PHP 8.1+ throws TypeError when using an array as array key.
Old flat-format loop iterated nested { examName: { group: [fids] } }
and tried $allowed[$arrayValue] = true, causing a fatal error and
returning ok:false ("Error al guardar") on every toma signing attempt.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>