feat: upgrade LangGraph to 1.x and migrate deprecated APIs

- Bump langgraph from 0.4 to 1.0+, langgraph-supervisor from 0.0.12 to 0.0.30+
- Bump langchain-core, langchain-anthropic, langchain-openai to 1.x
- Add langchain>=1.0 dependency for new create_agent location
- Migrate create_react_agent -> create_agent (prompt -> system_prompt)
- Fix create_supervisor positional arg to named agents= parameter
- Replace AsyncMock checkpointer with InMemorySaver in tests (v1 type validation)
- Update version references in README, ARCHITECTURE, eng-review-plan

backend/app/graph.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import logging
 from typing import TYPE_CHECKING
 
-from langgraph.prebuilt import create_react_agent
+from langchain.agents import create_agent
 from langgraph_supervisor import create_supervisor
 
 from app.agents import get_tools_by_names
@@ -59,11 +59,11 @@ def build_agent_nodes(
             f"Permission level: {agent_config.permission}."
         )
 
-        agent_node = create_react_agent(
+        agent_node = create_agent(
             model=llm,
             tools=tools,
             name=agent_config.name,
-            prompt=system_prompt,
+            system_prompt=system_prompt,
         )
         agent_nodes.append(agent_node)
 
@@ -88,7 +88,7 @@ def build_graph(
     prompt = SUPERVISOR_PROMPT.format(agent_descriptions=agent_descriptions)
 
     workflow = create_supervisor(
-        agent_nodes,
+        agents=agent_nodes,
         model=llm,
         prompt=prompt,
         output_mode="full_history",

backend/pyproject.toml

@@ -6,12 +6,13 @@ requires-python = ">=3.11"
 dependencies = [
     "fastapi>=0.115,<1.0",
     "uvicorn[standard]>=0.34,<1.0",
-    "langgraph>=0.4,<1.0",
-    "langgraph-supervisor>=0.0.12,<1.0",
+    "langgraph>=1.0,<2.0",
+    "langgraph-supervisor>=0.0.30,<1.0",
     "langgraph-checkpoint-postgres>=3.0,<4.0",
-    "langchain-core>=0.3,<1.0",
-    "langchain-anthropic>=0.3,<2.0",
-    "langchain-openai>=0.3,<1.0",
+    "langchain>=1.0,<2.0",
+    "langchain-core>=1.0,<2.0",
+    "langchain-anthropic>=1.0,<2.0",
+    "langchain-openai>=1.0,<2.0",
     "langchain-google-genai>=2.1,<3.0",
     "psycopg[binary,pool]>=3.2,<4.0",
     "pydantic>=2.10,<3.0",

backend/tests/unit/test_graph.py

@@ -6,6 +6,7 @@ from typing import TYPE_CHECKING
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
+from langgraph.checkpoint.memory import InMemorySaver
 
 from app.graph import build_agent_nodes, build_graph, classify_intent
 from app.intent import ClassificationResult, IntentTarget
@@ -34,20 +35,20 @@ class TestBuildGraph:
         mock_llm = MagicMock()
         mock_llm.bind_tools = MagicMock(return_value=mock_llm)
         mock_llm.with_structured_output = MagicMock(return_value=mock_llm)
-        mock_checkpointer = AsyncMock()
+        checkpointer = InMemorySaver()
 
-        graph = build_graph(sample_registry, mock_llm, mock_checkpointer)
+        graph = build_graph(sample_registry, mock_llm, checkpointer)
         assert graph is not None
 
     def test_graph_has_classifier_attached(self, sample_registry: AgentRegistry) -> None:
         mock_llm = MagicMock()
         mock_llm.bind_tools = MagicMock(return_value=mock_llm)
         mock_llm.with_structured_output = MagicMock(return_value=mock_llm)
-        mock_checkpointer = AsyncMock()
+        checkpointer = InMemorySaver()
         mock_classifier = MagicMock()
 
         graph = build_graph(
-            sample_registry, mock_llm, mock_checkpointer, intent_classifier=mock_classifier
+            sample_registry, mock_llm, checkpointer, intent_classifier=mock_classifier
         )
         assert graph.intent_classifier is mock_classifier
         assert graph.agent_registry is sample_registry
@@ -56,9 +57,9 @@ class TestBuildGraph:
         mock_llm = MagicMock()
         mock_llm.bind_tools = MagicMock(return_value=mock_llm)
         mock_llm.with_structured_output = MagicMock(return_value=mock_llm)
-        mock_checkpointer = AsyncMock()
+        checkpointer = InMemorySaver()
 
-        graph = build_graph(sample_registry, mock_llm, mock_checkpointer)
+        graph = build_graph(sample_registry, mock_llm, checkpointer)
         assert graph.intent_classifier is None