Balance sheet cache layer, non-blocking sync UI (#2356)

* Balance sheet cache layer with cache-busting

* Update family cache timestamps during Sync

* Less blocking sync loaders

* Consolidate family data caching key logic

* Fix turbo stream broadcasts

* Remove dev delay

* Add back account group sorting

app/controllers/accountable_sparklines_controller.rb

@@ -2,25 +2,24 @@ class AccountableSparklinesController < ApplicationController
   def show
     @accountable = Accountable.from_type(params[:accountable_type]&.classify)
 
-    # Pre-load the series to catch any errors before rendering
-    @series = Rails.cache.fetch(cache_key) do
-      account_ids = family.accounts.active.where(accountable_type: @accountable.name).pluck(:id)
+    etag_key = cache_key
 
-      builder = Balance::ChartSeriesBuilder.new(
-        account_ids: account_ids,
-        currency: family.currency,
-        period: Period.last_30_days,
-        favorable_direction: @accountable.favorable_direction,
-        interval: "1 day"
-      )
+    # Use HTTP conditional GET so the client receives 304 Not Modified when possible.
+    if stale?(etag: etag_key, last_modified: family.latest_sync_completed_at)
+      @series = Rails.cache.fetch(etag_key, expires_in: 24.hours) do
+        builder = Balance::ChartSeriesBuilder.new(
+          account_ids: account_ids,
+          currency: family.currency,
+          period: Period.last_30_days,
+          favorable_direction: @accountable.favorable_direction,
+          interval: "1 day"
+        )
 
-      builder.balance_series
+        builder.balance_series
+      end
+
+      render layout: false
     end
-
-    render layout: false
-  rescue => e
-    Rails.logger.error "Accountable sparkline error for #{@accountable&.name}: #{e.message}"
-    render partial: "accountable_sparklines/error", layout: false
   end
 
   private
@@ -28,7 +27,15 @@ class AccountableSparklinesController < ApplicationController
       Current.family
     end
 
+    def accountable
+      Accountable.from_type(params[:accountable_type]&.classify)
+    end
+
+    def account_ids
+      family.accounts.active.where(accountable_type: accountable.name).pluck(:id)
+    end
+
     def cache_key
-      family.build_cache_key("#{@accountable.name}_sparkline")
+      family.build_cache_key("#{@accountable.name}_sparkline", invalidate_on_data_updates: true)
     end
 end