Make a Langfuse trace worth opening: question, answer, session, no probe noise

apps/ai-service/adapters/postgres.py

@@ -191,6 +191,28 @@ class PostgresTraceRepository:
             raise FeedbackTraceNotFound(trace_id)
         return str(row[0])
 
+    def otel_trace_id_for(self, trace_id: str) -> str | None:
+        """The OpenTelemetry id of a persisted answer, for attaching a score.
+
+        Separate from `save_feedback` rather than folded into its RETURNING
+        clause: that method's `-> str` shape is part of the `TraceWriter`
+        protocol the router depends on, and widening it to carry an unrelated
+        id would make every implementation and test carry it too. Feedback is
+        rare enough that a second short query costs nothing.
+
+        None when the row has no OTel id -- true for every answer produced
+        while tracing was off, which is most of the history predating
+        2026-08-21. Callers skip posting rather than inventing one.
+        """
+        import psycopg
+
+        with psycopg.connect(self._dsn, connect_timeout=5) as connection:
+            row = connection.execute(
+                "SELECT otel_trace_id FROM rag_retrieval_trace WHERE trace_id = %s",
+                (trace_id,),
+            ).fetchone()
+        return str(row[0]) if row and row[0] else None
+
 
 class PostgresConversationStore:
     """Durable, cross-worker replacement for `RagAgent`'s in-process