Support langgraph checkpointer (#1005)

* Add checkpointer configuration to config.example.yaml

- Introduced a new section for checkpointer configuration to enable state persistence for the embedded DeerFlowClient.
- Documented supported types: memory, sqlite, and postgres, along with examples for each.
- Clarified that the LangGraph Server manages its own state persistence separately.

* refactor(checkpointer): streamline checkpointer initialization and logging

* fix(uv.lock): update revision and add new wheel URLs for brotlicffi package

* feat: add langchain-anthropic dependency and update related configurations

* Fix checkpointer lifecycle, docstring, and path resolution bugs from PR #1005 review (#4)

* Initial plan

* Address all review suggestions from PR #1005

Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

* Fix resolve_path to always return real Path; move SQLite special-string handling to callers

Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

---------

Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

backend/langgraph.json

@@ -6,5 +6,8 @@
   "env": ".env",
   "graphs": {
     "lead_agent": "src.agents:make_lead_agent"
+  },
+  "checkpointer": {
+    "path": "./src/agents/checkpointer/async_provider.py:make_checkpointer"
   }
 }

backend/pyproject.toml

@@ -11,6 +11,7 @@ dependencies = [
     "httpx>=0.28.0",
     "kubernetes>=30.0.0",
     "langchain>=1.2.3",
+    "langchain-anthropic>=1.3.4",
     "langchain-deepseek>=1.0.1",
     "langchain-mcp-adapters>=0.1.0",
     "langchain-openai>=1.1.7",
@@ -32,6 +33,7 @@ dependencies = [
     "ddgs>=9.10.0",
     "duckdb>=1.4.4",
     "langchain-google-genai>=4.2.1",
+    "langgraph-checkpoint-sqlite>=3.0.3",
 ]
 
 [dependency-groups]

backend/src/agents/__init__.py

@@ -1,4 +1,5 @@
+from .checkpointer import get_checkpointer, make_checkpointer, reset_checkpointer
 from .lead_agent import make_lead_agent
 from .thread_state import SandboxState, ThreadState
 
-__all__ = ["make_lead_agent", "SandboxState", "ThreadState"]
+__all__ = ["make_lead_agent", "SandboxState", "ThreadState", "get_checkpointer", "reset_checkpointer", "make_checkpointer"]

backend/src/agents/checkpointer/__init__.py

@@ -0,0 +1,9 @@
+from .async_provider import make_checkpointer
+from .provider import checkpointer_context, get_checkpointer, reset_checkpointer
+
+__all__ = [
+    "get_checkpointer",
+    "reset_checkpointer",
+    "checkpointer_context",
+    "make_checkpointer",
+]

backend/src/agents/checkpointer/async_provider.py

@@ -0,0 +1,107 @@
+"""Async checkpointer factory.
+
+Provides an **async context manager** for long-running async servers that need
+proper resource cleanup.
+
+Supported backends: memory, sqlite, postgres.
+
+Usage (e.g. FastAPI lifespan)::
+
+    from src.agents.checkpointer.async_provider import make_checkpointer
+
+    async with make_checkpointer() as checkpointer:
+        app.state.checkpointer = checkpointer  # None if not configured
+
+For sync usage see :mod:`src.agents.checkpointer.provider`.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import logging
+from collections.abc import AsyncIterator
+
+from langgraph.types import Checkpointer
+
+from src.agents.checkpointer.provider import (
+    POSTGRES_CONN_REQUIRED,
+    POSTGRES_INSTALL,
+    SQLITE_INSTALL,
+    _resolve_sqlite_conn_str,
+)
+from src.config.app_config import get_app_config
+
+logger = logging.getLogger(__name__)
+
+# ---------------------------------------------------------------------------
+# Async factory
+# ---------------------------------------------------------------------------
+
+
+@contextlib.asynccontextmanager
+async def _async_checkpointer(config) -> AsyncIterator[Checkpointer]:
+    """Async context manager that constructs and tears down a checkpointer."""
+    if config.type == "memory":
+        from langgraph.checkpoint.memory import InMemorySaver
+
+        yield InMemorySaver()
+        return
+
+    if config.type == "sqlite":
+        try:
+            from langgraph.checkpoint.sqlite.aio import AsyncSqliteSaver
+        except ImportError as exc:
+            raise ImportError(SQLITE_INSTALL) from exc
+
+        import pathlib
+
+        conn_str = _resolve_sqlite_conn_str(config.connection_string or "store.db")
+        # Only create parent directories for real filesystem paths
+        if conn_str != ":memory:" and not conn_str.startswith("file:"):
+            pathlib.Path(conn_str).parent.mkdir(parents=True, exist_ok=True)
+        async with AsyncSqliteSaver.from_conn_string(conn_str) as saver:
+            await saver.setup()
+            yield saver
+        return
+
+    if config.type == "postgres":
+        try:
+            from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
+        except ImportError as exc:
+            raise ImportError(POSTGRES_INSTALL) from exc
+
+        if not config.connection_string:
+            raise ValueError(POSTGRES_CONN_REQUIRED)
+
+        async with AsyncPostgresSaver.from_conn_string(config.connection_string) as saver:
+            await saver.setup()
+            yield saver
+        return
+
+    raise ValueError(f"Unknown checkpointer type: {config.type!r}")
+
+
+# ---------------------------------------------------------------------------
+# Public async context manager
+# ---------------------------------------------------------------------------
+
+
+@contextlib.asynccontextmanager
+async def make_checkpointer() -> AsyncIterator[Checkpointer | None]:
+    """Async context manager that yields a checkpointer for the caller's lifetime.
+    Resources are opened on enter and closed on exit — no global state::
+
+        async with make_checkpointer() as checkpointer:
+            app.state.checkpointer = checkpointer
+
+    Yields ``None`` when no checkpointer is configured in *config.yaml*.
+    """
+
+    config = get_app_config()
+
+    if config.checkpointer is None:
+        yield None
+        return
+
+    async with _async_checkpointer(config.checkpointer) as saver:
+        yield saver

backend/src/agents/checkpointer/provider.py

@@ -0,0 +1,179 @@
+"""Sync checkpointer factory.
+
+Provides a **sync singleton** and a **sync context manager** for LangGraph
+graph compilation and CLI tools.
+
+Supported backends: memory, sqlite, postgres.
+
+Usage::
+
+    from src.agents.checkpointer.provider import get_checkpointer, checkpointer_context
+
+    # Singleton — reused across calls, closed on process exit
+    cp = get_checkpointer()
+
+    # One-shot — fresh connection, closed on block exit
+    with checkpointer_context() as cp:
+        graph.invoke(input, config={"configurable": {"thread_id": "1"}})
+"""
+
+from __future__ import annotations
+
+import contextlib
+import logging
+from collections.abc import Iterator
+
+from langgraph.types import Checkpointer
+
+from src.config.app_config import get_app_config
+from src.config.checkpointer_config import CheckpointerConfig
+from src.config.paths import resolve_path
+
+logger = logging.getLogger(__name__)
+
+# ---------------------------------------------------------------------------
+# Error message constants — imported by aio.provider too
+# ---------------------------------------------------------------------------
+
+SQLITE_INSTALL = "langgraph-checkpoint-sqlite is required for the SQLite checkpointer. Install it with: uv add langgraph-checkpoint-sqlite"
+POSTGRES_INSTALL = "langgraph-checkpoint-postgres is required for the PostgreSQL checkpointer. Install it with: uv add langgraph-checkpoint-postgres psycopg[binary] psycopg-pool"
+POSTGRES_CONN_REQUIRED = "checkpointer.connection_string is required for the postgres backend"
+
+# ---------------------------------------------------------------------------
+# Sync factory
+# ---------------------------------------------------------------------------
+
+
+def _resolve_sqlite_conn_str(raw: str) -> str:
+    """Return a SQLite connection string ready for use with ``SqliteSaver``.
+
+    SQLite special strings (``":memory:"`` and ``file:`` URIs) are returned
+    unchanged.  Plain filesystem paths — relative or absolute — are resolved
+    to an absolute string via :func:`resolve_path`.
+    """
+    if raw == ":memory:" or raw.startswith("file:"):
+        return raw
+    return str(resolve_path(raw))
+
+
+@contextlib.contextmanager
+def _sync_checkpointer_cm(config: CheckpointerConfig) -> Iterator[Checkpointer]:
+    """Context manager that creates and tears down a sync checkpointer.
+
+    Returns a configured ``Checkpointer`` instance. Resource cleanup for any
+    underlying connections or pools is handled by higher-level helpers in
+    this module (such as the singleton factory or context manager); this
+    function does not return a separate cleanup callback.
+    """
+    if config.type == "memory":
+        from langgraph.checkpoint.memory import InMemorySaver
+
+        logger.info("Checkpointer: using InMemorySaver (in-process, not persistent)")
+        yield InMemorySaver()
+        return
+
+    if config.type == "sqlite":
+        try:
+            from langgraph.checkpoint.sqlite import SqliteSaver
+        except ImportError as exc:
+            raise ImportError(SQLITE_INSTALL) from exc
+
+        conn_str = _resolve_sqlite_conn_str(config.connection_string or "store.db")
+        with SqliteSaver.from_conn_string(conn_str) as saver:
+            saver.setup()
+            logger.info("Checkpointer: using SqliteSaver (%s)", conn_str)
+            yield saver
+        return
+
+    if config.type == "postgres":
+        try:
+            from langgraph.checkpoint.postgres import PostgresSaver
+        except ImportError as exc:
+            raise ImportError(POSTGRES_INSTALL) from exc
+
+        if not config.connection_string:
+            raise ValueError(POSTGRES_CONN_REQUIRED)
+
+        with PostgresSaver.from_conn_string(config.connection_string) as saver:
+            saver.setup()
+            logger.info("Checkpointer: using PostgresSaver")
+            yield saver
+        return
+
+    raise ValueError(f"Unknown checkpointer type: {config.type!r}")
+
+
+# ---------------------------------------------------------------------------
+# Sync singleton
+# ---------------------------------------------------------------------------
+
+_checkpointer: Checkpointer = None
+_checkpointer_ctx = None  # open context manager keeping the connection alive
+
+
+def get_checkpointer() -> Checkpointer | None:
+    """Return the global sync checkpointer singleton, creating it on first call.
+
+    Returns ``None`` when no checkpointer is configured in *config.yaml*.
+
+    Raises:
+        ImportError: If the required package for the configured backend is not installed.
+        ValueError: If ``connection_string`` is missing for a backend that requires it.
+    """
+    global _checkpointer, _checkpointer_ctx
+
+    if _checkpointer is not None:
+        return _checkpointer
+
+    from src.config.checkpointer_config import get_checkpointer_config
+
+    config = get_checkpointer_config()
+    if config is None:
+        return None
+
+    _checkpointer_ctx = _sync_checkpointer_cm(config)
+    _checkpointer = _checkpointer_ctx.__enter__()
+
+    return _checkpointer
+
+
+def reset_checkpointer() -> None:
+    """Reset the sync singleton, forcing recreation on the next call.
+
+    Closes any open backend connections and clears the cached instance.
+    Useful in tests or after a configuration change.
+    """
+    global _checkpointer, _checkpointer_ctx
+    if _checkpointer_ctx is not None:
+        try:
+            _checkpointer_ctx.__exit__(None, None, None)
+        except Exception:
+            logger.warning("Error during checkpointer cleanup", exc_info=True)
+        _checkpointer_ctx = None
+    _checkpointer = None
+
+
+# ---------------------------------------------------------------------------
+# Sync context manager
+# ---------------------------------------------------------------------------
+
+
+@contextlib.contextmanager
+def checkpointer_context() -> Iterator[Checkpointer | None]:
+    """Sync context manager that yields a checkpointer and cleans up on exit.
+
+    Unlike :func:`get_checkpointer`, this does **not** cache the instance —
+    each ``with`` block creates and destroys its own connection.  Use it in
+    CLI scripts or tests where you want deterministic cleanup::
+
+        with checkpointer_context() as cp:
+            graph.invoke(input, config={"configurable": {"thread_id": "1"}})
+    """
+
+    config = get_app_config()
+    if config.checkpointer is None:
+        yield None
+        return
+
+    with _sync_checkpointer_cm(config.checkpointer) as saver:
+        yield saver

backend/src/client.py

@@ -152,7 +152,10 @@ class DeerFlowClient:
     def _atomic_write_json(path: Path, data: dict) -> None:
         """Write JSON to *path* atomically (temp file + replace)."""
         fd = tempfile.NamedTemporaryFile(
-            mode="w", dir=path.parent, suffix=".tmp", delete=False,
+            mode="w",
+            dir=path.parent,
+            suffix=".tmp",
+            delete=False,
         )
         try:
             json.dump(data, fd, indent=2)
@@ -205,8 +208,13 @@ class DeerFlowClient:
             ),
             "state_schema": ThreadState,
         }
-        if self._checkpointer is not None:
+        checkpointer = self._checkpointer
-            kwargs["checkpointer"] = self._checkpointer
+        if checkpointer is None:
+            from src.agents.checkpointer import get_checkpointer
+
+            checkpointer = get_checkpointer()
+        if checkpointer is not None:
+            kwargs["checkpointer"] = checkpointer
 
         self._agent = create_agent(**kwargs)
         self._agent_config_key = key
@@ -320,10 +328,7 @@ class DeerFlowClient:
                                 "type": "ai",
                                 "content": "",
                                 "id": msg_id,
-                                "tool_calls": [
+                                "tool_calls": [{"name": tc["name"], "args": tc["args"], "id": tc.get("id")} for tc in msg.tool_calls],
-                                    {"name": tc["name"], "args": tc["args"], "id": tc.get("id")}
-                                    for tc in msg.tool_calls
-                                ],
                             },
                         )
 
@@ -494,10 +499,7 @@ class DeerFlowClient:
         """
         config_path = ExtensionsConfig.resolve_config_path()
         if config_path is None:
-            raise FileNotFoundError(
+            raise FileNotFoundError("Cannot locate extensions_config.json. Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root.")
-                "Cannot locate extensions_config.json. "
-                "Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root."
-            )
 
         current_config = get_extensions_config()
 
@@ -561,10 +563,7 @@ class DeerFlowClient:
 
         config_path = ExtensionsConfig.resolve_config_path()
         if config_path is None:
-            raise FileNotFoundError(
+            raise FileNotFoundError("Cannot locate extensions_config.json. Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root.")
-                "Cannot locate extensions_config.json. "
-                "Set DEER_FLOW_EXTENSIONS_CONFIG_PATH or ensure it exists in the project root."
-            )
 
         extensions_config = get_extensions_config()
         extensions_config.skills[name] = SkillStateConfig(enabled=enabled)
@@ -739,7 +738,6 @@ class DeerFlowClient:
         uploaded_files: list[dict] = []
 
         for src_path in resolved_files:
-
             dest = uploads_dir / src_path.name
             shutil.copy2(src_path, dest)
 
@@ -756,6 +754,7 @@ class DeerFlowClient:
                     try:
                         asyncio.get_running_loop()
                         import concurrent.futures
+
                         with concurrent.futures.ThreadPoolExecutor() as pool:
                             md_path = pool.submit(lambda: asyncio.run(convert_file_to_markdown(dest))).result()
                     except RuntimeError:
@@ -795,15 +794,17 @@ class DeerFlowClient:
         for fp in sorted(uploads_dir.iterdir()):
             if fp.is_file():
                 stat = fp.stat()
-                files.append({
+                files.append(
-                    "filename": fp.name,
+                    {
-                    "size": str(stat.st_size),
+                        "filename": fp.name,
-                    "path": str(fp),
+                        "size": str(stat.st_size),
-                    "virtual_path": f"/mnt/user-data/uploads/{fp.name}",
+                        "path": str(fp),
-                    "artifact_url": f"/api/threads/{thread_id}/artifacts/mnt/user-data/uploads/{fp.name}",
+                        "virtual_path": f"/mnt/user-data/uploads/{fp.name}",
-                    "extension": fp.suffix,
+                        "artifact_url": f"/api/threads/{thread_id}/artifacts/mnt/user-data/uploads/{fp.name}",
-                    "modified": stat.st_mtime,
+                        "extension": fp.suffix,
-                })
+                        "modified": stat.st_mtime,
+                    }
+                )
         return {"files": files, "count": len(files)}
 
     def delete_upload(self, thread_id: str, filename: str) -> dict:
@@ -858,7 +859,7 @@ class DeerFlowClient:
         if not clean_path.startswith(virtual_prefix):
             raise ValueError(f"Path must start with /{virtual_prefix}")
 
-        relative = clean_path[len(virtual_prefix):].lstrip("/")
+        relative = clean_path[len(virtual_prefix) :].lstrip("/")
         base_dir = get_paths().sandbox_user_data_dir(thread_id)
         actual = (base_dir / relative).resolve()
 

backend/src/config/app_config.py

@@ -6,6 +6,7 @@ import yaml
 from dotenv import load_dotenv
 from pydantic import BaseModel, ConfigDict, Field
 
+from src.config.checkpointer_config import CheckpointerConfig, load_checkpointer_config_from_dict
 from src.config.extensions_config import ExtensionsConfig
 from src.config.memory_config import load_memory_config_from_dict
 from src.config.model_config import ModelConfig
@@ -29,6 +30,7 @@ class AppConfig(BaseModel):
     skills: SkillsConfig = Field(default_factory=SkillsConfig, description="Skills configuration")
     extensions: ExtensionsConfig = Field(default_factory=ExtensionsConfig, description="Extensions configuration (MCP servers and skills state)")
     model_config = ConfigDict(extra="allow", frozen=False)
+    checkpointer: CheckpointerConfig | None = Field(default=None, description="Checkpointer configuration")
 
     @classmethod
     def resolve_config_path(cls, config_path: str | None = None) -> Path:
@@ -92,6 +94,10 @@ class AppConfig(BaseModel):
         if "subagents" in config_data:
             load_subagents_config_from_dict(config_data["subagents"])
 
+        # Load checkpointer config if present
+        if "checkpointer" in config_data:
+            load_checkpointer_config_from_dict(config_data["checkpointer"])
+
         # Load extensions config separately (it's in a different file)
         extensions_config = ExtensionsConfig.from_file()
         config_data["extensions"] = extensions_config.model_dump()

backend/src/config/checkpointer_config.py

@@ -0,0 +1,46 @@
+"""Configuration for LangGraph checkpointer."""
+
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+CheckpointerType = Literal["memory", "sqlite", "postgres"]
+
+
+class CheckpointerConfig(BaseModel):
+    """Configuration for LangGraph state persistence checkpointer."""
+
+    type: CheckpointerType = Field(
+        description="Checkpointer backend type. "
+        "'memory' is in-process only (lost on restart). "
+        "'sqlite' persists to a local file (requires langgraph-checkpoint-sqlite). "
+        "'postgres' persists to PostgreSQL (requires langgraph-checkpoint-postgres)."
+    )
+    connection_string: str | None = Field(
+        default=None,
+        description="Connection string for sqlite (file path) or postgres (DSN). "
+        "Required for sqlite and postgres types. "
+        "For sqlite, use a file path like '.deer-flow/checkpoints.db' or ':memory:' for in-memory. "
+        "For postgres, use a DSN like 'postgresql://user:pass@localhost:5432/db'.",
+    )
+
+
+# Global configuration instance — None means no checkpointer is configured.
+_checkpointer_config: CheckpointerConfig | None = None
+
+
+def get_checkpointer_config() -> CheckpointerConfig | None:
+    """Get the current checkpointer configuration, or None if not configured."""
+    return _checkpointer_config
+
+
+def set_checkpointer_config(config: CheckpointerConfig | None) -> None:
+    """Set the checkpointer configuration."""
+    global _checkpointer_config
+    _checkpointer_config = config
+
+
+def load_checkpointer_config_from_dict(config_dict: dict) -> None:
+    """Load checkpointer configuration from a dictionary."""
+    global _checkpointer_config
+    _checkpointer_config = CheckpointerConfig(**config_dict)

backend/src/config/paths.py

@@ -176,3 +176,15 @@ def get_paths() -> Paths:
     if _paths is None:
         _paths = Paths()
     return _paths
+
+
+def resolve_path(path: str) -> Path:
+    """Resolve *path* to an absolute ``Path``.
+
+    Relative paths are resolved relative to the application base directory.
+    Absolute paths are returned as-is (after normalisation).
+    """
+    p = Path(path)
+    if not p.is_absolute():
+        p = get_paths().base_dir / path
+    return p.resolve()

backend/tests/test_checkpointer.py

@@ -0,0 +1,255 @@
+"""Unit tests for checkpointer config and singleton factory."""
+
+import sys
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from src.agents.checkpointer import get_checkpointer, reset_checkpointer
+from src.config.checkpointer_config import (
+    CheckpointerConfig,
+    get_checkpointer_config,
+    load_checkpointer_config_from_dict,
+    set_checkpointer_config,
+)
+
+
+@pytest.fixture(autouse=True)
+def reset_state():
+    """Reset singleton state before each test."""
+    set_checkpointer_config(None)
+    reset_checkpointer()
+    yield
+    set_checkpointer_config(None)
+    reset_checkpointer()
+
+
+# ---------------------------------------------------------------------------
+# Config tests
+# ---------------------------------------------------------------------------
+
+
+class TestCheckpointerConfig:
+    def test_load_memory_config(self):
+        load_checkpointer_config_from_dict({"type": "memory"})
+        config = get_checkpointer_config()
+        assert config is not None
+        assert config.type == "memory"
+        assert config.connection_string is None
+
+    def test_load_sqlite_config(self):
+        load_checkpointer_config_from_dict({"type": "sqlite", "connection_string": "/tmp/test.db"})
+        config = get_checkpointer_config()
+        assert config is not None
+        assert config.type == "sqlite"
+        assert config.connection_string == "/tmp/test.db"
+
+    def test_load_postgres_config(self):
+        load_checkpointer_config_from_dict({"type": "postgres", "connection_string": "postgresql://localhost/db"})
+        config = get_checkpointer_config()
+        assert config is not None
+        assert config.type == "postgres"
+        assert config.connection_string == "postgresql://localhost/db"
+
+    def test_default_connection_string_is_none(self):
+        config = CheckpointerConfig(type="memory")
+        assert config.connection_string is None
+
+    def test_set_config_to_none(self):
+        load_checkpointer_config_from_dict({"type": "memory"})
+        set_checkpointer_config(None)
+        assert get_checkpointer_config() is None
+
+    def test_invalid_type_raises(self):
+        with pytest.raises(Exception):
+            load_checkpointer_config_from_dict({"type": "unknown"})
+
+
+# ---------------------------------------------------------------------------
+# Factory tests
+# ---------------------------------------------------------------------------
+
+
+class TestGetCheckpointer:
+    def test_returns_none_when_not_configured(self):
+        assert get_checkpointer() is None
+
+    def test_memory_returns_in_memory_saver(self):
+        load_checkpointer_config_from_dict({"type": "memory"})
+        from langgraph.checkpoint.memory import InMemorySaver
+
+        cp = get_checkpointer()
+        assert isinstance(cp, InMemorySaver)
+
+    def test_memory_singleton(self):
+        load_checkpointer_config_from_dict({"type": "memory"})
+        cp1 = get_checkpointer()
+        cp2 = get_checkpointer()
+        assert cp1 is cp2
+
+    def test_reset_clears_singleton(self):
+        load_checkpointer_config_from_dict({"type": "memory"})
+        cp1 = get_checkpointer()
+        reset_checkpointer()
+        cp2 = get_checkpointer()
+        assert cp1 is not cp2
+
+    def test_sqlite_raises_when_package_missing(self):
+        load_checkpointer_config_from_dict({"type": "sqlite", "connection_string": "/tmp/test.db"})
+        with patch.dict(sys.modules, {"langgraph.checkpoint.sqlite": None}):
+            reset_checkpointer()
+            with pytest.raises(ImportError, match="langgraph-checkpoint-sqlite"):
+                get_checkpointer()
+
+    def test_postgres_raises_when_package_missing(self):
+        load_checkpointer_config_from_dict({"type": "postgres", "connection_string": "postgresql://localhost/db"})
+        with patch.dict(sys.modules, {"langgraph.checkpoint.postgres": None}):
+            reset_checkpointer()
+            with pytest.raises(ImportError, match="langgraph-checkpoint-postgres"):
+                get_checkpointer()
+
+    def test_postgres_raises_when_connection_string_missing(self):
+        load_checkpointer_config_from_dict({"type": "postgres"})
+        mock_saver = MagicMock()
+        mock_module = MagicMock()
+        mock_module.PostgresSaver = mock_saver
+        with patch.dict(sys.modules, {"langgraph.checkpoint.postgres": mock_module}):
+            reset_checkpointer()
+            with pytest.raises(ValueError, match="connection_string is required"):
+                get_checkpointer()
+
+    def test_sqlite_creates_saver(self):
+        """SQLite checkpointer is created when package is available."""
+        load_checkpointer_config_from_dict({"type": "sqlite", "connection_string": "/tmp/test.db"})
+
+        mock_saver_instance = MagicMock()
+        mock_cm = MagicMock()
+        mock_cm.__enter__ = MagicMock(return_value=mock_saver_instance)
+        mock_cm.__exit__ = MagicMock(return_value=False)
+
+        mock_saver_cls = MagicMock()
+        mock_saver_cls.from_conn_string = MagicMock(return_value=mock_cm)
+
+        mock_module = MagicMock()
+        mock_module.SqliteSaver = mock_saver_cls
+
+        with patch.dict(sys.modules, {"langgraph.checkpoint.sqlite": mock_module}):
+            reset_checkpointer()
+            cp = get_checkpointer()
+
+        assert cp is mock_saver_instance
+        mock_saver_cls.from_conn_string.assert_called_once()
+        mock_saver_instance.setup.assert_called_once()
+
+    def test_postgres_creates_saver(self):
+        """Postgres checkpointer is created when packages are available."""
+        load_checkpointer_config_from_dict({"type": "postgres", "connection_string": "postgresql://localhost/db"})
+
+        mock_saver_instance = MagicMock()
+        mock_cm = MagicMock()
+        mock_cm.__enter__ = MagicMock(return_value=mock_saver_instance)
+        mock_cm.__exit__ = MagicMock(return_value=False)
+
+        mock_saver_cls = MagicMock()
+        mock_saver_cls.from_conn_string = MagicMock(return_value=mock_cm)
+
+        mock_pg_module = MagicMock()
+        mock_pg_module.PostgresSaver = mock_saver_cls
+
+        with patch.dict(sys.modules, {"langgraph.checkpoint.postgres": mock_pg_module}):
+            reset_checkpointer()
+            cp = get_checkpointer()
+
+        assert cp is mock_saver_instance
+        mock_saver_cls.from_conn_string.assert_called_once_with("postgresql://localhost/db")
+        mock_saver_instance.setup.assert_called_once()
+
+
+# ---------------------------------------------------------------------------
+# app_config.py integration
+# ---------------------------------------------------------------------------
+
+
+class TestAppConfigLoadsCheckpointer:
+    def test_load_checkpointer_section(self):
+        """load_checkpointer_config_from_dict populates the global config."""
+        set_checkpointer_config(None)
+        load_checkpointer_config_from_dict({"type": "memory"})
+        cfg = get_checkpointer_config()
+        assert cfg is not None
+        assert cfg.type == "memory"
+
+
+# ---------------------------------------------------------------------------
+# DeerFlowClient falls back to config checkpointer
+# ---------------------------------------------------------------------------
+
+
+class TestClientCheckpointerFallback:
+    def test_client_uses_config_checkpointer_when_none_provided(self):
+        """DeerFlowClient._ensure_agent falls back to get_checkpointer() when checkpointer=None."""
+        from langgraph.checkpoint.memory import InMemorySaver
+
+        from src.client import DeerFlowClient
+
+        load_checkpointer_config_from_dict({"type": "memory"})
+
+        captured_kwargs = {}
+
+        def fake_create_agent(**kwargs):
+            captured_kwargs.update(kwargs)
+            return MagicMock()
+
+        model_mock = MagicMock()
+        config_mock = MagicMock()
+        config_mock.models = [model_mock]
+        config_mock.get_model_config.return_value = MagicMock(supports_vision=False)
+        config_mock.checkpointer = None
+
+        with (
+            patch("src.client.get_app_config", return_value=config_mock),
+            patch("src.client.create_agent", side_effect=fake_create_agent),
+            patch("src.client.create_chat_model", return_value=MagicMock()),
+            patch("src.client._build_middlewares", return_value=[]),
+            patch("src.client.apply_prompt_template", return_value=""),
+            patch("src.client.DeerFlowClient._get_tools", return_value=[]),
+        ):
+            client = DeerFlowClient(checkpointer=None)
+            config = client._get_runnable_config("test-thread")
+            client._ensure_agent(config)
+
+        assert "checkpointer" in captured_kwargs
+        assert isinstance(captured_kwargs["checkpointer"], InMemorySaver)
+
+    def test_client_explicit_checkpointer_takes_precedence(self):
+        """An explicitly provided checkpointer is used even when config checkpointer is set."""
+        from src.client import DeerFlowClient
+
+        load_checkpointer_config_from_dict({"type": "memory"})
+
+        explicit_cp = MagicMock()
+        captured_kwargs = {}
+
+        def fake_create_agent(**kwargs):
+            captured_kwargs.update(kwargs)
+            return MagicMock()
+
+        model_mock = MagicMock()
+        config_mock = MagicMock()
+        config_mock.models = [model_mock]
+        config_mock.get_model_config.return_value = MagicMock(supports_vision=False)
+        config_mock.checkpointer = None
+
+        with (
+            patch("src.client.get_app_config", return_value=config_mock),
+            patch("src.client.create_agent", side_effect=fake_create_agent),
+            patch("src.client.create_chat_model", return_value=MagicMock()),
+            patch("src.client._build_middlewares", return_value=[]),
+            patch("src.client.apply_prompt_template", return_value=""),
+            patch("src.client.DeerFlowClient._get_tools", return_value=[]),
+        ):
+            client = DeerFlowClient(checkpointer=explicit_cp)
+            config = client._get_runnable_config("test-thread")
+            client._ensure_agent(config)
+
+        assert captured_kwargs["checkpointer"] is explicit_cp

backend/tests/test_client_live.py

@@ -28,6 +28,7 @@ if _skip_reason:
 # Fixtures
 # ---------------------------------------------------------------------------
 
+
 @pytest.fixture(scope="module")
 def client():
     """Create a real DeerFlowClient (no mocks)."""
@@ -38,6 +39,7 @@ def client():
 def thread_tmp(tmp_path):
     """Provide a unique thread_id + tmp directory for file operations."""
     import uuid
+
     tid = f"live-test-{uuid.uuid4().hex[:8]}"
     return tid, tmp_path
 
@@ -46,6 +48,7 @@ def thread_tmp(tmp_path):
 # Scenario 1: Basic chat — model responds coherently
 # ===========================================================================
 
+
 class TestLiveBasicChat:
     def test_chat_returns_nonempty_string(self, client):
         """chat() returns a non-empty response from the real model."""
@@ -65,6 +68,7 @@ class TestLiveBasicChat:
 # Scenario 2: Streaming — events arrive in correct order
 # ===========================================================================
 
+
 class TestLiveStreaming:
     def test_stream_yields_messages_tuple_and_end(self, client):
         """stream() produces at least one messages-tuple event and ends with end."""
@@ -81,10 +85,7 @@ class TestLiveStreaming:
 
     def test_stream_ai_content_nonempty(self, client):
         """Streamed messages-tuple AI events contain non-empty content."""
-        ai_messages = [
+        ai_messages = [e for e in client.stream("What color is the sky? One word.") if e.type == "messages-tuple" and e.data.get("type") == "ai" and e.data.get("content")]
-            e for e in client.stream("What color is the sky? One word.")
-            if e.type == "messages-tuple" and e.data.get("type") == "ai" and e.data.get("content")
-        ]
         assert len(ai_messages) >= 1
         for m in ai_messages:
             assert len(m.data.get("content", "")) > 0
@@ -94,13 +95,11 @@ class TestLiveStreaming:
 # Scenario 3: Tool use — agent calls a tool and returns result
 # ===========================================================================
 
+
 class TestLiveToolUse:
     def test_agent_uses_bash_tool(self, client):
         """Agent uses bash tool when asked to run a command."""
-        events = list(client.stream(
+        events = list(client.stream("Use the bash tool to run: echo 'LIVE_TEST_OK'. Then tell me the output."))
-            "Use the bash tool to run: echo 'LIVE_TEST_OK'. "
-            "Then tell me the output."
-        ))
 
         types = [e.type for e in events]
         print(f"  event types: {types}")
@@ -122,10 +121,7 @@ class TestLiveToolUse:
 
     def test_agent_uses_ls_tool(self, client):
         """Agent uses ls tool to list a directory."""
-        events = list(client.stream(
+        events = list(client.stream("Use the ls tool to list the contents of /mnt/user-data/workspace. Just report what you see."))
-            "Use the ls tool to list the contents of /mnt/user-data/workspace. "
-            "Just report what you see."
-        ))
 
         types = [e.type for e in events]
         print(f"  event types: {types}")
@@ -139,15 +135,11 @@ class TestLiveToolUse:
 # Scenario 4: Multi-tool chain — agent chains tools in sequence
 # ===========================================================================
 
+
 class TestLiveMultiToolChain:
     def test_write_then_read(self, client):
         """Agent writes a file, then reads it back."""
-        events = list(client.stream(
+        events = list(client.stream("Step 1: Use write_file to write 'integration_test_content' to /mnt/user-data/outputs/live_test.txt. Step 2: Use read_file to read that file back. Step 3: Tell me the content you read."))
-            "Step 1: Use write_file to write 'integration_test_content' to "
-            "/mnt/user-data/outputs/live_test.txt. "
-            "Step 2: Use read_file to read that file back. "
-            "Step 3: Tell me the content you read."
-        ))
 
         types = [e.type for e in events]
         print(f"  event types: {types}")
@@ -164,16 +156,14 @@ class TestLiveMultiToolChain:
         ai_events = [e for e in events if e.type == "messages-tuple" and e.data.get("type") == "ai" and e.data.get("content")]
         tr_events = [e for e in events if e.type == "messages-tuple" and e.data.get("type") == "tool"]
         final_text = ai_events[-1].data["content"] if ai_events else ""
-        assert "integration_test_content" in final_text.lower() or any(
+        assert "integration_test_content" in final_text.lower() or any("integration_test_content" in e.data.get("content", "") for e in tr_events)
-            "integration_test_content" in e.data.get("content", "")
-            for e in tr_events
-        )
 
 
 # ===========================================================================
 # Scenario 5: File upload lifecycle with real filesystem
 # ===========================================================================
 
+
 class TestLiveFileUpload:
     def test_upload_list_delete(self, client, thread_tmp):
         """Upload → list → delete → verify deletion."""
@@ -225,6 +215,7 @@ class TestLiveFileUpload:
 # Scenario 6: Configuration query — real config loading
 # ===========================================================================
 
+
 class TestLiveConfigQueries:
     def test_list_models_returns_configured_model(self, client):
         """list_models() returns at least one configured model with Gateway-aligned fields."""
@@ -266,25 +257,25 @@ class TestLiveConfigQueries:
 # Scenario 7: Artifact read after agent writes
 # ===========================================================================
 
+
 class TestLiveArtifact:
     def test_get_artifact_after_write(self, client):
         """Agent writes a file → client reads it back via get_artifact()."""
         import uuid
+
         thread_id = f"live-artifact-{uuid.uuid4().hex[:8]}"
 
         # Ask agent to write a file
-        events = list(client.stream(
+        events = list(
-            "Use write_file to create /mnt/user-data/outputs/artifact_test.json "
+            client.stream(
-            "with content: {\"status\": \"ok\", \"source\": \"live_test\"}",
+                'Use write_file to create /mnt/user-data/outputs/artifact_test.json with content: {"status": "ok", "source": "live_test"}',
-            thread_id=thread_id,
+                thread_id=thread_id,
-        ))
+            )
+        )
 
         # Verify write happened
         tc_events = [e for e in events if e.type == "messages-tuple" and e.data.get("type") == "ai" and "tool_calls" in e.data]
-        assert any(
+        assert any(any(tc["name"] == "write_file" for tc in e.data["tool_calls"]) for e in tc_events)
-            any(tc["name"] == "write_file" for tc in e.data["tool_calls"])
-            for e in tc_events
-        )
 
         # Read artifact
         content, mime = client.get_artifact(thread_id, "mnt/user-data/outputs/artifact_test.json")
@@ -303,11 +294,13 @@ class TestLiveArtifact:
 # Scenario 8: Per-call overrides
 # ===========================================================================
 
+
 class TestLiveOverrides:
     def test_thinking_disabled_still_works(self, client):
         """Explicit thinking_enabled=False override produces a response."""
         response = client.chat(
-            "Say OK.", thinking_enabled=False,
+            "Say OK.",
+            thinking_enabled=False,
         )
         assert len(response) > 0
         print(f"  response: {response}")
@@ -317,6 +310,7 @@ class TestLiveOverrides:
 # Scenario 9: Error resilience
 # ===========================================================================
 
+
 class TestLiveErrorResilience:
     def test_delete_nonexistent_upload(self, client):
         with pytest.raises(FileNotFoundError):

backend/uv.lock

@@ -1,5 +1,5 @@
 version = 1
-revision = 2
+revision = 3
 requires-python = ">=3.12"
 resolution-markers = [
     "python_full_version >= '3.14' and sys_platform == 'win32'",
@@ -131,6 +131,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/fb/76/641ae371508676492379f16e2fa48f4e2c11741bd63c48be4b12a6b09cba/aiosignal-1.4.0-py3-none-any.whl", hash = "sha256:053243f8b92b990551949e63930a839ff0cf0b0ebbe0597b0f3fb19e1a0fe82e", size = 7490, upload-time = "2025-07-03T22:54:42.156Z" },
 ]
 
+[[package]]
+name = "aiosqlite"
+version = "0.22.1"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/4e/8a/64761f4005f17809769d23e518d915db74e6310474e733e3593cfc854ef1/aiosqlite-0.22.1.tar.gz", hash = "sha256:043e0bd78d32888c0a9ca90fc788b38796843360c855a7262a532813133a0650", size = 14821, upload-time = "2025-12-23T19:25:43.997Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/00/b7/e3bf5133d697a08128598c8d0abc5e16377b51465a33756de24fa7dee953/aiosqlite-0.22.1-py3-none-any.whl", hash = "sha256:21c002eb13823fad740196c5a2e9d8e62f6243bd9e7e4a1f87fb5e44ecb4fceb", size = 17405, upload-time = "2025-12-23T19:25:42.139Z" },
+]
+
 [[package]]
 name = "annotated-doc"
 version = "0.0.4"
@@ -149,6 +158,25 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/78/b6/6307fbef88d9b5ee7421e68d78a9f162e0da4900bc5f5793f6d3d0e34fb8/annotated_types-0.7.0-py3-none-any.whl", hash = "sha256:1f02e8b43a8fbbc3f3e0d4f0f4bfc8131bcb4eebe8849b8e5c773f3a1c582a53", size = 13643, upload-time = "2024-05-20T21:33:24.1Z" },
 ]
 
+[[package]]
+name = "anthropic"
+version = "0.84.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "anyio" },
+    { name = "distro" },
+    { name = "docstring-parser" },
+    { name = "httpx" },
+    { name = "jiter" },
+    { name = "pydantic" },
+    { name = "sniffio" },
+    { name = "typing-extensions" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/04/ea/0869d6df9ef83dcf393aeefc12dd81677d091c6ffc86f783e51cf44062f2/anthropic-0.84.0.tar.gz", hash = "sha256:72f5f90e5aebe62dca316cb013629cfa24996b0f5a4593b8c3d712bc03c43c37", size = 539457, upload-time = "2026-02-25T05:22:38.54Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/64/ca/218fa25002a332c0aa149ba18ffc0543175998b1f65de63f6d106689a345/anthropic-0.84.0-py3-none-any.whl", hash = "sha256:861c4c50f91ca45f942e091d83b60530ad6d4f98733bfe648065364da05d29e7", size = 455156, upload-time = "2026-02-25T05:22:40.468Z" },
+]
+
 [[package]]
 name = "anyio"
 version = "4.12.1"
@@ -342,6 +370,11 @@ dependencies = [
 ]
 sdist = { url = "https://files.pythonhosted.org/packages/84/85/57c314a6b35336efbbdc13e5fc9ae13f6b60a0647cfa7c1221178ac6d8ae/brotlicffi-1.2.0.0.tar.gz", hash = "sha256:34345d8d1f9d534fcac2249e57a4c3c8801a33c9942ff9f8574f67a175e17adb", size = 476682, upload-time = "2025-11-21T18:17:57.334Z" }
 wheels = [
+    { url = "https://files.pythonhosted.org/packages/7c/87/ba6298c3d7f8d66ce80d7a487f2a487ebae74a79c6049c7c2990178ce529/brotlicffi-1.2.0.0-cp314-cp314t-macosx_11_0_arm64.whl", hash = "sha256:b13fb476a96f02e477a506423cb5e7bc21e0e3ac4c060c20ba31c44056e38c68", size = 433038, upload-time = "2026-03-05T17:57:37.96Z" },
+    { url = "https://files.pythonhosted.org/packages/00/49/16c7a77d1cae0519953ef0389a11a9c2e2e62e87d04f8e7afbae40124255/brotlicffi-1.2.0.0-cp314-cp314t-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:17db36fb581f7b951635cd6849553a95c6f2f53c1a707817d06eae5aeff5f6af", size = 1541124, upload-time = "2026-03-05T17:57:39.488Z" },
+    { url = "https://files.pythonhosted.org/packages/e8/17/fab2c36ea820e2288f8c1bf562de1b6cd9f30e28d66f1ce2929a4baff6de/brotlicffi-1.2.0.0-cp314-cp314t-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:40190192790489a7b054312163d0ce82b07d1b6e706251036898ce1684ef12e9", size = 1541983, upload-time = "2026-03-05T17:57:41.061Z" },
+    { url = "https://files.pythonhosted.org/packages/78/c9/849a669b3b3bb8ac96005cdef04df4db658c33443a7fc704a6d4a2f07a56/brotlicffi-1.2.0.0-cp314-cp314t-win32.whl", hash = "sha256:a8079e8ecc32ecef728036a1d9b7105991ce6a5385cf51ee8c02297c90fb08c2", size = 349046, upload-time = "2026-03-05T17:57:42.76Z" },
+    { url = "https://files.pythonhosted.org/packages/a4/25/09c0fd21cfc451fa38ad538f4d18d8be566746531f7f27143f63f8c45a9f/brotlicffi-1.2.0.0-cp314-cp314t-win_amd64.whl", hash = "sha256:ca90c4266704ca0a94de8f101b4ec029624273380574e4cf19301acfa46c61a0", size = 385653, upload-time = "2026-03-05T17:57:44.224Z" },
     { url = "https://files.pythonhosted.org/packages/e4/df/a72b284d8c7bef0ed5756b41c2eb7d0219a1dd6ac6762f1c7bdbc31ef3af/brotlicffi-1.2.0.0-cp38-abi3-macosx_11_0_arm64.whl", hash = "sha256:9458d08a7ccde8e3c0afedbf2c70a8263227a68dea5ab13590593f4c0a4fd5f4", size = 432340, upload-time = "2025-11-21T18:17:42.277Z" },
     { url = "https://files.pythonhosted.org/packages/74/2b/cc55a2d1d6fb4f5d458fba44a3d3f91fb4320aa14145799fd3a996af0686/brotlicffi-1.2.0.0-cp38-abi3-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:84e3d0020cf1bd8b8131f4a07819edee9f283721566fe044a20ec792ca8fd8b7", size = 1534002, upload-time = "2025-11-21T18:17:43.746Z" },
     { url = "https://files.pythonhosted.org/packages/e4/9c/d51486bf366fc7d6735f0e46b5b96ca58dc005b250263525a1eea3cd5d21/brotlicffi-1.2.0.0-cp38-abi3-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:33cfb408d0cff64cd50bef268c0fed397c46fbb53944aa37264148614a62e990", size = 1536547, upload-time = "2025-11-21T18:17:45.729Z" },
@@ -619,12 +652,14 @@ dependencies = [
     { name = "httpx" },
     { name = "kubernetes" },
     { name = "langchain" },
+    { name = "langchain-anthropic" },
     { name = "langchain-deepseek" },
     { name = "langchain-google-genai" },
     { name = "langchain-mcp-adapters" },
     { name = "langchain-openai" },
     { name = "langgraph" },
     { name = "langgraph-api" },
+    { name = "langgraph-checkpoint-sqlite" },
     { name = "langgraph-cli" },
     { name = "langgraph-runtime-inmem" },
     { name = "markdownify" },
@@ -656,12 +691,14 @@ requires-dist = [
     { name = "httpx", specifier = ">=0.28.0" },
     { name = "kubernetes", specifier = ">=30.0.0" },
     { name = "langchain", specifier = ">=1.2.3" },
+    { name = "langchain-anthropic", specifier = ">=1.3.4" },
     { name = "langchain-deepseek", specifier = ">=1.0.1" },
     { name = "langchain-google-genai", specifier = ">=4.2.1" },
     { name = "langchain-mcp-adapters", specifier = ">=0.1.0" },
     { name = "langchain-openai", specifier = ">=1.1.7" },
     { name = "langgraph", specifier = ">=1.0.6" },
     { name = "langgraph-api", specifier = ">=0.7.0,<0.8.0" },
+    { name = "langgraph-checkpoint-sqlite", specifier = ">=3.0.3" },
     { name = "langgraph-cli", specifier = ">=0.4.14" },
     { name = "langgraph-runtime-inmem", specifier = ">=0.22.1" },
     { name = "markdownify", specifier = ">=1.2.2" },
@@ -700,6 +737,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/12/b3/231ffd4ab1fc9d679809f356cebee130ac7daa00d6d6f3206dd4fd137e9e/distro-1.9.0-py3-none-any.whl", hash = "sha256:7bffd925d65168f85027d8da9af6bddab658135b840670a223589bc0c8ef02b2", size = 20277, upload-time = "2023-12-24T09:54:30.421Z" },
 ]
 
+[[package]]
+name = "docstring-parser"
+version = "0.17.0"
+source = { registry = "https://pypi.org/simple" }
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+]
+
 [[package]]
 name = "sse-starlette"
 version = "2.1.3"

config.example.yaml

@@ -344,3 +344,37 @@ memory:
   fact_confidence_threshold: 0.7 # Minimum confidence for storing facts
   injection_enabled: true # Whether to inject memory into system prompt
   max_injection_tokens: 2000 # Maximum tokens for memory injection
+
+
+# ============================================================================
+# Checkpointer Configuration
+# ============================================================================
+# Configure state persistence for the embedded DeerFlowClient.
+# The LangGraph Server manages its own state persistence separately
+# via the server infrastructure (this setting does not affect it).
+#
+# When configured, DeerFlowClient will automatically use this checkpointer,
+# enabling multi-turn conversations to persist across process restarts.
+#
+# Supported types:
+#   memory   - In-process only. State is lost when the process exits. (default)
+#   sqlite   - File-based SQLite persistence. Survives restarts.
+#              Requires: uv add langgraph-checkpoint-sqlite
+#   postgres - PostgreSQL persistence. Suitable for multi-process deployments.
+#              Requires: uv add langgraph-checkpoint-postgres psycopg[binary] psycopg-pool
+#
+# Examples:
+#
+# In-memory (default when omitted — no persistence):
+# checkpointer:
+#   type: memory
+#
+# SQLite (file-based, single-process):
+# checkpointer:
+#   type: sqlite
+#   connection_string: checkpoints.db
+#
+# PostgreSQL (multi-process, production):
+# checkpointer:
+#   type: postgres
+#   connection_string: postgresql://user:password@localhost:5432/deerflow