[yy-code-nv]

Automated release from i4.

_source_commit: b3866eb30721bf68dce73380563235d39fa5a622-dirty
_dest_commit (base): bf492fe2fda2108aae9b9561dc9fb9eec3fe2027

[lfengad]

Release notes: default-path behavior changes in this sync

Most of this release is new opt-in features (off by default), refactors and tests. The following changes affect existing code paths.

Behavior changes

1. Reasoner audio: with model.config.sound_und=True, video soundtracks are no longer extracted by default. Set sound_und_config.extract_audio_from_video=True to restore it. Standalone audio inputs are unaffected.
2. Multiview attention (joint_attn_implementation="multiview") now routes from the per-camera, LiDAR and action layout metadata carried by each packed sequence:
   • Packs without that metadata use dense attention.
   • Sound packs that carry layout metadata now raise an error instead of silently falling back to dense.
   • Packs from the shipped multiview datasets carry the metadata and are unaffected.
3. shift_lidar applies per sample: LiDAR-only samples in mixed batches now get the configured shift_lidar. Previously only all-LiDAR batches did. This affects recipes that set shift_lidar, such as the transfer-auto recipes.
4. RandomMixedJointDataLoader:
   • Deferred samples and the lookahead limit are now tracked per source, so the realized mix follows the configured sampling probabilities.
   • Batch composition for a given seed differs from before.
   • Batches carry a _packing_budget dict.
5. TokenMixControlConfig.log_every_n_batches removed: packing and budget statistics moved to the new monitors. Configs that set it must drop the field.

Fixes that change results in specific cases

• EveryNDrawSample: restores MoE router accumulators after sampling, so sampling no longer perturbs router updates. MoE generator runs with aux-loss-free balancing will see different training trajectories.
• AR multiview inference: now passes view ids when num_view_embeddings > 0, matching training.
• Rolling static caption limit: raised from 576 to 1024 tokens.
• easy_io: only a missing boto3, botocore or multistorageclient is tolerated. Other import errors now surface.

There are no checkpoint format changes and no removed public APIs beyond item 5.

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