Improve logging around blueprint saving during shutdown (#5664)

### What
* Part of #5629

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crates/re_viewer/src/app.rs

@@ -974,8 +974,10 @@ impl App {
                             store_hub.set_active_recording_id(store_id.clone());
                         }
                         StoreKind::Blueprint => {
-                            re_log::debug!("Activating newly loaded blueprint");
                             if let Some(info) = entity_db.store_info() {
+                                re_log::debug!(
+                                    "Activating blueprint that was loaded from {channel_source}"
+                                );
                                 let app_id = info.application_id.clone();
                                 store_hub.set_blueprint_for_app_id(store_id.clone(), app_id);
                             } else {
@@ -1179,20 +1181,26 @@ impl eframe::App for App {
     }
 
     fn save(&mut self, storage: &mut dyn eframe::Storage) {
-        if self.startup_options.persist_state {
-            // Save the app state
-            eframe::set_value(storage, eframe::APP_KEY, &self.state);
-
-            // Save the blueprints
-            // TODO(#2579): implement web-storage for blueprints as well
-            if let Some(hub) = &mut self.store_hub {
-                match hub.gc_and_persist_app_blueprints(&self.state.app_options) {
-                    Ok(f) => f,
-                    Err(err) => {
-                        re_log::error!("Saving blueprints failed: {err}");
-                    }
-                };
-            }
+        if !self.startup_options.persist_state {
+            return;
+        }
+
+        re_tracing::profile_function!();
+
+        // Save the app state
+        eframe::set_value(storage, eframe::APP_KEY, &self.state);
+
+        // Save the blueprints
+        // TODO(#2579): implement web-storage for blueprints as well
+        if let Some(hub) = &mut self.store_hub {
+            match hub.gc_and_persist_app_blueprints(&self.state.app_options) {
+                Ok(f) => f,
+                Err(err) => {
+                    re_log::error!("Saving blueprints failed: {err}");
+                }
+            };
+        } else {
+            re_log::error!("Could not save blueprints: the store hub is not available");
         }
     }
 

crates/re_viewer/src/store_hub.rs

@@ -367,33 +367,40 @@ impl StoreHub {
         // there may be other Blueprints in the Hub.
 
         for (app_id, blueprint_id) in &self.blueprint_by_app_id {
-            if let Some(blueprint) = self.store_bundle.get_mut(blueprint_id) {
-                if self.blueprint_last_save.get(blueprint_id) != Some(&blueprint.generation()) {
-                    if app_options.blueprint_gc {
-                        blueprint.gc_everything_but_the_latest_row();
-                    }
+            let Some(blueprint) = self.store_bundle.get_mut(blueprint_id) else {
+                re_log::debug!("Failed to find blueprint {blueprint_id}.");
+                continue;
+            };
+            if self.blueprint_last_save.get(blueprint_id) == Some(&blueprint.generation()) {
+                continue; // no change since last save
+            }
 
-                    #[cfg(not(target_arch = "wasm32"))]
-                    {
-                        let blueprint_path = default_blueprint_path(app_id)?;
-                        re_log::debug_once!("Saving blueprint for {app_id} to {blueprint_path:?}");
+            if app_options.blueprint_gc {
+                blueprint.gc_everything_but_the_latest_row();
+            }
 
-                        let messages = blueprint.to_messages(None)?;
+            #[cfg(not(target_arch = "wasm32"))]
+            {
+                let blueprint_path = default_blueprint_path(app_id)?;
 
-                        // TODO(jleibs): Should we push this into a background thread? Blueprints should generally
-                        // be small & fast to save, but maybe not once we start adding big pieces of user data?
-                        crate::saving::encode_to_file(&blueprint_path, messages.iter())?;
+                let messages = blueprint.to_messages(None)?;
 
-                        self.blueprint_last_save
-                            .insert(blueprint_id.clone(), blueprint.generation());
-                    }
-                    #[cfg(target_arch = "wasm32")]
-                    {
-                        _ = app_id;
-                    }
-                }
+                // TODO(jleibs): Should we push this into a background thread? Blueprints should generally
+                // be small & fast to save, but maybe not once we start adding big pieces of user data?
+                crate::saving::encode_to_file(&blueprint_path, messages.iter())?;
+
+                re_log::debug!("Saved blueprint for {app_id} to {blueprint_path:?}");
+
+                self.blueprint_last_save
+                    .insert(blueprint_id.clone(), blueprint.generation());
+            }
+
+            #[cfg(target_arch = "wasm32")]
+            {
+                _ = app_id;
             }
         }
+
         Ok(())
     }