WIP: monorepo support in CLI (#6028)

This PR introduces the `--build-command` and `--install-command`
arguments to `langgraph build`.

`--install-command` is a custom install command. If passed, it will be
run from wherever the `langgraph build` call was made, i.e. NOT where
the langgraph.json file lives (except if these are the same place). This
will override the detected install command that we previously used.

`--build-command` is a custom build command. This will run from wherever
the langgraph.json file lives, and will be done after the install has
been run.

You don't need to provide both. Just providing one will make the install
(detected or supplied) run in the directory from where `langgraph build
was called` and then have the build command (if one exists) run in the
directory where langgraph.json exists.

I think we should probably allow configuring the directories from which
these commands get run, but I don't think this needs to be part of the
MVP.

---------

Co-authored-by: William FH <13333726+hinthornw@users.noreply.github.com>

libs/cli/js-monorepo-example/apps/agent/src/graph.ts

@@ -0,0 +1,47 @@
+/**
+ * Simple LangGraph.js example for monorepo testing
+ */
+import { StateGraph } from "@langchain/langgraph";
+import { RunnableConfig } from "@langchain/core/runnables";
+import { StateAnnotation } from "./state.js";
+import { getGreeting } from "@js-monorepo-example/shared";
+
+/**
+ * Simple node that uses the shared library
+ */
+const callModel = async (
+  state: typeof StateAnnotation.State,
+  _config: RunnableConfig,
+): Promise<typeof StateAnnotation.Update> => {
+  // Use functions from the shared library
+  const greeting = getGreeting();
+
+  return {
+    messages: [
+      {
+        role: "assistant",
+        content: `${greeting}`,
+      },
+    ],
+  };
+};
+
+/**
+ * Simple routing function
+ */
+export const route = (
+  state: typeof StateAnnotation.State,
+): "__end__" | "callModel" => {
+  if (state.messages.length > 0) {
+    return "__end__";
+  }
+  return "callModel";
+};
+
+// Create the graph
+const builder = new StateGraph(StateAnnotation)
+  .addNode("callModel", callModel)
+  .addEdge("__start__", "callModel")
+  .addConditionalEdges("callModel", route);
+
+export const graph = builder.compile();

libs/cli/js-monorepo-example/apps/agent/src/state.ts

@@ -0,0 +1,15 @@
+import { BaseMessage, BaseMessageLike } from "@langchain/core/messages";
+import { Annotation, messagesStateReducer } from "@langchain/langgraph";
+
+/**
+ * Simple state annotation for the agent
+ */
+export const StateAnnotation = Annotation.Root({
+  /**
+   * Messages track the primary execution state of the agent.
+   */
+  messages: Annotation<BaseMessage[], BaseMessageLike[]>({
+    reducer: messagesStateReducer,
+    default: () => [],
+  }),
+});