add lookback for sources in re-ranker

chain.py

@@ -110,10 +110,18 @@ class RagChain:
             for doc in retrieved_docs
         ]
 
+        # Build a lookup map from page_content -> source using the original
+        # retrieved docs, because VertexAIRank strips metadata (including source)
+        # from the documents it returns.
+        source_lookup: dict[str, str] = {
+            doc.page_content: doc.metadata.get("source", "") for doc in retrieved_docs
+        }
+
         self._reranked_sources = [
             {
                 "relevance_score": doc.metadata.get("relevance_score", ""),
                 "page_content": f"{doc.page_content[:50]}...",
+                "source": source_lookup.get(doc.page_content, ""),
             }
             for doc in reranked_docs
         ]
@@ -129,8 +137,9 @@ class RagChain:
             print("========== RERANKED DOCUMENTS ==========")
             for idx, doc in enumerate(reranked_docs, start=1):
                 snippet = doc.page_content[:200].replace("\n", " ")
+                source = source_lookup.get(doc.page_content, "")
                 print(
-                    f"[{idx}] metadata={doc.metadata['relevance_score']} | snippet=...{snippet}..."
+                    f"[{idx}] source={source} | relevance_score={doc.metadata.get('relevance_score', '')} | snippet=...{snippet}..."
                 )
 
         return "\n\n".join(doc.page_content for doc in reranked_docs)