Well, this is what happened, in case anybody runs in the same problem:
In the configuration file I had the following code:
'newSystemSettings' => array(
'core_path' => array( // key
'key' => 'core_path',
'name' => 'Petitions core path',
'description' => '',
'namespace' => 'petitions',
'xtype' => 'textfield',
'value' => '{base_path}_extras/petitions/core/components/petitions/',
'area' => 'general',
),
meaning that I instructed Bootstrap to add an entry to the system settings named precisely
core_path, which pretty much messed everything up.
I was under the assumption that Bootstrap would have added
petitions.core_path instead, or that somehow MODx didn't confuse components settings with core settings. But it did, and everything broke.