chain_name="support-bot")
llm = ChatOpenAI(model="gpt-4o", callbacks=[handler])

LangGraph

pip install "exemplar-harness-sdk[langgraph]"

Pass make_graph_callback_handler() in your graph invoke config:

from typing import Annotated, TypedDict

from exemplar_harness import Harness
from exemplar_harness.integrations.langgraph import HarnessLangGraphHandler
from langchain_core.messages import HumanMessage
from langchain_openai import ChatOpenAI
from langgraph.graph import END, START, StateGraph
from langgraph.graph.message import add_messages

harness = Harness(api_key="eis_...")
session = HarnessLangGraphHandler(harness, session_id="sess-abc", graph_name="support-bot")
handler = session.make_graph_callback_handler()
config = {"callbacks": [handler], "configurable": {"thread_id": "sess-abc"}}

llm = ChatOpenAI(model="gpt-4o")


class State(TypedDict):
    messages: Annotated[list, add_messages]


def agent(state: State, run_config):
    return {"messages": [llm.invoke(state["messages"], config=run_config)]}


graph = StateGraph(State)
graph.add_node("agent", agent)
graph.add_edge(START, "agent")
graph.add_edge("agent", END)
app = graph.compile()

app.invoke(
    {"messages": [HumanMessage(content="Summarize our refund policy.")]},
    config=config,
)

LiteLLM

pip install "exemplar-harness-sdk[litellm]"

Register a custom logger once; pass session_id in completion metadata:

import litellm
from exemplar_harness import Harness
from exemplar_harness.integrations.litellm import register_litellm_handler

harness = Harness(api_key="eis_...")
register_litellm_handler(harness, source_app="my-app", agent_name="support-bot")

litellm.completion(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Summarize our refund policy."}],
    metadata={"session_id": "sess-abc"},
)

Anthropic SDK

pip install "exemplar-harness-sdk[anthropic]"

One HarnessAnthropicCallback per session. Prefer client middleware for automatic ingest:

import anthropic
from exemplar_harness import Harness
from exemplar_harness.integrations.anthropic import (
    HarnessAnthropicCallback,
    make_anthropic_middleware,
)

harness = Harness(api_key="eis_...")
callback = HarnessAnthropicCallback(harness, session_id="sess-abc", agent_name="support-bot")

client = anthropic.Anthropic(middleware=[make_anthropic_middleware(callback)])
response = client.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Summarize our refund policy."}],
)

Or call on_completion manually after each messages.create if you cannot use middleware.

Claude Agent SDK

pip install "exemplar-harness-sdk[claude-agent]"

Use run_query to run the agent and ingest automatically:

import asyncio

from exemplar_harness import Harness
from exemplar_harness.integrations.claude_agent import HarnessClaudeAgentHandler

harness = Harness(api_key="eis_...")
handler = HarnessClaudeAgentHandler(harness, session_id="sess-abc", agent_name="research-agent")

asyncio.run(handler.run_query("Summarize harness eval in one sentence."))

Or call record_agent_result manually after query() returns a ResultMessage:

import asyncio

from claude_agent_sdk import ResultMessage, query
from exemplar_harness import Harness
from exemplar_harness.integrations.claude_agent import HarnessClaudeAgentHandler

harness = Harness(api_key="eis_...")
handler = HarnessClaudeAgentHandler(harness, session_id="sess-abc", agent_name="research-agent")


async def main() -> None:
    prompt = "Summarize harness eval in one sentence."
    result = None
    async for message in query(prompt=prompt):
        if isinstance(message, ResultMessage):
            result = message
    handler.record_agent_result(prompt=prompt, result=result)


asyncio.run(main())

OpenAI SDK

pip install "exemplar-harness-sdk[openai]"

Call on_completion after each chat.completions.create:

from openai import OpenAI
from exemplar_harness import Harness
from exemplar_harness.integrations.openai import HarnessOpenAICallback

harness = Harness(api_key="eis_...")
callback = HarnessOpenAICallback(harness, session_id="sess-abc", agent_name="support-bot")

client = OpenAI()
messages = [{"role": "user", "content": "Summarize our refund policy."}]
response = client.chat.completions.create(model="gpt-4o", messages=messages)

callback.on_completion(messages=messages, response=response, model="gpt-4o")

Portkey

pip install "exemplar-harness-sdk[portkey]"

Call on_completion after each chat.completions.create:

import os

from portkey_ai import Portkey
from exemplar_harness import Harness
from exemplar_harness.integrations.portkey import HarnessPortkeyCallback

harness = Harness(api_key="eis_...")
callback = HarnessPortkeyCallback(harness, session_id="sess-abc", agent_name="support-bot")

client = Portkey(api_key=os.environ["PORTKEY_API_KEY"])
messages = [{"role": "user", "content": "Summarize our refund policy."}]
response = client.chat.completions.create(model="@openai/gpt-4o", messages=messages)

callback.on_completion(messages=messages, response=response, model="@openai/gpt-4o")

Agno

pip install "exemplar-harness-sdk[agno]"

Pass harness_agno_post_hook to Agent.post_hooks — each agent.run ingests automatically:

from agno.agent import Agent
from agno.models.openai import OpenAIChat
from exemplar_harness import Harness
from exemplar_harness.integrations.agno import harness_agno_post_hook

harness = Harness(api_key="eis_...")
agent = Agent(
    name="support-bot",
    model=OpenAIChat(id="gpt-4o"),
    post_hooks=[
        harness_agno_post_hook(harness, session_id="sess-abc", agent_name="support-bot")
    ],
)

agent.run("Summarize our refund policy.")

Haystack

pip install "exemplar-harness-sdk[haystack]"

Use run_and_record to run the pipeline and ingest in one call:

from haystack import Pipeline
from haystack.components.builders import ChatPromptBuilder
from haystack.components.generators.chat import OpenAIChatGenerator
from haystack.dataclasses import ChatMessage
from exemplar_harness import Harness
from exemplar_harness.integrations.haystack import HarnessHaystackHandler

harness = Harness(api_key="eis_...")
handler = HarnessHaystackHandler(harness, session_id="sess-abc", pipeline_name="support-bot")

prompt_builder = ChatPromptBuilder(
    template=[ChatMessage.from_user("{{ question }}")],
    required_variables=["question"],
)
llm = OpenAIChatGenerator(model="gpt-4o")
pipe = Pipeline()
pipe.add_component("prompt_builder", prompt_builder)
pipe.add_component("llm", llm)
pipe.connect("prompt_builder.prompt", "llm.messages")

question = "Summarize our refund policy."
handler.run_and_record(pipe, {"prompt_builder": {"question": question}}, question=question)

You can also call record_generator_run manually after pipe.run, or pass handler.make_snapshot_callback(question=...) to pipe.run(..., snapshot_callback=...).

LlamaIndex

pip install "exemplar-harness-sdk[llamaindex]"

Register instrumentation once; LlamaIndex LLM calls ingest automatically:

from exemplar_harness import Harness
from exemplar_harness.integrations.llamaindex import register_llamaindex_handler
from llama_index.core.llms import ChatMessage
from llama_index.llms.openai import OpenAI

harness = Harness(api_key="eis_...")
register_llamaindex_handler(harness, session_id="sess-abc", workflow_name="support-workflow")

llm = OpenAI(model="gpt-4o")
messages = [ChatMessage(role="user", content="Summarize our refund policy.")]
llm.chat(messages)

Or call record_llm_chat_end manually after each llm.chat if you prefer explicit control.

AutoGen

pip install "exemplar-harness-sdk[autogen]"

Call on_agent_run_complete after each agent.run:

import asyncio

from autogen_agentchat.agents import AssistantAgent
from autogen_ext.models.openai import OpenAIChatCompletionClient
from exemplar_harness import Harness
from exemplar_harness.integrations.autogen import HarnessAutoGenHandler

harness = Harness(api_key="eis_...")
handler = HarnessAutoGenHandler(
    harness, session_id="sess-abc", agent_name="assistant", team_name="support-team"
)


async def run() -> None:
    client = OpenAIChatCompletionClient(model="gpt-4o")
    agent = AssistantAgent(name="assistant", model_client=client)
    try:
        task = "Summarize our refund policy."
        result = await agent.run(task=task)
        handler.on_agent_run_complete(task=task, result=result, model="gpt-4o")
    finally:
        await client.close()


asyncio.run(run())

CrewAI

pip install "exemplar-harness-sdk[crewai]"

Register a CrewAI event listener for automatic ingest on TaskCompletedEvent:

from exemplar_harness import Harness
from exemplar_harness.integrations.crewai import make_crewai_listener

harness = Harness(api_key="eis_...")
monitor = make_crewai_listener(
    harness, session_id="sess-abc", crew_name="research-crew", model="gpt-4o"
)

# Run your crew — task completions ingest automatically via the listener.

Or call on_task_complete manually when each task finishes:

from exemplar_harness.integrations.crewai import HarnessCrewAIMonitor

monitor = HarnessCrewAIMonitor(
    harness, session_id="sess-abc", crew_name="research-crew", model="gpt-4o"
)
monitor.on_task_complete(
    agent_role="Researcher",
    task_description="Summarize our refund policy.",
    output="Our policy allows returns within 30 days.",
    prompt_tokens=120,
    completion_tokens=45,
)

Google GenAI SDK

pip install "exemplar-harness-sdk[google-genai]"

Use instrument_google_genai_client so each generate_content call ingests automatically:

from google import genai
from exemplar_harness import Harness
from exemplar_harness.integrations.google_genai import (
    HarnessGoogleGenAICallback,
    instrument_google_genai_client,
)

harness = Harness(api_key="eis_...")
callback = HarnessGoogleGenAICallback(harness, session_id="sess-abc", agent_name="support-bot")

client = genai.Client(api_key="your-google-api-key")
instrument_google_genai_client(callback, client)

response = client.models.generate_content(
    model="gemini-2.5-flash",
    contents="Summarize our refund policy.",
)
print(response.text)

Or wrap a single call with sdk_generate_content if you prefer not to patch the client.

Google ADK

pip install "exemplar-harness-sdk[google-adk]"

Run your ADK agent, then export and ingest the session:

import asyncio

from exemplar_harness import Harness
from exemplar_harness.integrations.google_adk import ingest_adk_session
from google.adk.agents import LlmAgent
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
from google.genai import types

harness = Harness(api_key="eis_...")
session_id, app_name, user_id = "sess-abc", "my_app", "user-1"

agent = LlmAgent(
    model="gemini-2.5-flash",
    name="my_agent",  # must be a valid Python identifier
    instruction="Answer concisely.",
)
sessions = InMemorySessionService()


async def run_and_ingest() -> None:
    await sessions.create_session(app_name=app_name, user_id=user_id, session_id=session_id)
    runner = Runner(agent=agent, app_name=app_name, session_service=sessions)

    message = types.Content(role="user", parts=[types.Part(text="Hello")])
    async for _ in runner.run_async(user_id=user_id, session_id=session_id, new_message=message):
        pass

    session = await sessions.get_session(app_name=app_name, user_id=user_id, session_id=session_id)
    ingest_adk_session(
        harness,
        session.model_dump(mode="json", exclude_none=True),
        session_id=session_id,
        agent_name="my-agent",
    )


asyncio.run(run_and_ingest())

If you already have a session export dict:

ingest_adk_session(harness, adk_session, session_id="sess-abc", agent_name="my-agent")

Pydantic AI

pip install "exemplar-harness-sdk[pydantic-ai]"

Instrument the agent so each run / run_sync ingests automatically:

from pydantic_ai import Agent
from exemplar_harness import Harness
from exemplar_harness.integrations.pydantic_ai import (
    HarnessPydanticAIHandler,
    instrument_pydantic_ai_agent,
)

harness = Harness(api_key="eis_...")
handler = HarnessPydanticAIHandler(harness, session_id="sess-abc", agent_name="support-bot")
agent = Agent("google:gemini-2.5-flash")
instrument_pydantic_ai_agent(handler, agent)

agent.run_sync("Summarize our refund policy.")

Semantic Kernel

pip install "exemplar-harness-sdk[semantic-kernel]"

Register a function-invocation filter on your kernel:

from semantic_kernel import Kernel
from exemplar_harness import Harness
from exemplar_harness.integrations.semantic_kernel import register_semantic_kernel_filter

harness = Harness(api_key="eis_...")
kernel = Kernel()
register_semantic_kernel_filter(kernel, harness, session_id="sess-abc", plugin_name="my-plugin")

# Each kernel.invoke(...) ingests automatically after the function runs.

smolagents

pip install "exemplar-harness-sdk[smolagents]"

Pass a step callback when creating your agent:

from smolagents import CodeAgent
from exemplar_harness import Harness
from exemplar_harness.integrations.smolagents import harness_smolagents_step_callback

harness = Harness(api_key="eis_...")
agent = CodeAgent(
    tools=[],
    model=model,
    step_callbacks=[
        harness_smolagents_step_callback(harness, session_id="sess-abc", agent_name="support-bot")
    ],
)
agent.run("Summarize our refund policy.")

---

Reference

Optional extras

Extra	Module
langchain	exemplar_harness.integrations.langchain
langgraph	exemplar_harness.integrations.langgraph
litellm	exemplar_harness.integrations.litellm
openai	exemplar_harness.integrations.openai
anthropic	exemplar_harness.integrations.anthropic
claude-agent	exemplar_harness.integrations.claude_agent
portkey	exemplar_harness.integrations.portkey
agno	exemplar_harness.integrations.agno
haystack	exemplar_harness.integrations.haystack
llamaindex	exemplar_harness.integrations.llamaindex
autogen	exemplar_harness.integrations.autogen
crewai	exemplar_harness.integrations.crewai
google-adk	exemplar_harness.integrations.google_adk
google-genai	exemplar_harness.integrations.google_genai
pydantic-ai	exemplar_harness.integrations.pydantic_ai
semantic-kernel	exemplar_harness.integrations.semantic_kernel
smolagents	exemplar_harness.integrations.smolagents

Vercel AI SDK is not included in the Python package (TypeScript SDK path).

Envelope v1

Each ingest POSTs schemaVersion: 1 to POST /api/harness-eval/v1/sessions with a sourceType and framework-native data payload. The Exemplar platform API maps envelopes to EvalSession turns.