Prompt for human feedback in LangGraph Functional API HITL sample (#368)

* Prompt for human feedback in LangGraph Functional API HITL sample

* Make LangGraph HITL samples model-free

Rewrite both graph_api and functional_api human-in-the-loop samples to be deliberately model-free without requiring an Anthropic API key. Draft generation and revision use deterministic templates while preserving the interactive terminal review workflow. Update unit tests and documentation accordingly.

* Fix mypy attribute error in functional HITL test fixture

Author: musi22

langgraph_plugin/functional_api/human_in_the_loop/README.md

@@ -22,17 +22,19 @@ Demonstrates pausing an entrypoint with LangGraph's `interrupt()` and waiting in
 Prerequisites: `uv sync --group langgraph` and a running Temporal dev server (`temporal server start-dev`).
 
 ```bash
-# Terminal 1
+# Terminal 1: start the worker
 uv run langgraph_plugin/functional_api/human_in_the_loop/run_worker.py
 
-# Terminal 2
+# Terminal 2: start the workflow (polls for the draft, then prompts you for feedback)
 uv run langgraph_plugin/functional_api/human_in_the_loop/run_workflow.py
 ```
 
+When the draft is ready, you'll be prompted at the terminal. Type `approve` to accept it as-is, or type revision feedback and the draft will be revised incorporating your notes.
+
 ## Files
 
 | File | Description |
 |------|-------------|
 | `workflow.py` | `@task` functions, `@entrypoint`, and `ChatbotFunctionalWorkflow` |
 | `run_worker.py` | Registers tasks and entrypoint with `LangGraphPlugin`, starts worker |
-| `run_workflow.py` | Starts workflow, polls draft via query, sends approval via signal |
+| `run_workflow.py` | Starts workflow, polls draft via query, prompts for human feedback, sends it via signal |

langgraph_plugin/functional_api/human_in_the_loop/run_workflow.py

@@ -28,8 +28,11 @@ async def main() -> None:
 
     print(f"Draft for review: {draft}")
 
-    # Send approval via signal
-    await handle.signal(ChatbotFunctionalWorkflow.provide_feedback, "approve")
+    # Prompt for human feedback instead of auto-approving.
+    feedback = await asyncio.to_thread(
+        input, "Enter 'approve' to accept, or type revision feedback: "
+    )
+    await handle.signal(ChatbotFunctionalWorkflow.provide_feedback, feedback)
 
     result = await handle.result()
     print(f"Final response: {result}")

langgraph_plugin/functional_api/human_in_the_loop/workflow.py

@@ -17,7 +17,7 @@
 
 
 @task
-def generate_draft(message: str) -> str:
+async def generate_draft(message: str) -> str:
     """Generate a draft response. Replace with an LLM call in production."""
     return (
         f"Here's my response to '{message}': "
@@ -26,16 +26,16 @@ def generate_draft(message: str) -> str:
 
 
 @task
-def request_human_review(draft: str) -> str:
-    """Pause execution to request human review of the draft."""
+async def request_human_review(draft: str) -> str:
+    """Present draft to human for review via interrupt; revise on feedback."""
     feedback = interrupt(draft)
     if feedback == "approve":
         return draft
     return f"[Revised] {draft} (incorporating feedback: {feedback})"
 
 
 @entrypoint()
-async def chatbot_entrypoint(user_message: str) -> dict:
+async def chatbot_entrypoint(user_message: str) -> dict[str, Any]:
     """Chatbot entrypoint: generate a draft, get human review, return result."""
     draft = await generate_draft(user_message)
     final_response = await request_human_review(draft)

langgraph_plugin/graph_api/human_in_the_loop/README.md

@@ -29,7 +29,7 @@ uv run langgraph_plugin/graph_api/human_in_the_loop/run_worker.py
 uv run langgraph_plugin/graph_api/human_in_the_loop/run_workflow.py
 ```
 
-When the draft is ready, you'll be prompted at the terminal. Type `approve` to accept it as-is, or type revision feedback and the draft will be regenerated by an LLM incorporating your notes.
+When the draft is ready, you'll be prompted at the terminal. Type `approve` to accept it as-is, or type revision feedback and the draft will be revised incorporating your notes.
 
 ## Files
 

langgraph_plugin/graph_api/human_in_the_loop/workflow.py

@@ -6,7 +6,6 @@
 
 from datetime import timedelta
 
-from langchain.chat_models import init_chat_model
 from langchain_core.runnables import RunnableConfig
 from langgraph.checkpoint.memory import InMemorySaver
 from langgraph.graph import START, StateGraph
@@ -21,25 +20,21 @@ class State(TypedDict):
 
 
 async def generate_draft(state: State) -> dict[str, str]:
-    """Generate a draft response with an LLM."""
-    response = await init_chat_model("claude-sonnet-4-6").ainvoke(
-        f"Please respond concisely to: {state['value']}"
-    )
-    return {"value": str(response.content)}
+    """Generate a draft response. Replace with an LLM call in production."""
+    return {
+        "value": (
+            f"Here's my response to '{state['value']}': "
+            "The answer is 42. Let me know if this helps!"
+        )
+    }
 
 
 async def human_review(state: State) -> dict[str, str]:
-    """Present draft to human for review via interrupt; revise with LLM on feedback."""
+    """Present draft to human for review via interrupt; revise on feedback."""
     feedback = interrupt(state["value"])
     if feedback == "approve":
         return {"value": state["value"]}
-    response = await init_chat_model("claude-sonnet-4-6").ainvoke(
-        "Revise the following draft according to the reviewer's feedback. "
-        "Output only the revised draft, with no preamble.\n\n"
-        f"Draft:\n{state['value']}\n\n"
-        f"Feedback:\n{feedback}"
-    )
-    return {"value": str(response.content)}
+    return {"value": f"[Revised] {state['value']} (incorporating feedback: {feedback})"}
 
 
 def make_chatbot_graph() -> StateGraph:

tests/langgraph_plugin/functional_human_in_the_loop_test.py

@@ -20,6 +20,16 @@
 )
 
 
+@pytest.fixture(autouse=True)
+def _restore_tasks():
+    original_funcs = [getattr(t, "func") for t in all_tasks]
+    try:
+        yield
+    finally:
+        for t, orig in zip(all_tasks, original_funcs):
+            setattr(t, "func", orig)
+
+
 async def test_functional_human_in_the_loop_approve(client: Client) -> None:
     task_queue = f"functional-hitl-test-{uuid.uuid4()}"
     plugin = LangGraphPlugin(
@@ -56,3 +66,43 @@ async def test_functional_human_in_the_loop_approve(client: Client) -> None:
         result = await handle.result()
 
     assert result["response"] == draft
+
+
+async def test_functional_human_in_the_loop_revise(client: Client) -> None:
+    task_queue = f"functional-hitl-revise-test-{uuid.uuid4()}"
+    plugin = LangGraphPlugin(
+        entrypoints={"chatbot": chatbot_entrypoint},
+        tasks=all_tasks,
+        activity_options=activity_options,
+    )
+
+    async with Worker(
+        client,
+        task_queue=task_queue,
+        workflows=[ChatbotFunctionalWorkflow],
+        plugins=[plugin],
+    ):
+        handle = await client.start_workflow(
+            ChatbotFunctionalWorkflow.run,
+            "test message",
+            id=f"functional-hitl-revise-{uuid.uuid4()}",
+            task_queue=task_queue,
+        )
+
+        # Poll for draft
+        draft = None
+        for _ in range(40):
+            await asyncio.sleep(0.25)
+            draft = await handle.query(ChatbotFunctionalWorkflow.get_draft)
+            if draft is not None:
+                break
+        assert draft is not None
+
+        # Send revision feedback
+        await handle.signal(
+            ChatbotFunctionalWorkflow.provide_feedback, "please be more concise"
+        )
+        result = await handle.result()
+
+    assert "[Revised]" in result["response"]
+    assert "please be more concise" in result["response"]

tests/langgraph_plugin/human_in_the_loop_test.py

@@ -1,7 +1,6 @@
 import asyncio
 import sys
 import uuid
-from unittest.mock import patch
 
 import pytest
 from temporalio.client import Client
@@ -19,59 +18,36 @@
 )
 
 
-class _FakeMessage:
-    def __init__(self, content: str) -> None:
-        self.content = content
-
-
-class _EchoModel:
-    """Stand-in for a chat model that echoes the prompt back as its response."""
-
-    async def ainvoke(self, prompt: str) -> _FakeMessage:
-        return _FakeMessage(prompt)
-
-
-def _fake_init_chat_model(*args: object, **kwargs: object) -> _EchoModel:
-    return _EchoModel()
-
-
-_patch_llm = lambda: patch(
-    "langgraph_plugin.graph_api.human_in_the_loop.workflow.init_chat_model",
-    _fake_init_chat_model,
-)
-
-
 async def test_human_in_the_loop_approve(client: Client) -> None:
     task_queue = f"hitl-test-{uuid.uuid4()}"
     plugin = LangGraphPlugin(graphs={"chatbot": make_chatbot_graph()})
 
-    with _patch_llm():
-        async with Worker(
-            client,
+    async with Worker(
+        client,
+        task_queue=task_queue,
+        workflows=[ChatbotWorkflow],
+        plugins=[plugin],
+    ):
+        handle = await client.start_workflow(
+            ChatbotWorkflow.run,
+            "test message",
+            id=f"hitl-{uuid.uuid4()}",
             task_queue=task_queue,
-            workflows=[ChatbotWorkflow],
-            plugins=[plugin],
-        ):
-            handle = await client.start_workflow(
-                ChatbotWorkflow.run,
-                "test message",
-                id=f"hitl-{uuid.uuid4()}",
-                task_queue=task_queue,
-            )
-
-            # Poll for draft to be ready
-            draft = None
-            for _ in range(40):
-                await asyncio.sleep(0.25)
-                draft = await handle.query(ChatbotWorkflow.get_draft)
-                if draft is not None:
-                    break
-            assert draft is not None
-            assert "test message" in draft
-
-            # Approve
-            await handle.signal(ChatbotWorkflow.provide_feedback, "approve")
-            result = await handle.result()
+        )
+
+        # Poll for draft to be ready
+        draft = None
+        for _ in range(40):
+            await asyncio.sleep(0.25)
+            draft = await handle.query(ChatbotWorkflow.get_draft)
+            if draft is not None:
+                break
+        assert draft is not None
+        assert "test message" in draft
+
+        # Approve
+        await handle.signal(ChatbotWorkflow.provide_feedback, "approve")
+        result = await handle.result()
 
     assert result == draft  # approved draft returned as-is
 
@@ -80,36 +56,31 @@ async def test_human_in_the_loop_revise(client: Client) -> None:
     task_queue = f"hitl-revise-test-{uuid.uuid4()}"
     plugin = LangGraphPlugin(graphs={"chatbot": make_chatbot_graph()})
 
-    with _patch_llm():
-        async with Worker(
-            client,
+    async with Worker(
+        client,
+        task_queue=task_queue,
+        workflows=[ChatbotWorkflow],
+        plugins=[plugin],
+    ):
+        handle = await client.start_workflow(
+            ChatbotWorkflow.run,
+            "test message",
+            id=f"hitl-revise-{uuid.uuid4()}",
             task_queue=task_queue,
-            workflows=[ChatbotWorkflow],
-            plugins=[plugin],
-        ):
-            handle = await client.start_workflow(
-                ChatbotWorkflow.run,
-                "test message",
-                id=f"hitl-revise-{uuid.uuid4()}",
-                task_queue=task_queue,
-            )
-
-            # Poll for draft
-            draft = None
-            for _ in range(40):
-                await asyncio.sleep(0.25)
-                draft = await handle.query(ChatbotWorkflow.get_draft)
-                if draft is not None:
-                    break
-            assert draft is not None
-
-            # Send revision feedback
-            await handle.signal(
-                ChatbotWorkflow.provide_feedback, "please be more concise"
-            )
-            result = await handle.result()
-
-    # The revision node feeds the draft and feedback into the LLM; the echo
-    # stand-in returns the revision prompt, which contains both.
+        )
+
+        # Poll for draft
+        draft = None
+        for _ in range(40):
+            await asyncio.sleep(0.25)
+            draft = await handle.query(ChatbotWorkflow.get_draft)
+            if draft is not None:
+                break
+        assert draft is not None
+
+        # Send revision feedback
+        await handle.signal(ChatbotWorkflow.provide_feedback, "please be more concise")
+        result = await handle.result()
+
+    assert "[Revised]" in result
     assert "please be more concise" in result
-    assert "test message" in result