style(langgraph): clean up code

libs/langgraph/langgraph/_internal/_constants.py

@@ -24,7 +24,6 @@ PREVIOUS = sys.intern("__previous__")
 
 # --- Reserved cache namespaces ---
 CACHE_NS_WRITES = sys.intern("__pregel_ns_writes")
-
 # cache namespace for node writes
 
 # --- Reserved config.configurable keys ---
@@ -78,8 +77,6 @@ CONF = cast(Literal["configurable"], sys.intern("configurable"))
 # key for the configurable dict in RunnableConfig
 NULL_TASK_ID = sys.intern("00000000-0000-0000-0000-000000000000")
 # the task_id to use for writes that are not associated with a task
-UNTRACKED_VALUE_PLACEHOLDER = sys.intern("__pregel_untracked_value_placeholder")
-# placeholder for untracked values replaced at runtime
 
 # redefined to avoid circular import with langgraph.constants
 _TAG_HIDDEN = sys.intern("langsmith:hidden")

libs/langgraph/langgraph/pregel/_algo.py

@@ -58,7 +58,6 @@ from langgraph._internal._constants import (
     RESUME,
     RETURN,
     TASKS,
-    UNTRACKED_VALUE_PLACEHOLDER,
 )
 from langgraph._internal._scratchpad import PregelScratchpad
 from langgraph._internal._typing import EMPTY_SEQ, MISSING
@@ -1114,9 +1113,9 @@ class LazyAtomicCounter:
 def sanitize_untracked_values_in_send(
     packet: Send, channels: Mapping[str, BaseChannel]
 ) -> Send:
-    """Replace any UntrackedValue contents in Send.arg with UNTRACKED_VALUE_PLACEHOLDER for checkpointing.
+    """Pop any UntrackedValue contents in Send.arg for safe checkpointing.
 
-    Send is not typed and arg may be a nested dict."""
+    Send is not typed and arg may be a nested dict. We only look at the top level."""
 
     if not isinstance(packet.arg, dict):
         # Command
@@ -1124,8 +1123,12 @@ def sanitize_untracked_values_in_send(
 
     sanitized_arg = dict(packet.arg)
 
+    # top level keys should be the channel names
+    to_pop = set()
     for k, v in sanitized_arg.items():
         if isinstance(channels.get(k), UntrackedValue):
-            sanitized_arg[k] = UNTRACKED_VALUE_PLACEHOLDER
+            to_pop.add(k)
+    for k in to_pop:
+        sanitized_arg.pop(k)
 
     return Send(node=packet.node, arg=sanitized_arg)

libs/langgraph/langgraph/pregel/_loop.py

@@ -325,20 +325,20 @@ class PregelLoop:
             ]
             writes_to_save = writes
 
-        # Check if any writes are to an UntrackedValue channel
+        # check if any writes are to an UntrackedValue channel
         if any(
             isinstance(channel, UntrackedValue) for channel in self.channels.values()
         ):
-            # We do not persist untracked values in checkpoints
+            # we do not persist untracked values in checkpoints
             writes_to_save = [
-                # Sanitize UntrackedValues that are nested within Send packets
+                # sanitize UntrackedValues that are nested within Send packets
                 (
                     (c, sanitize_untracked_values_in_send(v, self.channels))
                     if c == TASKS and isinstance(v, Send)
                     else (c, v)
                 )
                 for c, v in writes_to_save
-                # Do not persist UntrackedValue channel writes
+                # dont persist UntrackedValue channel writes
                 if not isinstance(self.specs.get(c), UntrackedValue)
             ]
 
@@ -757,7 +757,7 @@ class PregelLoop:
             id=self.checkpoint["id"] if exiting else None,
             updated_channels=self.updated_channels,
         )
-        # sanitize TASK channel in the checkpoint before saving
+        # sanitize TASK channel in the checkpoint before saving (durability=="exit")
         if TASKS in self.checkpoint["channel_values"] and any(
             isinstance(channel, UntrackedValue) for channel in self.channels.values()
         ):

libs/langgraph/langgraph/pregel/_write.py

@@ -176,8 +176,6 @@ def _assemble_writes(
     tuples: list[tuple[str, Any]] = []
     for w in writes:
         if isinstance(w, Send):
-            # Send packets go to TASKS channel; sanitation for storage
-            # is handled centrally where channel specs are available.
             tuples.append((TASKS, w))
         elif isinstance(w, ChannelWriteTupleEntry):
             if ww := w.mapper(w.value):