feat: structured source document references in graph-rag responses (#1035)

specs/api/components/schemas/rag/GraphRagResponse.yaml

@@ -23,6 +23,13 @@ properties:
     description: Provenance triples for this explain event (inline, no follow-up query needed)
     items:
       $ref: '../common/Triple.yaml'
+  sources:
+    type: array
+    description: |
+      Source documents the answer was derived from, deduplicated and sorted
+      by URI. Present on the final message (end_of_session true).
+    items:
+      $ref: './Source.yaml'
   end_of_stream:
     type: boolean
     description: Indicates LLM response stream is complete

specs/api/components/schemas/rag/Source.yaml

@@ -0,0 +1,15 @@
+type: object
+description: |
+  Source document reference. Produced by tracing the graph edges used for
+  retrieval back to the documents they were extracted from.
+properties:
+  uri:
+    type: string
+    description: Source document URI
+    example: urn:document:5a90a175-9906-4dcb-b482-a8c1b6cbf9e0
+  title:
+    type: string
+    description: Document title (empty when the document has none)
+    example: Quantum Mechanics Primer
+required:
+  - uri

specs/api/paths/flow/graph-rag.yaml

@@ -118,6 +118,9 @@ post:
                   - Quantum information theory
                   - Computational complexity theory
                 end-of-stream: false
+                sources:
+                  - uri: urn:document:5a90a175-9906-4dcb-b482-a8c1b6cbf9e0
+                    title: Quantum Mechanics Primer
             streamingChunk:
               summary: Streaming response chunk
               value: