API: Include custom layer names in stackup

api/proto/board/board.proto

@@ -95,6 +95,10 @@ message BoardStackupLayer
   BoardStackupDielectricLayer dielectric = 5;
   kiapi.common.types.Color color = 6;
   string material_name = 7;
+
+  // The name of the layer shown in the KiCad GUI, which may be a default value like "F.Cu" or may
+  // have been customized by the user.  This field does not apply to dielectric layers.
+  string user_name = 8;
 }
 
 message BoardStackup

pcbnew/api/api_handler_pcb.cpp

@@ -675,6 +675,18 @@ HANDLER_RESULT<BoardStackupResponse> API_HANDLER_PCB::handleGetStackup(
 
     any.UnpackTo( response.mutable_stackup() );
 
+    // User-settable layer names are not stored in BOARD_STACKUP at the moment
+    for( board::BoardStackupLayer& layer : *response.mutable_stackup()->mutable_layers() )
+    {
+        if( layer.type() == board::BoardStackupLayerType::BSLT_DIELECTRIC )
+            continue;
+
+        PCB_LAYER_ID id = FromProtoEnum<PCB_LAYER_ID>( layer.layer() );
+        wxCHECK2( id != UNDEFINED_LAYER, continue );
+
+        layer.set_user_name( frame()->GetBoard()->GetLayerName( id ) );
+    }
+
     return response;
 }