[BUG] SFT validation fails when use_sequence_packing is enabled

[XChen-Zero]

Description

When use_sequence_packing is enabled in SFT training, validation fails during val_step.

In the current implementation:

• train_step wraps the loss function with SequencePackingSFTLossWrapper
• val_step directly uses the raw loss function

As a result, when sequence packing is enabled, forward_step receives incompatible
inputs and validation fails at runtime.

Affected Code

roll/pipeline/sft/sft_worker.py

Expected Behavior

Validation should apply the same loss wrapper as training when
use_sequence_packing is enabled, so that SFT training and validation work
correctly with sequence packing.

Additional Context

I have submitted a PR that fixes this issue by applying
SequencePackingSFTLossWrapper in val_step:

• PR: XChen-Zero:fix/sft-val-sequence-packing