Training previews, tracking and recovery

Recovery now verifies the complete run configuration, including model and dataset references, before reusing checkpoints. A corrupt saved GRPO baseline fails with recovery instructions instead of silently grading the same tasks again. Environments requiring a package build fail explicitly when no package builder is installed; prebuilt environment images remain supported.

Training admission pins dataset, model, and teacher Volumes to committed revisions. A later upload cannot silently change a run on recovery. Missing revisions fail before the run starts.

exportTo copies a managed runtime’s complete outputs into a Ready ReadWriteOnce Volume through a bounded CPU Job under the training cap. Completion identifies the revision committed by that export attempt. Export jobs follow parent suspension, cancellation, and funding stops. A failed final Volume commit now fails the node attempt instead of reporting success.