Use a different strategy, add test

libs/langgraph/langgraph/constants.py

@@ -10,6 +10,14 @@
 EMPTY_MAP: Mapping[str, Any] = MappingProxyType({})
 EMPTY_SEQ: tuple[str, ...] = tuple()
 
+# --- Public constants ---
+TAG_HIDDEN = "langsmith:hidden"
+# tag to hide a node/edge from certain tracing/streaming environments
+START = "__start__"
+# the first (maybe virtual) node in graph-style Pregel
+END = "__end__"
+# the last (maybe virtual) node in graph-style Pregel
+
 # --- Reserved write keys ---
 INPUT = "__input__"
 # for values passed as input to the graph
@@ -23,10 +31,6 @@
 # marker to signal node was scheduled (in distributed mode)
 TASKS = "__pregel_tasks"
 # for Send objects returned by nodes/edges, corresponds to PUSH below
-START = "__start__"
-# marker for the first (maybe virtual) node in graph-style Pregel
-END = "__end__"
-# marker for the last (maybe virtual) node in graph-style Pregel
 
 # --- Reserved config.configurable keys ---
 CONFIG_KEY_SEND = "__pregel_send"
@@ -43,8 +47,6 @@
 # holds a `BaseStore` made available to managed values
 CONFIG_KEY_RESUMING = "__pregel_resuming"
 # holds a boolean indicating if subgraphs should resume from a previous checkpoint
-CONFIG_KEY_GRAPH_COUNT = "__pregel_graph_count"
-# holds the number of subgraphs executed in a given task, used to raise errors
 CONFIG_KEY_TASK_ID = "__pregel_task_id"
 # holds the task ID for the current task
 CONFIG_KEY_DEDUPE_TASKS = "__pregel_dedupe_tasks"
@@ -68,14 +70,13 @@
 # denotes pull-style tasks, ie. those triggered by edges
 RUNTIME_PLACEHOLDER = "__pregel_runtime_placeholder__"
 # placeholder for managed values replaced at runtime
-TAG_HIDDEN = "langsmith:hidden"
-# tag to hide a node/edge from certain tracing/streaming environments
 NS_SEP = "|"
 # for checkpoint_ns, separates each level (ie. graph|subgraph|subsubgraph)
 NS_END = ":"
 # for checkpoint_ns, for each level, separates the namespace from the task_id
 
 RESERVED = {
+    TAG_HIDDEN,
     # reserved write keys
     INPUT,
     INTERRUPT,
@@ -103,7 +104,6 @@
     PUSH,
     PULL,
     RUNTIME_PLACEHOLDER,
-    TAG_HIDDEN,
     NS_SEP,
     NS_END,
 }

libs/langgraph/langgraph/errors.py

@@ -69,3 +69,13 @@ class CheckpointNotLatest(Exception):
     """Raised when the checkpoint is not the latest version (for distributed mode)."""
 
     pass
+
+
+class MultipleSubgraphsError(Exception):
+    """Raised when multiple subgraphs are called inside the same node."""
+
+    pass
+
+
+_SEEN_CHECKPOINT_NS: set[str] = set()
+"""Used for subgraph detection."""

libs/langgraph/langgraph/graph/graph.py

@@ -26,7 +26,6 @@
 from typing_extensions import Self
 
 from langgraph.channels.ephemeral_value import EphemeralValue
-from langgraph.checkpoint.base import BaseCheckpointSaver
 from langgraph.constants import (
     END,
     NS_END,
@@ -39,7 +38,7 @@
 from langgraph.pregel import Channel, Pregel
 from langgraph.pregel.read import PregelNode
 from langgraph.pregel.write import ChannelWrite, ChannelWriteEntry
-from langgraph.types import All
+from langgraph.types import All, Checkpointer
 from langgraph.utils.runnable import RunnableCallable, coerce_to_runnable
 
 logger = logging.getLogger(__name__)
@@ -406,7 +405,7 @@ def validate(self, interrupt: Optional[Sequence[str]] = None) -> Self:
 
     def compile(
         self,
-        checkpointer: Optional[BaseCheckpointSaver] = None,
+        checkpointer: Checkpointer = None,
         interrupt_before: Optional[Union[All, list[str]]] = None,
         interrupt_after: Optional[Union[All, list[str]]] = None,
         debug: bool = False,

libs/langgraph/langgraph/graph/state.py

@@ -32,7 +32,6 @@
 from langgraph.channels.ephemeral_value import EphemeralValue
 from langgraph.channels.last_value import LastValue
 from langgraph.channels.named_barrier_value import NamedBarrierValue
-from langgraph.checkpoint.base import BaseCheckpointSaver
 from langgraph.constants import NS_END, NS_SEP, TAG_HIDDEN
 from langgraph.errors import InvalidUpdateError
 from langgraph.graph.graph import END, START, Branch, CompiledGraph, Graph, Send
@@ -47,7 +46,7 @@
 from langgraph.pregel.read import ChannelRead, PregelNode
 from langgraph.pregel.write import SKIP_WRITE, ChannelWrite, ChannelWriteEntry
 from langgraph.store.base import BaseStore
-from langgraph.types import All, RetryPolicy
+from langgraph.types import All, Checkpointer, RetryPolicy
 from langgraph.utils.fields import get_field_default
 from langgraph.utils.pydantic import create_model
 from langgraph.utils.runnable import coerce_to_runnable
@@ -400,7 +399,7 @@ def add_edge(self, start_key: Union[str, list[str]], end_key: str) -> Self:
 
     def compile(
         self,
-        checkpointer: Optional[BaseCheckpointSaver] = None,
+        checkpointer: Checkpointer = None,
         *,
         store: Optional[BaseStore] = None,
         interrupt_before: Optional[Union[All, list[str]]] = None,
@@ -413,7 +412,7 @@ def compile(
         streamed, batched, and run asynchronously.
 
         Args:
-            checkpointer (Optional[BaseCheckpointSaver]): An optional checkpoint saver object.
+            checkpointer (Checkpointer): An optional checkpoint saver object.
                 This serves as a fully versioned "memory" for the graph, allowing
                 the graph to be paused and resumed, and replayed from any point.
             interrupt_before (Optional[Sequence[str]]): An optional list of node names to interrupt before.

libs/langgraph/langgraph/prebuilt/chat_agent_executor.py

@@ -16,13 +16,13 @@
 from langchain_core.tools import BaseTool
 
 from langgraph._api.deprecation import deprecated_parameter
-from langgraph.checkpoint.base import BaseCheckpointSaver
 from langgraph.graph import StateGraph
 from langgraph.graph.graph import CompiledGraph
 from langgraph.graph.message import add_messages
 from langgraph.managed import IsLastStep
 from langgraph.prebuilt.tool_executor import ToolExecutor
 from langgraph.prebuilt.tool_node import ToolNode
+from langgraph.types import Checkpointer
 
 
 # We create the AgentState that we will pass around
@@ -132,7 +132,7 @@ def create_react_agent(
     state_schema: Optional[StateSchemaType] = None,
     messages_modifier: Optional[MessagesModifier] = None,
     state_modifier: Optional[StateModifier] = None,
-    checkpointer: Optional[BaseCheckpointSaver] = None,
+    checkpointer: Checkpointer = None,
     interrupt_before: Optional[list[str]] = None,
     interrupt_after: Optional[list[str]] = None,
     debug: bool = False,

libs/langgraph/langgraph/pregel/__init__.py

@@ -87,7 +87,7 @@
 from langgraph.pregel.validate import validate_graph, validate_keys
 from langgraph.pregel.write import ChannelWrite, ChannelWriteEntry
 from langgraph.store.base import BaseStore
-from langgraph.types import All, StateSnapshot, StreamMode
+from langgraph.types import All, Checkpointer, StateSnapshot, StreamMode
 from langgraph.utils.config import (
     ensure_config,
     merge_configs,
@@ -197,7 +197,7 @@ class Pregel(Runnable[Union[dict[str, Any], Any], Union[dict[str, Any], Any]]):
     debug: bool
     """Whether to print debug information during execution. Defaults to False."""
 
-    checkpointer: Optional[BaseCheckpointSaver] = None
+    checkpointer: Checkpointer = None
     """Checkpointer used to save and load graph state. Defaults to None."""
 
     store: Optional[BaseStore] = None
@@ -281,7 +281,7 @@ def config_specs(self) -> list[ConfigurableFieldSpec]:
                 [spec for node in self.nodes.values() for spec in node.config_specs]
                 + (
                     self.checkpointer.config_specs
-                    if self.checkpointer is not None
+                    if isinstance(self.checkpointer, BaseCheckpointSaver)
                     else []
                 )
                 + (
@@ -1059,6 +1059,8 @@ def _defaults(
         Union[All, Sequence[str]],
         Optional[BaseCheckpointSaver],
     ]:
+        if config["recursion_limit"] < 1:
+            raise ValueError("recursion_limit must be at least 1")
         debug = debug if debug is not None else self.debug
         if output_keys is None:
             output_keys = self.stream_channels_asis
@@ -1072,12 +1074,16 @@ def _defaults(
         if CONFIG_KEY_TASK_ID in config.get("configurable", {}):
             # if being called as a node in another graph, always use values mode
             stream_mode = ["values"]
-        if CONFIG_KEY_CHECKPOINTER in config.get("configurable", {}):
-            checkpointer: Optional[BaseCheckpointSaver] = config["configurable"][
-                CONFIG_KEY_CHECKPOINTER
-            ]
+        if self.checkpointer is False:
+            checkpointer: Optional[BaseCheckpointSaver] = None
+        elif CONFIG_KEY_CHECKPOINTER in config.get("configurable", {}):
+            checkpointer = config["configurable"][CONFIG_KEY_CHECKPOINTER]
         else:
             checkpointer = self.checkpointer
+        if checkpointer and not config.get("configurable"):
+            raise ValueError(
+                f"Checkpointer requires one or more of the following 'configurable' keys: {[s.id for s in checkpointer.config_specs]}"
+            )
         return (
             debug,
             set(stream_mode),
@@ -1193,12 +1199,6 @@ def output() -> Iterator:
             run_id=config.get("run_id"),
         )
         try:
-            if config["recursion_limit"] < 1:
-                raise ValueError("recursion_limit must be at least 1")
-            if self.checkpointer and not config.get("configurable"):
-                raise ValueError(
-                    f"Checkpointer requires one or more of the following 'configurable' keys: {[s.id for s in self.checkpointer.config_specs]}"
-                )
             # assign defaults
             (
                 debug,
@@ -1414,12 +1414,6 @@ def output() -> Iterator:
             None,
         )
         try:
-            if config["recursion_limit"] < 1:
-                raise ValueError("recursion_limit must be at least 1")
-            if self.checkpointer and not config.get("configurable"):
-                raise ValueError(
-                    f"Checkpointer requires one or more of the following 'configurable' keys: {[s.id for s in self.checkpointer.config_specs]}"
-                )
             # assign defaults
             (
                 debug,

libs/langgraph/langgraph/pregel/algo.py

@@ -30,7 +30,6 @@
 from langgraph.constants import (
     CONFIG_KEY_CHECKPOINT_MAP,
     CONFIG_KEY_CHECKPOINTER,
-    CONFIG_KEY_GRAPH_COUNT,
     CONFIG_KEY_READ,
     CONFIG_KEY_SEND,
     CONFIG_KEY_TASK_ID,
@@ -430,7 +429,6 @@ def prepare_single_task(
                             manager.get_child(f"graph:step:{step}") if manager else None
                         ),
                         configurable={
-                            CONFIG_KEY_GRAPH_COUNT: 0,
                             CONFIG_KEY_TASK_ID: task_id,
                             # deque.extend is thread-safe
                             CONFIG_KEY_SEND: partial(
@@ -541,7 +539,6 @@ def prepare_single_task(
                                 else None
                             ),
                             configurable={
-                                CONFIG_KEY_GRAPH_COUNT: 0,
                                 CONFIG_KEY_TASK_ID: task_id,
                                 # deque.extend is thread-safe
                                 CONFIG_KEY_SEND: partial(

libs/langgraph/langgraph/pregel/loop.py

@@ -41,7 +41,6 @@
     CONFIG_KEY_DEDUPE_TASKS,
     CONFIG_KEY_DELEGATE,
     CONFIG_KEY_ENSURE_LATEST,
-    CONFIG_KEY_GRAPH_COUNT,
     CONFIG_KEY_RESUMING,
     CONFIG_KEY_STREAM,
     CONFIG_KEY_TASK_ID,
@@ -55,10 +54,12 @@
     TASKS,
 )
 from langgraph.errors import (
+    _SEEN_CHECKPOINT_NS,
     CheckpointNotLatest,
     EmptyInputError,
     GraphDelegate,
     GraphInterrupt,
+    MultipleSubgraphsError,
 )
 from langgraph.managed.base import (
     ManagedValueMapping,
@@ -221,12 +222,11 @@ def __init__(
             self.config = patch_configurable(
                 self.config, {"checkpoint_ns": "", "checkpoint_id": None}
             )
-        if self.is_nested:
-            if config["configurable"].get(CONFIG_KEY_GRAPH_COUNT, 0) > 0:
-                raise ValueError("Detected multiple subgraphs called in a single node.")
+        if self.is_nested and self.checkpointer is not None:
+            if self.config["configurable"]["checkpoint_ns"] in _SEEN_CHECKPOINT_NS:
+                raise MultipleSubgraphsError
             else:
-                # mutate config so that sibling subgraphs can be detected
-                self.config["configurable"][CONFIG_KEY_GRAPH_COUNT] = 1
+                _SEEN_CHECKPOINT_NS.add(self.config["configurable"]["checkpoint_ns"])
         if (
             CONFIG_KEY_CHECKPOINT_MAP in self.config["configurable"]
             and self.config["configurable"].get("checkpoint_ns")

libs/langgraph/langgraph/pregel/retry.py

@@ -4,8 +4,8 @@
 import time
 from typing import Optional, Sequence
 
-from langgraph.constants import CONFIG_KEY_GRAPH_COUNT, CONFIG_KEY_RESUMING
-from langgraph.errors import GraphInterrupt
+from langgraph.constants import CONFIG_KEY_RESUMING
+from langgraph.errors import _SEEN_CHECKPOINT_NS, GraphInterrupt
 from langgraph.types import PregelExecutableTask, RetryPolicy
 from langgraph.utils.config import patch_configurable
 
@@ -70,9 +70,14 @@ def run_with_retry(
                 exc_info=exc,
             )
             # signal subgraphs to resume (if available)
-            config = patch_configurable(
-                config, {CONFIG_KEY_RESUMING: True, CONFIG_KEY_GRAPH_COUNT: 0}
-            )
+            config = patch_configurable(config, {CONFIG_KEY_RESUMING: True})
+            # clear checkpoint_ns seen (for subgraph detection)
+            if checkpoint_ns := config["configurable"].get("checkpoint_ns"):
+                _SEEN_CHECKPOINT_NS.discard(checkpoint_ns)
+        finally:
+            # clear checkpoint_ns seen (for subgraph detection)
+            if checkpoint_ns := config["configurable"].get("checkpoint_ns"):
+                _SEEN_CHECKPOINT_NS.discard(checkpoint_ns)
 
 
 async def arun_with_retry(
@@ -138,6 +143,11 @@ async def arun_with_retry(
                 exc_info=exc,
             )
             # signal subgraphs to resume (if available)
-            config = patch_configurable(
-                config, {CONFIG_KEY_RESUMING: True, CONFIG_KEY_GRAPH_COUNT: 0}
-            )
+            config = patch_configurable(config, {CONFIG_KEY_RESUMING: True})
+            # clear checkpoint_ns seen (for subgraph detection)
+            if checkpoint_ns := config["configurable"].get("checkpoint_ns"):
+                _SEEN_CHECKPOINT_NS.discard(checkpoint_ns)
+        finally:
+            # clear checkpoint_ns seen (for subgraph detection)
+            if checkpoint_ns := config["configurable"].get("checkpoint_ns"):
+                _SEEN_CHECKPOINT_NS.discard(checkpoint_ns)

libs/langgraph/langgraph/types.py

@@ -1,12 +1,26 @@
 from collections import deque
 from dataclasses import dataclass
-from typing import Any, Callable, Literal, NamedTuple, Optional, Sequence, Type, Union
+from typing import (
+    Any,
+    Callable,
+    Literal,
+    NamedTuple,
+    Optional,
+    Sequence,
+    Type,
+    Union,
+)
 
 from langchain_core.runnables import Runnable, RunnableConfig
 
-from langgraph.checkpoint.base import CheckpointMetadata
+from langgraph.checkpoint.base import BaseCheckpointSaver, CheckpointMetadata
 
 All = Literal["*"]
+"""Special value to indicate that graph should interrupt on all nodes."""
+
+Checkpointer = Union[None, Literal[False], BaseCheckpointSaver]
+"""Type of the checkpointer to use for a subgraph. False disables checkpointing,
+even if the parent graph has a checkpointer. None inherits checkpointer."""
 
 StreamMode = Literal["values", "updates", "debug", "messages", "custom"]
 """How the stream method should emit outputs.