LangGraph server lifecycle management for the CLI.
Handles starting/stopping a langgraph dev server process and generating the
required langgraph.json configuration file.
Build the server base URL.
Generate a langgraph.json config file for langgraph dev.
Poll a LangGraph server health endpoint until it responds.
Manages a langgraph dev server subprocess.
Focuses on subprocess lifecycle (start, stop, restart) and health checking.
Env-var management for restarts (e.g. configuration changes requiring a full
restart) is handled by _scoped_env_overrides, keeping this class focused
on process management.
