core[minor]: update draw_mermaid node label processing (#23285)

This fixes processing issue for nodes with numbers in their labels (e.g.
`"node_1"`, which would previously be relabeled as `"node__"`, and now
are correctly processed as `"node_1"`)

libs/core/langchain_core/runnables/graph_mermaid.py

@@ -114,7 +114,7 @@ def draw_mermaid(
 
 def _escape_node_label(node_label: str) -> str:
     """Escapes the node label for Mermaid syntax."""
-    return re.sub(r"[^a-zA-Z-_]", "_", node_label)
+    return re.sub(r"[^a-zA-Z-_0-9]", "_", node_label)
 
 
 def _adjust_mermaid_edge(

libs/core/tests/unit_tests/runnables/test_graph.py

@@ -8,6 +8,7 @@ from langchain_core.output_parsers.string import StrOutputParser
 from langchain_core.output_parsers.xml import XMLOutputParser
 from langchain_core.prompts.prompt import PromptTemplate
 from langchain_core.runnables.base import Runnable, RunnableConfig
+from langchain_core.runnables.graph_mermaid import _escape_node_label
 from tests.unit_tests.stubs import AnyStr
 
 
@@ -734,3 +735,11 @@ def test_runnable_get_graph_with_invalid_output_type() -> None:
     assert runnable.invoke(1) == 1
     # check whether runnable.get_graph works
     runnable.get_graph()
+
+
+def test_graph_mermaid_escape_node_label() -> None:
+    """Test that node labels are correctly preprocessed for draw_mermaid"""
+    assert _escape_node_label("foo") == "foo"
+    assert _escape_node_label("foo-bar") == "foo-bar"
+    assert _escape_node_label("foo_1") == "foo_1"
+    assert _escape_node_label("#foo*&!") == "_foo___"