Handle missing pgvector tables on first run

_get_collection_id now catches the UndefinedTable error that occurs
before the first index operation creates the langchain tables.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blueprints/rag/logic.py

@@ -59,6 +59,7 @@ text_splitter = RecursiveCharacterTextSplitter(
 def _get_collection_id():
     """Get the UUID of our collection from the langchain_pg_collection table."""
     engine = _get_engine()
+    try:
         with engine.connect() as conn:
             result = conn.execute(
                 text("SELECT uuid FROM langchain_pg_collection WHERE name = :name"),
@@ -66,6 +67,9 @@ def _get_collection_id():
             )
             row = result.fetchone()
             return row[0] if row else None
+    except Exception:
+        # Table doesn't exist yet (first run before any indexing)
+        return None
 
 
 def date_to_epoch(date_str: str) -> float: