docs: __start__/__end__ consistency (#1874)

* changes

* skip mermaid

* retries fix

* viz error

* changes

docs/docs/tutorials/plan-and-execute/plan-and-execute.ipynb

@@ -391,7 +391,7 @@
    "outputs": [],
    "source": [
     "from typing import Literal\n",
-    "\n",
+    "from langgraph.graph import END\n",
     "\n",
     "async def execute_step(state: PlanExecute):\n",
     "    plan = state[\"plan\"]\n",
@@ -420,9 +420,9 @@
     "        return {\"plan\": output.action.steps}\n",
     "\n",
     "\n",
-    "def should_end(state: PlanExecute) -> Literal[\"agent\", \"__end__\"]:\n",
+    "def should_end(state: PlanExecute):\n",
     "    if \"response\" in state and state[\"response\"]:\n",
-    "        return \"__end__\"\n",
+    "        return END\n",
     "    else:\n",
     "        return \"agent\""
    ]
@@ -459,6 +459,7 @@
     "    \"replan\",\n",
     "    # Next, we pass in the function that will determine which node is called next.\n",
     "    should_end,\n",
+    "    [\"agent\",END]\n",
     ")\n",
     "\n",
     "# Finally, we compile it!\n",