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/python-monorepo-example/apps/agent/langgraph.json

@@ -0,0 +1,7 @@
+{
+  "dependencies": [".", "../../libs/shared", "../../libs/common"],
+  "graphs": {
+    "agent": "./src/agent/graph.py:graph"
+  },
+  "env": ".env"
+}

libs/cli/python-monorepo-example/apps/agent/pyproject.toml

@@ -0,0 +1,19 @@
+[project]
+name = "agent"
+version = "0.0.1"
+description = "Agent for the Python monorepo"
+authors = [
+    { name = "Developer", email = "dev@example.com" },
+]
+license = { text = "MIT" }
+requires-python = ">=3.11,<4.0"
+
+[build-system]
+requires = ["setuptools>=73.0.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+packages = ["agent"]
+
+[tool.setuptools.package-dir]
+"agent" = "src/agent"

libs/cli/python-monorepo-example/apps/agent/src/agent/__init__.py

@@ -0,0 +1 @@
+"""Agent package."""

libs/cli/python-monorepo-example/apps/agent/src/agent/graph.py

@@ -0,0 +1,40 @@
+"""Simple LangGraph agent for monorepo testing."""
+
+from common import get_common_prefix
+from langchain_core.messages import AIMessage
+from langgraph.graph import END, START, StateGraph
+from shared import get_dummy_message
+
+from agent.state import State
+
+
+def call_model(state: State) -> dict:
+    """Simple node that uses the shared libraries."""
+    # Use functions from both shared packages
+    dummy_message = get_dummy_message()
+    prefix = get_common_prefix()
+
+    message = AIMessage(content=f"{prefix} Agent says: {dummy_message}")
+
+    return {"messages": [message]}
+
+
+def should_continue(state: State):
+    """Conditional edge - end after first message."""
+    messages = state["messages"]
+    if len(messages) > 0:
+        return END
+    return "call_model"
+
+
+# Build the graph
+workflow = StateGraph(State)
+
+# Add the node
+workflow.add_node("call_model", call_model)
+
+# Add edges
+workflow.add_edge(START, "call_model")
+workflow.add_conditional_edges("call_model", should_continue)
+
+graph = workflow.compile()

libs/cli/python-monorepo-example/apps/agent/src/agent/state.py

@@ -0,0 +1,13 @@
+"""State definition for the agent."""
+
+from collections.abc import Sequence
+from typing import Annotated, TypedDict
+
+from langchain_core.messages import BaseMessage
+from langgraph.graph.message import add_messages
+
+
+class State(TypedDict):
+    """The state of the agent."""
+
+    messages: Annotated[Sequence[BaseMessage], add_messages]