Background job runs into Cron importance classifier training failed: Call to undefined method Rubix\\ML\\Datasets\\Unlabeled::numFeatures()

Steps to reproduce

1. Run mail 4.2.0-RC2 on 30.0.5

Expected behavior

No errors

Actual behavior

{
  "reqId": "jK0bvfjrNkYDBoltJx8C",
  "level": 3,
  "time": "2025-02-02T03:00:56+00:00",
  "remoteAddr": "",
  "user": "--",
  "app": "mail",
  "method": "",
  "url": "--",
  "message": "Cron importance classifier training failed: Call to undefined method Rubix\\ML\\Datasets\\Unlabeled::numFeatures()",
  "userAgent": "--",
  "version": "30.0.5.1",
  "exception": {
    "Exception": "Error",
    "Message": "Call to undefined method Rubix\\ML\\Datasets\\Unlabeled::numFeatures()",
    "Code": 0,
    "Trace": [
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/FeatureExtraction/CompositeExtractor.php",
        "line": 53,
        "function": "extract",
        "class": "OCA\\Mail\\Service\\Classification\\FeatureExtraction\\SubjectExtractor",
        "type": "->"
      },
      {
        "function": "OCA\\Mail\\Service\\Classification\\FeatureExtraction\\{closure}",
        "class": "OCA\\Mail\\Service\\Classification\\FeatureExtraction\\CompositeExtractor",
        "type": "::",
        "args": [
          "*** sensitive parameters replaced ***"
        ]
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/functions.php",
        "line": 19,
        "function": "array_map"
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/FeatureExtraction/CompositeExtractor.php",
        "line": 52,
        "function": "OCA\\Mail\\array_flat_map"
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/ImportanceClassifier.php",
        "line": 408,
        "function": "extract",
        "class": "OCA\\Mail\\Service\\Classification\\FeatureExtraction\\CompositeExtractor",
        "type": "->"
      },
      {
        "function": "OCA\\Mail\\Service\\Classification\\{closure}",
        "class": "OCA\\Mail\\Service\\Classification\\ImportanceClassifier",
        "type": "::",
        "args": [
          "*** sensitive parameters replaced ***"
        ]
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/ImportanceClassifier.php",
        "line": 402,
        "function": "array_map"
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/ImportanceClassifier.php",
        "line": 193,
        "function": "getFeaturesAndImportance",
        "class": "OCA\\Mail\\Service\\Classification\\ImportanceClassifier",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/Service/Classification/ImportanceClassifier.php",
        "line": 234,
        "function": "buildDataSet",
        "class": "OCA\\Mail\\Service\\Classification\\ImportanceClassifier",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/apps/mail/lib/BackgroundJob/TrainImportanceClassifierJob.php",
        "line": 72,
        "function": "train",
        "class": "OCA\\Mail\\Service\\Classification\\ImportanceClassifier",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/lib/public/BackgroundJob/Job.php",
        "line": 61,
        "function": "run",
        "class": "OCA\\Mail\\BackgroundJob\\TrainImportanceClassifierJob",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/lib/public/BackgroundJob/TimedJob.php",
        "line": 88,
        "function": "start",
        "class": "OCP\\BackgroundJob\\Job",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/lib/public/BackgroundJob/TimedJob.php",
        "line": 75,
        "function": "start",
        "class": "OCP\\BackgroundJob\\TimedJob",
        "type": "->"
      },
      {
        "file": "/path/to/nextcloud/cron.php",
        "line": 162,
        "function": "execute",
        "class": "OCP\\BackgroundJob\\TimedJob",
        "type": "->"
      }
    ],
    "File": "/path/to/nextcloud/apps/mail/lib/Service/Classification/FeatureExtraction/SubjectExtractor.php",
    "Line": 89,
    "message": "Cron importance classifier training failed: Call to undefined method Rubix\\ML\\Datasets\\Unlabeled::numFeatures()",
    "exception": [],
    "CustomMessage": "Cron importance classifier training failed: Call to undefined method Rubix\\ML\\Datasets\\Unlabeled::numFeatures()"
  },
  "id": "679f2c6dc11d1"
}

Mail app version

No response

Nextcloud version

No response

Mailserver or service

No response

Operating system

No response

PHP engine version

None

Nextcloud memory caching

No response

Web server

None

Database

None

Additional info

No response

Start with apps/mail/lib/Service/Classification/FeatureExtraction/SubjectExtractor.php at line 89 and trace how CompositeExtractor.php and ImportanceClassifier.php build the training dataset. Reproduce the failure through TrainImportanceClassifierJob.php or cron.php, then verify that importance classifier training completes without the undefined Unlabeled::numFeatures() error.