Add raw-completion debug prints for first 2 problems

Disable flashinfer sampler (no nvcc in job containers)

trackio: report_to=none + arm callback logging into single session

Fix argparse name: args.num_epochs

Fix scoring OOM (chunked logsumexp NLL), expandable_segments, gradient checkpointing

TailSFT repro: pass@k GSM8K eval script

TailSFT repro: train script (scoring + 3 SFT arms)

initial commit