Add src/graph.py

src/graph.py

@@ -0,0 +1,46 @@
+"""
+LangGraph implementation for the research brief generator.
+
+The graph orchestrates the following nodes (defined in ``brief.py``):
+
+* ``outline`` – generates a 4–5 point outline.
+* ``research_step`` – performs a web search for the current outline point and creates a short note.
+* ``synthesize`` – combines all notes into a coherent brief.
+
+The graph loops over ``research_step`` until all outline points are processed.
+"""
+
+from langgraph import StateGraph, END
+from .brief import BriefState, outline_node, research_step_node, synthesize_node
+
+def build_graph() -> StateGraph:
+    """Build and return the LangGraph graph.
+
+    The graph starts at ``outline``.  After generating the outline it
+    proceeds to ``research_step``.  ``research_step`` is repeated until
+    ``step_index`` reaches the length of the outline, then the graph
+    moves to ``synthesize`` and ends.
+    """
+    graph = StateGraph(BriefState)
+
+    # Add nodes
+    graph.add_node("outline", outline_node)
+    graph.add_node("research_step", research_step_node)
+    graph.add_node("synthesize", synthesize_node)
+
+    # Entry point
+    graph.set_entry_point("outline")
+
+    # After outline, always go to research_step
+    graph.add_edge("outline", "research_step")
+
+    # Conditional loop: if more steps remain, stay in research_step
+    def research_cond(state: BriefState):
+        return "research_step" if state["step_index"] < len(state["outline"]) else "synthesize"
+
+    graph.add_conditional_edges("research_step", research_cond)
+
+    # End after synthesis
+    graph.add_edge("synthesize", END)
+
+    return graph