feat: lite deep researcher implementation

src/graph/builder.py

@@ -0,0 +1,30 @@
+from langgraph.graph import StateGraph, START, END
+from langgraph.checkpoint.memory import MemorySaver
+from .types import State
+from .nodes import (
+    coordinator_node,
+    planner_node,
+    reporter_node,
+    research_team_node,
+    researcher_node,
+    coder_node,
+)
+
+
+def build_graph():
+    """Build and return the agent workflow graph."""
+    # use persistent memory to save conversation history
+    # TODO: be compatible with SQLite / PostgreSQL
+    memory = MemorySaver()
+
+    # build state graph
+    builder = StateGraph(State)
+    builder.add_edge(START, "coordinator")
+    builder.add_node("coordinator", coordinator_node)
+    builder.add_node("planner", planner_node)
+    builder.add_node("reporter", reporter_node)
+    builder.add_node("research_team", research_team_node)
+    builder.add_node("researcher", researcher_node)
+    builder.add_node("coder", coder_node)
+    builder.add_edge("reporter", END)
+    return builder.compile(checkpointer=memory)