From a885b1ca532bb66c92acc063ae7ac797f4c66576 Mon Sep 17 00:00:00 2001
From: Nuno Campos <nuno@langchain.dev>
Date: Mon, 13 May 2024 17:28:06 -0700
Subject: [PATCH] Small fixes while migrating JS

---
 langgraph/channels/base.py   | 4 +++-
 langgraph/graph/graph.py     | 7 ++++---
 langgraph/graph/state.py     | 2 +-
 langgraph/pregel/__init__.py | 6 ------
 4 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/langgraph/channels/base.py b/langgraph/channels/base.py
index 7dd63e9bb..ae6869b41 100644
--- a/langgraph/channels/base.py
+++ b/langgraph/channels/base.py
@@ -114,7 +114,9 @@ def create_checkpoint(
 ) -> Checkpoint:
     """Create a checkpoint for the given channels."""
     ts = datetime.now(timezone.utc).isoformat()
-    assert ts > checkpoint["ts"], "Timestamps must be monotonically increasing"
+    assert (
+        ts > checkpoint["ts"]
+    ), f"Timestamps must be monotonically increasing, got {ts} <= {checkpoint['ts']}"
     values: dict[str, Any] = {}
     for k, v in channels.items():
         try:
diff --git a/langgraph/graph/graph.py b/langgraph/graph/graph.py
index 818bc4de4..44f3a29f3 100644
--- a/langgraph/graph/graph.py
+++ b/langgraph/graph/graph.py
@@ -242,12 +242,13 @@ class Graph:
         # assemble sources
         all_sources = {src for src, _ in self._all_edges}
         for start, branches in self.branches.items():
+            all_sources.add(start)
             for cond, branch in branches.items():
-                all_sources.add(start)
                 if branch.then is not None:
                     if branch.ends is not None:
                         for end in branch.ends.values():
-                            all_sources.add(end)
+                            if end != END:
+                                all_sources.add(end)
                     else:
                         for node in self.nodes:
                             if node != start and node != branch.then:
@@ -257,7 +258,7 @@ class Graph:
             if node not in all_sources:
                 raise ValueError(f"Node '{node}' is a dead-end")
         for source in all_sources:
-            if node not in self.nodes and node != START:
+            if node not in self.nodes and source != START:
                 raise ValueError(f"Found edge starting at unknown node '{source}'")
 
         # assemble targets
diff --git a/langgraph/graph/state.py b/langgraph/graph/state.py
index 9d121159d..1b2a4622f 100644
--- a/langgraph/graph/state.py
+++ b/langgraph/graph/state.py
@@ -269,7 +269,7 @@ class CompiledStateGraph(CompiledGraph):
             elif end != END:
                 # subscribe to start channel
                 self.nodes[end].triggers.append(starts)
-        else:
+        elif end != END:
             channel_name = f"join:{'+'.join(starts)}:{end}"
             # register channel
             self.channels[channel_name] = NamedBarrierValue(str, set(starts))
diff --git a/langgraph/pregel/__init__.py b/langgraph/pregel/__init__.py
index 597f617d5..9549c2bad 100644
--- a/langgraph/pregel/__init__.py
+++ b/langgraph/pregel/__init__.py
@@ -108,12 +108,6 @@ WriteValue = Union[
 ]
 
 
-def _coerce_write_value(value: WriteValue) -> Runnable[Input, Output]:
-    if not isinstance(value, Runnable) and not callable(value):
-        return coerce_to_runnable(lambda _: value)
-    return coerce_to_runnable(value)
-
-
 class Channel:
     @overload
     @classmethod