Remove warning "Cannot find root container" (#8058)

* Closes #8051
* Related to #8051

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)

Author: emilk

crates/viewer/re_blueprint_tree/src/blueprint_tree.rs

@@ -187,7 +187,9 @@ impl BlueprintTree {
         let container_id = blueprint.root_container;
 
         let Some(container_blueprint) = blueprint.containers.get(&container_id) else {
-            re_log::warn_once!("Cannot find root container {container_id}");
+            // This happens after a blueprint reset (or there was no blueprint).
+            // TODO(#8056): refactor all of this
+            re_log::debug!("Cannot find root {container_id} in BlueprintTree (b/c recent reset?)");
             return;
         };
 

crates/viewer/re_viewport/src/viewport.rs

@@ -246,6 +246,7 @@ impl<'a> Viewport<'a> {
                         reset = true;
                     } else {
                         let parent_id = parent_container.unwrap_or(self.blueprint.root_container);
+                        re_log::trace!("Adding space-view {space_view_id} to parent {parent_id}");
                         let tile_id = self.tree.tiles.insert_pane(space_view_id);
                         let container_tile_id = blueprint_id_to_tile_id(&parent_id);
                         if let Some(egui_tiles::Tile::Container(container)) =
@@ -262,7 +263,7 @@ impl<'a> Viewport<'a> {
                                 );
                             }
                         } else {
-                            re_log::trace!("Root was not a container - will re-run auto-layout");
+                            re_log::trace!("Parent was not a container - will re-run auto-layout");
                             reset = true;
                         }
                     }
@@ -275,6 +276,7 @@ impl<'a> Viewport<'a> {
                         .tree
                         .tiles
                         .insert_container(egui_tiles::Container::new(container_kind, vec![]));
+                    re_log::trace!("Adding container {container_kind:?} to parent {parent_id}");
                     if let Some(egui_tiles::Tile::Container(container)) =
                         self.tree.tiles.get_mut(blueprint_id_to_tile_id(&parent_id))
                     {

crates/viewer/re_viewport_blueprint/src/viewport_blueprint.rs

@@ -92,6 +92,9 @@ impl ViewportBlueprint {
             past_viewer_recommendations: results.component_batch(),
         };
 
+        let root_container: Option<ContainerId> = root_container.map(|id| id.0.into());
+        re_log::trace_once!("Loaded root_container: {root_container:?}");
+
         let all_space_view_ids: Vec<SpaceViewId> = blueprint_db
             .tree()
             .children
@@ -143,19 +146,19 @@ impl ViewportBlueprint {
         let tree = build_tree_from_space_views_and_containers(
             space_views.values(),
             containers.values(),
-            root_container.clone(),
+            root_container,
         );
 
+        re_log::trace_once!("Loaded tree: {tree:#?}");
+
         let past_viewer_recommendations = past_viewer_recommendations
             .unwrap_or_default()
             .iter()
             .cloned()
             .collect();
 
-        let root_container_or_placeholder = root_container.clone().map_or_else(
-            || ContainerId::hashed_from_str("placeholder_root_container"),
-            |id| id.0.into(),
-        );
+        let root_container_or_placeholder = root_container
+            .unwrap_or_else(|| ContainerId::hashed_from_str("placeholder_root_container"));
 
         Self {
             space_views,
@@ -909,7 +912,7 @@ impl ViewportBlueprint {
 fn build_tree_from_space_views_and_containers<'a>(
     space_views: impl Iterator<Item = &'a SpaceViewBlueprint>,
     containers: impl Iterator<Item = &'a ContainerBlueprint>,
-    root_container: Option<RootContainer>,
+    root_container: Option<ContainerId>,
 ) -> egui_tiles::Tree<SpaceViewId> {
     re_tracing::profile_function!();
     let mut tree = egui_tiles::Tree::empty("viewport_tree");
@@ -933,7 +936,6 @@ fn build_tree_from_space_views_and_containers<'a>(
     // And finally, set the root
 
     if let Some(root_container) = root_container {
-        let root_container = ContainerId::from(root_container.0);
         tree.root = Some(blueprint_id_to_tile_id(&root_container));
     }