Fix dataset.truncate calls to handle MySQL FK constraints

The previous fix only addressed TableTruncator, but some code paths
directly call dataset.truncate (e.g., purge_and_reseed_service_instances!
and purge_and_reseed_started_apps!), which bypasses TableTruncator
and fails with FK constraint violations on MySQL.

Solution: Added truncate_with_fk_handling helper method to both
repository classes that wraps dataset.truncate with the same
db.synchronize + SET FOREIGN_KEY_CHECKS pattern to ensure all
operations run on the same connection.

This fixes the remaining MySQL 8.2 test failure in
ServiceUsageEventRepository#purge_and_reseed_service_instances!

Author: joyvuu-dave

app/repositories/app_usage_event_repository.rb

@@ -88,7 +88,7 @@ def create_from_build(build, state)
       end
 
       def purge_and_reseed_started_apps!
-        AppUsageEvent.dataset.truncate
+        truncate_with_fk_handling(AppUsageEvent.dataset)
 
         column_map = {
           app_name: :parent_app__name,
@@ -160,6 +160,22 @@ def delete_events_older_than(cutoff_age_in_days)
       def buildpack_name_for_app(app)
         CloudController::UrlSecretObfuscator.obfuscate(app.custom_buildpack_url || app.detected_buildpack_name)
       end
+
+      def truncate_with_fk_handling(dataset)
+        db = dataset.db
+        case db.database_type
+        when :postgres
+          dataset.truncate
+        when :mysql
+          # Use db.synchronize to ensure SET FOREIGN_KEY_CHECKS and TRUNCATE
+          # run on the same connection. MySQL's FOREIGN_KEY_CHECKS is session-specific.
+          db.synchronize do |conn|
+            conn.query('SET FOREIGN_KEY_CHECKS = 0')
+            conn.query("TRUNCATE TABLE #{dataset.first_source_table}")
+            conn.query('SET FOREIGN_KEY_CHECKS = 1')
+          end
+        end
+      end
     end
   end
 end

app/repositories/service_usage_event_repository.rb

@@ -54,7 +54,7 @@ def updated_event_from_service_instance(service_instance)
       end
 
       def purge_and_reseed_service_instances!
-        ServiceUsageEvent.dataset.truncate
+        truncate_with_fk_handling(ServiceUsageEvent.dataset)
 
         column_map = {
           # using service_instance guid because we need a unique guid for the service_usage_event.  the database will not generate these for us.
@@ -94,6 +94,24 @@ def purge_and_reseed_service_instances!
       def delete_events_older_than(cutoff_age_in_days)
         Database::OldRecordCleanup.new(ServiceUsageEvent, cutoff_age_in_days: cutoff_age_in_days, keep_at_least_one_record: true, keep_running_records: true).delete
       end
+
+      private
+
+      def truncate_with_fk_handling(dataset)
+        db = dataset.db
+        case db.database_type
+        when :postgres
+          dataset.truncate
+        when :mysql
+          # Use db.synchronize to ensure SET FOREIGN_KEY_CHECKS and TRUNCATE
+          # run on the same connection. MySQL's FOREIGN_KEY_CHECKS is session-specific.
+          db.synchronize do |conn|
+            conn.query('SET FOREIGN_KEY_CHECKS = 0')
+            conn.query("TRUNCATE TABLE #{dataset.first_source_table}")
+            conn.query('SET FOREIGN_KEY_CHECKS = 1')
+          end
+        end
+      end
     end
   end
 end