[faresobeid]

Moves BatchPacker (35 lines) from orchestrator/packing.py into orchestrator/batch.py and deletes packing.py. The class only wraps build_bin_cost and prepare_batch, which already live in batch.py.

Item 6 of the orchestrator review.

Behavior change: none (pure move; the import in orchestrator.py is updated).

Checks

• pytest tests/unit/orchestrator tests/unit/test_configs* -m "not gpu": 291 passed
• ruff check, ruff format --check: clean
• python -c "import prime_rl.orchestrator.orchestrator" OK
• Equivalence: the class body is copied byte for byte (git diff shows only the move and the import lines).

GPU checks: none needed.

Conflicts

• refactor: MFU as torchtitan computes it; relative packing cost #3840 (FLOP estimator): textual, in the batch.py imports only.
• refactor: orchestrator as hook-wired components with per-component configs #3652: its Shipper imports BatchPacker from packing, which becomes a one-line change to from prime_rl.orchestrator.batch import BatchPacker.
• feat: by-handle payload segments: reader, packing, CP-window reads, GC #3819, feat: by-handle payload fields table (TRR weights, score-centering logprobs) #3836, feat: exact score centering over the sampling mask (arXiv:2609.20807) #3794 touch other parts of batch.py.

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Note

Low Risk
Pure file move and import path update with no logic changes to training batch packing.

Overview
Colocates batch packing with the bin-packing helpers it already delegates to.

BatchPacker moves from orchestrator/packing.py into orchestrator/batch.py next to build_bin_cost and prepare_batch; packing.py is removed. The orchestrator now imports BatchPacker from batch instead of packing. Class behavior and pack() semantics are unchanged.

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