CakePHP buildRules not firing on hasMany nested assocation delete - php

Question

I am having issue with build rules not firing deleting 1 element from a HasMany association on a model in CakePHP 3. My base table (Settings) is structured with the following association:
<?php
// SettingsTable.php
public function initialize(array $config)
{
parent::initialize($config);
$this->hasMany('Mappings', [
'foreignKey' => 'mappings_id',
'saveStrategy' => 'replace'
]);
}
The associated mappings table has custom rule in it's model that checks for the existence of children in the values table, prior to letting a mapping be deleted:
<?php
// MappingsTable.php
public function initialize(array $config)
{
parent::initialize($config);
$this->hasMany('Values', [
'foreignKey' => 'values_id',
'saveStrategy' => 'replace'
]);
}
public function buildRules(RulesChecker $rules): RulesChecker
{
$rules->addDelete(/* Has children rule, prevents deletion if children are found in Values table */);
}
I am using the following to update the settings table, and delete a nested mapping table entry (id 3):
<?php
$requestData = [
'title' => 'A new updated title',
'mappings' => [
['id' => 1, 'sort_order' => '5'],
['id' => 2, 'sort_order' => '10'],
// mappings id 3 was previously defined, but removed to make patchEntity() / save() delete it
]
];
$settingsTable->patchEntity($settingEntity, $requestData, [
'associated' => ['Mappings', 'Mappings.Values']
]);
$settingsTable->save($settingEntity);
Based on what I read about setting the saveStradegy key to replace for the hasMany association in the cake docs here, it seems like this should work.
The delete on the mapping with id 3 does fire in cake using this code, but for some reason the buildRules() call in the 2nd code spinet never fires. $rules->addDelete() never fires if there are child values on a mapping, and cake is forced to default to show the MySQL foreign key constraint failure message, rather than a cleaner build rule failure:
"SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (`db`.`values`, CONSTRAINT `values_fk` FOREIGN KEY (`field_id`) REFERENCES `fields` (`id`))"
What do I need to do to get the buildRules() on MappingsTable to fire when when a mapping is removed from a setting, like I am above?
Any help is appreciated!