Move chunks into the canonical source model

internal/framework/pipeline/debug_test.go

@@ -28,3 +28,24 @@ func TestDebugSourceDocumentPreservesUnitReferences(t *testing.T) {
 		t.Fatalf("source document ref = %q after debug mutation, want source-1", got)
 	}
 }
+
+func TestDebugSourceChunkPreservesReference(t *testing.T) {
+	doc := validSourceDocument()
+	chunk := source.Chunk{
+		ID: "chunk-1", SourceID: doc.ID, Index: 0,
+		Ref:     source.SourceRef{SourceID: doc.ID, StartUnitID: 1, EndUnitID: 1},
+		Content: []byte("chunk content"), MediaType: "text/plain", Units: doc.Units[:1],
+	}
+	envelope := debugSourceChunkEnvelope(chunk)
+	encoded, err := json.Marshal(envelope)
+	if err != nil {
+		t.Fatalf("Marshal(debug source chunk) error = %v, want nil", err)
+	}
+	var decoded debugSourceChunk
+	if err := json.Unmarshal(encoded, &decoded); err != nil {
+		t.Fatalf("Unmarshal(debug source chunk) error = %v, want nil", err)
+	}
+	if decoded.Ref != chunk.Ref {
+		t.Fatalf("debug chunk ref = %#v, want %#v", decoded.Ref, chunk.Ref)
+	}
+}